Technical Sessions

Monday, September 21, 2020

11:00 am | Inter-Calibration and Validation of Operational Sensors

Performance comparison between sensors of differing scientific objectives, capabilities, and mission parameters to assess measurement bias and uncertainty.

  • Post-launch calibration using onboard and/or vicarious techniques
  • Retrievals through data assimilation with various data used for validation
  • Results of particular approaches, validation campaigns, and experiments
  • Techniques, platforms, and instruments for validation
  • Application of calibration results to scientific measurements
  • Requirements and potential approaches for the calibration of global satellite observing sensors

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New Perspectives for Inter-Calibration using Sentinel-3 Tandem Data
Sebastien Clerc, Nicolas Lamquin, Ludovic Bourg – ACRI-ST; Dave Smith – RAL Space; Sam Hunt – The National Physical Laboratory (NPL); Jonathan Mittaz – University of Reading; Craig Donlon – The European Space Agency (ESA)

ABSTRACT: During the commissioning phase of Sentinel-3B, the satellite was placed in close formation with Sentinel-3A for several months. This configuration provides a unique opportunity to compare measurements from the two satellites, opening new perspectives for inter-calibration. We will briefly present an overview of activities performed using tandem data and describe in more details two applications for Sentinel-3 optical instruments.

A first application is the estimation of inter-satellite calibration biases. We describe the methodology used to intercompare the multispectral OLCI A and B instruments, using re-gridding, conversion to reflectance and spectral adjustment of the Rayleigh signal. Statistics are then computed for the different classes of scene. Clouds are particularly interesting targets because of their abundance and white reflectance spectrum. Thanks to this method, it has been possible to estimated inter-calibration biases with an uncertainty lower than 0.5% across the full instrument field-of-view. Biases have been shown to be temporally stable during the tandem period.

The efficiency of this inter-calibration has been assessed by aligning OLCI-A on OLCI-B with a custom reprocessing. We also demonstrate the positive impact on inter-comparison of Level 2 land and ocean products.

A second type of application concerns the validation of per-pixel uncertainties. For this goal, differences between SLSTR A and B measurements (L1 or L2) are compared to ex-ante uncertainties provided by models. More precisely, the independent components of the uncertainties are used to normalize the inter-satellite differences. This normalized difference is expected to behave like a normal distribution with a standard deviation of 1. Although the agreement is relatively satisfactory for data with the highest quality level, some significant variations have been observed for lower quality indices. This information can help improve processing algorithms and/or uncertainty estimates.

Radiometric Comparison of OCO-2, OCO-3 and Aqua MODIS
Shanshan Yu, Robert Rosenberg, Carol Bruegge, Lars Chapsky, Dejian Fu, Graziela Rodrigues, David Crisp, Annmarie Eldering – Jet Propulsion Laboratory, California Institute of Technology; Tommy Taylor, Heather Cronk – Colorado State University, Amit Angal – Science Systems and Applications, Inc. (SSAI); Jack Xiong – NASA Goddard Space Flight Center

ABSTRACT: The Orbiting Carbon Observatory 2 (OCO-2) and the Orbiting Carbon Observatory 3 (OCO-3) are NASA Earth Science missions designed to measure carbon dioxide in Earth’s atmosphere. OCO-2 was inserted at the front of the 705 km Afternoon Constellation (A-Train) in August 2014, and flies about 7 minutes ahead of the Aqua spacecraft. OCO-3 was mounted on the Japanese Experiment Module Exposed Facility onboard the International Space Station (ISS) in May 2019. OCO-2 and OCO-3 use three-channel grating spectrometers to measure reflected sunlight within the O2 band at 0.76 micron and two CO2 bands at 1.61 micron and 2.06 micron. The grating of each channel disperses light onto 1016 spectral channels of a focal plane array, yielding spectra with a resolution of ~ 0.04, 0.08, and 0.1 nm, respectively. OCO-2 uses onboard lamps, solar observations, and lunar measurements as well as surface targets for radiometric calibration/validation. OCO-3 is equipped with onboard lamps, and can also observe the Moon a few times each year, but cannot observe the Sun due to its configuration onboard ISS.

The OCO missions require a 5% accuracy on absolute radiometric calibration to meet their CO2 accuracy requirements. Here, we describe results from the radiometric comparisons of OCO-2 and Aqua MODIS using OCO-2 nadir observations over eight desert sites and nearly simultaneous MODIS observations with sensor viewing zenith angles of 15±0.5 degree. The MODIS data are collocated into the OCO-2 geolocation grid using a 1 km circular region around each OCO-2 footprint. Without correcting for viewing geometry differences and mismatched spectral response functions, the mean and standard OCO-2/MODIS radiance ratio over the eight sites are determined to be 1.103±0.010, 1.120±0.007, 1.233±0.016 for the OCO-2 three bands, respectively. Here, we report the OCO-2 absolute radiometric calibration obtained from ongoing efforts to develop bi-directional reflectance distribution function (BRDF) models to account for the viewing geometry differences and to reduce the seasonal variations, and by correcting biases due to mismatched spectral response functions. We will also discuss the absolute radiometric comparison of OCO-2 and OCO-3 using simultaneous nadir overpasses of these desert sites.

Valuation of Calibration for Satellite Constellations
Afreen Siddiqi, Olivier de Weck – Massachusetts Institute of Technology (MIT); Brandon Russell, Will Arnold, Jeff Holt, Chris Durell – Labsphere Inc.

ABSTRACT: Earth observation systems, consisting of in-space and air borne platforms and sensors, are providing a growing number of high
resolution spatial and temporal services including agricultural crop yield predictions, local weather forecasts, and traffic management. As the
complexity of these systems increases with multi-platform elements and sophisticated processing and modeling, there are also increasing
avenues for introduction of errors. It is important to characterize and quantify the uncertainties and errors. Here, it shown that a value-chain
approach can be used for conceptualizing errors and modeling uncertainties relevant for final decisions. This approach can then be applied
for improving system value assessments and obtaining an ‘error-adjusted’ value of the remote sensing system. The error-adjusted value can
be used in optimization or trade-studies for system design. This value system is then applied, as an example, to the FLARE real world
calibration/validation system to look at potential Return on Investment (ROI) of better calibration to satellite image prices and market

Deep Convective Clouds for Sentinel-3 OLCI Cross-Calibration Monitoring
Nicolas Lamquin, Sebastien Clerc, Ludovic Bourg – ACRI-ST; Craig Donlon – The European Space Agency (ESA)/ The European Space Research and Technology Centre (ESTEC)

ABSTRACT: Few weeks after its launch in April 2018, Sentinel-3B of the European Space Agency has been put in a tandem phase with its twin Sentinel-3A already in orbit. Both platforms were on the same track with the same geometrical conditions to gather acquisitions over the same targets only thirty seconds apart. This tandem phase lasted from early June to mid October 2018 to provide a unique opportunity for each S-3 sensors to increase knowledge of payload differences, reduce uncertainties when comparing data and to homogenise differences by defining appropriate adjustments. The inter-unit consistency is critical for the mission.

The outcome of the tandem phase analysis provides a strong reference for assessing other cross-calibration methodologies, one of those being based on the use of Deep Convective Clouds (DCCs). Whereas a physical model of DCC reflectance must be provided to compare Ocean and Land Colour Instrument (OLCI) measurements with an absolute reference, DCC observations are rather used for their whiteness, brightness, and large spatial extent, for interband monitoring. In this presentation, we present and validate a DCC-based radiometric validation methodology adapted to OLCI with a specific emphasis on its ability to accurately monitor the cross-calibration of the independent sensors. We base the analysis on a careful analysis of the OLCI DCC reflectance measurements with a sensitivity assessment of the data selection employed (use of SLSTR synergetic brightness temperature or reflectance in absorption bands, analysis and handling of saturated pixels) as well as a cautious analysis of the FOV-dependency of the results.

Performance is assessed by comparisons with the cross-calibration reference of the tandem analysis, in and out of the tandem phase acquisition period. The methodology covers the complete OLCI spectrum (to the exception of absorption bands) with precision less than about 1%.

1:15 pm | Remote Sensing and Calibration of Astronomical Data

Assessing the precision and accuracy of radiometric measurements of astrophysical sources.

  • Inter-comparison of ground-test and in-orbit data
  • Methods and techniques for identifying and controlling measurement bias (systematic uncertainties)
  • Reliability of astrophysical standards
  • Inter-calibration of astronomical observing platforms
  • Establishing reliable secondary / transfer standards
  • Sensor calibration and characterization for astronomy

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The Relative Calibration System for WFIRST LED Lessons
Ray Wright, Gregory Wirth – Ball Aerospace; Phil Scott – USU/Space Dynamics Laboratory; Maxime Rizzo – Conceptual Analytics

ABSTRACT: NASA’s Wide-Field Infrared Survey Telescope (WFIRST) is a space-based observatory currently under design and initial stages of fabrication, targeted to launch in the mid-2020s. The U.S. National Academy of Science’s Astro2010 decadal survey identified WFIRST as the highest-priority mission to investigate three fundamental problems in astronomy: the dark energy content of the Universe, the evolution of the high-redshift galaxy and quasar population, and the demographics of exoplanets in our own galaxy. Ball Aerospace is currently developing the mechanical/optical assembly for WFIRST’s key imager, the Wide Field Instrument. With its leading-edge mosaic of IR detectors, this imager will provide a field of view over 100 times greater than the competing instruments on the Hubble Space Telescope, thus opening an exciting new era in sky surveys from space. To achieve the mission’s ambitious science objectives, WFI must observe celestial objects over an exceptional range of brightness with extraordinary photometric precision. Ball Aerospace and Utah State University’s Space Dynamics Laboratory (SDL) are collaborating to design and build an onboard light source system capable of helping WFI meet these stringent photometric performance requirements. This Relative Calibration System (RCS) generates light matched to the wavelengths of each of the imager’s six filters, illuminating the WFI Focal Plane Assembly (FPA) with temporally stable illumination at six logarithmically-spaced signal levels. Measuring these light levels will define a detector response ratio we’ll use to define a transfer standard relating faint objects to bright ones. This talk will highlight the engineering methods we’ve employed to select the sources for use in the calibration system, some unexpected consequences of these choices, the lessons learned from the trade studies, and what challenges lie ahead in completing the RCS.

The All-sky Visible and Infrared Astronomical Catalog Encompass 3.0: Motivation, Creation, and Validation
Jennifer Simmerer, Thomas Murdock, Leah Roach, Ryan Hartzell – Frontier Technology Inc.; Brian Muccioli – BAE Systems

ABSTRACT: Celestial objects captured in a sensor field-of-view can be used for in-situ sensor calibration and for navigation. One of the limitations on this approach is that the prediction of what objects will be visible to sensors can be highly inaccurate when sensor spectral bands do not match published stellar survey spectral bands. FTI presents Encompass v3.0, a compiled catalog of all known stars, galaxies, globular star clusters, and nebulae detectable in the visible, near-infrared, and mid-infrared portions of the electromagnetic spectrum across the entire sky. Proprietary physics-based modeling techniques enable Encompass users to create radiometrically and astrometrically relatively accurate astronomical inventories to suit a wide range of detector technologies. Derived from the Hubble Space Telescope’s Guide Star Catalog version 2.3 and the AllWISE extension of the space-based Wide-field Infrared Survey Explorer, the star catalog contains nearly 1 billion astronomical objects detectable with visible-wavelength sensors (complete to 20 mag at 0.6 um) and nearly 750 million astronomical objects detectable with infrared-wavelength sensors (complete to 17 mag at 3 um) over the whole sky. Object positions are accurate to 2 urad (0.4 arcsec) at all brightness ranges and the catalog supports physics-based spectral modeling for any mission passband between 0.4 and 20 um. Catalogs in derived custom passbands were validated against published astronomical surveys APASS, GLIMPSE, and DIRBE and found to be accurate to better than 0.5 mag--sufficient to determine whether sources will be visible for mission planning purposes. Encompass supports derived program catalogs filtered by brightness and position as well as calibration and reference catalogs filtered to custom source densities. We discuss the challenges of working with a large data set, outline the validation process, and present validation results.

2:15 pm | Calibration Methods Using Celestial Objects

Presentation of radiometric measurements and calibration methods using the Sun, Moon, stars, and other celestial objects in the ultra-violet, visible, and infrared wavelengths

  • Characterization and calibration of celestial sources for on-orbit sensor calibration
  • Post-launch calibration and long-term trending using celestial observations
  • Calibration accuracy using celestial objects
  • Real-life experience and lessons learned using celestial objects for radiometric sensor calibration

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The SLIM Lunar Irradiance Model, a Single Fit to 9 Instruments - Many Observations, One Moon
Hugh Kieffer – Celestial Reasonings

ABSTRACT: Lunar calibration has the potential to put all participating instruments on the same long-term stable radiometric scale. Realizing this involves significant effort on the part of instrument teams and calibration community. Among the challenges are: improving the lunar spectral-irradiance model, extracting the measured irradiance from an instrument observation, and understanding any response differences between a normal nadir observation and a lunar view. This work addresses the first of these; this year’s CALCON workshop will help address the other two.

A problem with the ROLO lunar calibration model is ’jumps’ between its underlying 32 bands, especially at longer wavelengths. This issue is also contained in the initial version of the SLIM (Spacecraft and earth- base Lunar Irradiance Model); a band-by-band methodology. By normalizing instrument measurements to a high-spectral-resolution lunar reflectance spectrum, a model has now been developed that is continuous in wavelength as well as geometry.

The SLIM system allows scaling each instrument band by a constant gain factor, which is found by iterative modeling. SLIM models can be polynomial to a modest power in each of the five geometric angles; phase angle, selenographic solar longitude and latitude, selenographic viewer longitude and latitude; and each of these terms can be independently be multiplied by a polynomial up to cubic in ’wave’; wavelength λ in µm, 1/λ or ln λ. A variety of numerical tools have been developed to aid in choosing which combination from this large zoo of terms works well in minimizing both residuals and the number of coefficients.

Currently, data from ROLO, Landsat-8 OLI, Hyperion, MODIS-Aqua, MODIS-Terra, SNPP-VIIRS, SeaW-IFS, PLEIADES-A, PLEIADES-B go into the model, about 87,000 points. If the instrument team supplies trends that they feel should be applied to the measurements, that is done at data ingest. Data are automatically processed for wild-points. Overall weights can be assigned to each instrument, and relative weights to each band.

After a model fit, all instruments are calibrated with that model, the empirical gain factors for each band and instrument are revised, trends can be assessed (five possible models) and applied; weights can also be revised. Residual seasonal oscillations can be quantified and applied. Then the fit process is iterated until convergence.

The calibration spectrum of all instruments mentioned plus five GOES instruments and NIST telescope observations, will be presented, revealing their relative scales. All spacecraft teams with lunar observations are invited to participate.

The East-West Response Versus Scan-angle Performance of GOES-16/17 ABI Solar Reflective Bands
Fangfang Yu – Xi Shao, Haifeng Qian – University of Maryland; Xiangqian Wu – NOAA/NESDIS/STAR

ABSTRACT: The scan mirror reflectivity of the Advanced Baseline Imager (ABI) solar reflective bands was characterized before launch to ensure calibration uniformity. To verify, a series of lunar images were collected during the GOES-16/17 ABI post-launch test/post-launch product test (PLT/PLPT) periods while the Moon transited the space within the ABI field of regard (FOR). The irradiance of each lunar image was measured by ABI and simulated by the Global Space-based Inter-Calibration System (GSICS) Implementation of the ROLO (GIRO) model. The ratio of these irradiances was used to evaluate the ABI Response versus Scan-angle (RVS) performance along the EW direction. It was found that lunar irradiance measured by ABI is very sensitive to straylight. In this study, the straylight correction algorithms were developed to remove its impacts on the illuminated lunar pixels at the shorter wavelength images. After the straylight corrections, the RVS variation along the EW direction is well within 1% for all the GOES-16/17 ABI solar reflective bands within the FOR.

Airborne LUnar Spectral Irradiance (air-LUSI) Mission – Capability Demonstration
Kevin Turpie – University of Maryland, Baltimore County; Steven Brown, John Woodward, Steve Grantham, Stephen Maxwell, Thomas Larason – National Institute of Standards and Technology (NIST); Tom Stone – U.S. Geological Survey; Andrew Gadsden, Andrew Newton – University of Guelph

ABSTRACT: The Moon is a very useful calibration target for Earth-observing sensors in orbit because its surface is radiometrically stable and it has a radiant flux comparable to Earth scenes. To predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. However, instrument calibration teams have expressed the need for an absolute lunar reference with higher accuracy.

The objective of the airborne LUnar Spectral Irradiance (air-LUSI) mission is to make highly accurate, SI-traceable measurements of lunar spectral irradiance in the VNIR spectral region from NASA’s high-altitude ER-2 aircraft. To that end, the air-LUSI system employs an autonomous, robotic telescope system that tracks the Moon in flight, and a stable spectrometer housed in an enclosure providing a robustly controlled environment. These instrument subsystems are situated in a wing pod of the ER-2 aircraft with a small dorsal view port. Through this port, the telescope can observe the Moon from above 95% of the Earth’s atmosphere.

air-LUSI successfully conducted a Demonstration Flight Campaign on five consecutive nights from 12 to 17 November 2019. Each night, the air-LUSI system observed the Moon at about 68,000 feet altitude. Each observation period lasted 30 to 40 minutes and measured the lunar spectral irradiance at wavelengths from about 380 to 1000 nm. The five flights corresponded to lunar phase angles of 10°, 21°, 34°, 46° and 59°. The measurement uncertainty is currently estimated to be about 0.8% or less through the mid-visible range. With this new capability, the air-LUSI team plans to acquire additional lunar spectral irradiance measurements and apply this state-of-the-art data set to improve the accuracy of ROLO predictions. This paper will summarize the air-LUSI objectives and provide an overview of the Demonstration Flight Campaign and lessons learned that could further improve air-LUSI accuracy in future flights.

ARCSTONE: Calibration of Lunar Spectral Reflectance from Space
Cindy Young, Constantine Lukashin, Trevor Jackson, Jacob Benheim, Michael Cooney, Warren Davis, Thuan Nguyen, Noah Ryan, David Taylor – NASA Langley Research Center; Tom Stone – U.S. Geological Survey; Greg Kopp, Alan Hoskins, Paul Smith – Laboratory for Atmospheric and Space Physics (LASP), University of Colorado; Rand Swanson, Hans Courrier, Michael Kehoe, Michael Stebbins – Resonon; Elise Minda, Christine Buleri, Alex Halterman, Tim Christianson – Quartus Engineering

ABSTRACT: Detecting and improving the scientific understanding of global trends in complex Earth systems, such as climate, increasingly depends on assimilating datasets from multiple instruments and platforms over decadal timescales. Calibration accuracy, stability, and inter-consistency among different instruments are key to developing reliable composite data records from sensors in low Earth and geostationary orbits, but achieving sufficiently low uncertainties for these performance metrics poses a significant challenge. Space-borne instruments commonly carry on-board references for calibration at various wavelengths, but these increase mass and mission complexity, and are subject to degradation in the space environment.

The Moon can be considered a natural solar diffuser which can be observed as a calibration target by most spaceborne Earth-observing instruments. Since the lunar surface reflectance is effectively time-invariant, establishing the Moon as a high-accuracy calibration reference enables broad inter-calibration opportunities even between temporally non-overlapping instruments and provides an exo-atmospheric absolute radiometric standard. The ARCSTONE mission goal is to establish the Moon as a reliable reference for high-accuracy on-orbit calibration in the visible and near-infrared spectral region. The ARCSTONE instrument is a compact spectrometer, which will be packaged on a CubeSat intended for low Earth orbit. It will measure the lunar spectral reflectance with accuracy < 0.5% (k=1), sufficient to establish an SI-traceable absolute lunar calibration standard when referenced to the spectral solar irradiance across the 350 to 2300 nm spectral range. This lunar reference will help to enable high-accuracy absolute calibration and inter-calibration of past, current, and future Earth-observing sensors, meteorological imagers, and long-term climate monitoring satellite systems.

The ARCSTONE team will present the laboratory characterization results from two prototyped instruments, one operating in the UV-VNIR and the other in the SWIR. The development status of a next-generation full-spectral-range instrument, the intended approach to calibration and characterization, and the planned path toward mission implementation will also be discussed.

Tuesday, September 22, 2020

8:00 am | Radiometric Sensor Calibration Uncertainty and Error Analysis

Sensor calibration and characterization relies on models, measurements, and analysis to provide the needed data to derive results while estimating errors and uncertainties show how well the results are understood.

  • Modeled vs. measured results
  • Uncertainty and error assessment techniques
  • Measurement equipment characterization methods; both development and operational equipment
  • End-to-end system level uncertainty assessment

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Improvements to Stray Light Modeling on the Ozone Mapping and Profiler Suite
Tevis Nichols, Rebecca Schindhelm, Tyler McCracken – Ball Aerospace

ABSTRACT: The Ozone Mapping and Profiling Suite (OMPS) provides a critical capability for the measurement of atmospheric ozone levels. Two OMPS instruments are currently in orbit with a third preparing for launch on JPSS-2 (J2) and a fourth in development. OMPS is a set of three spectrometers each with different wavelength ranges covering 250nm to 1000nm. As part of the calibration and assessment of OMPS sensor, stray light levels in each spectrometer must be accurately modeled and assessed. To do this, a multi-element stray light model has been developed to accurately predict levels of stray light in each spectrometer. This model includes scatter from telescope reflecting surfaces, dispersion, and ghosts from gratings and focal plane array (FPA) windows. For J2 OMPS this model was improved with a new model for reflective surface scatter in the Limb sensor and an automated tuning method for the dispersion model to better match measured data. The model was calibrated and assessed during the ground testing campaign using a variety of light sources with various spectral and spatial characteristics. The new model improves accuracy, is faster to calibrate, is applicable across a wider variety of input scenes, and reduces the alteration of measured PSFs in the dispersion model. This presentation will cover these model improvements and their implementation in the J2 OMPS instrument calibration.

Microwave Radiometer Instability due to Infrequent Calibration
Kevin Coakley, Jolene Splett, David Walker – National Institute of Standards and Technology (NIST); Mustafa Aksoy University at Albany, State University of New York; Paul Racette – NASA

ABSTRACT: We directly quantify the effect of infrequent calibration on the stability of microwave radiometer temperature measurements (where a power measurement for the unknown source is acquired at a fixed time but calibration data are acquired at variable earlier times) with robust and non-robust implementations of a new metric. Based on our new metric, we also determine a component of uncertainty in a single measurement due to infrequent calibration effects. We apply our metric to experimental ground-based calibration data acquired from a NASA millimeter-wave imaging radiometer (MIR) and a NIST radiometer (NFRad). We demonstrate that the physical interpretation of our new metric is more clear than that of the existing variogram metric. Based on a stochastic model for NFRad, we determine the random uncertainty of our stability metric by a Monte Carlo method.

10:45 am | National Standards Technology Advancement

Opportunities for communication and collaboration between National standards laboratories and the calibration community to improve calibration technologies and methodologies.

  • Calibration traceability to standards—NIST and international
  • Relationship between primary, secondary, and transfer standards and applications to remote sensing
  • Maintenance of a valid calibration throughout instrument life
  • Activities within the community aimed at increasing the quality of our satellite-based measurements

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Detector Responsivity by Fibre Coupled Cryogenic Primary Standard at 0.1%
Malcolm White – National Institute of Standards and Technology (NIST)

ABSTRACT: We have previously presented work describing a new optical fibre-coupled cryogenic primary standard facility at NIST. The new radiometer replaced a liquid helium system as the primary standard for the traceable dissemination of the power responsivity of fibre-coupled visible and near-infrared detectors [1]. The facility has been upgraded and now uses polarisation maintaining (PM) fibre throughout, from the Fabry-Pérot fibre-coupled laser diode sources, through the variable optical attenuators with integral shutters and PM fibre beam-splitters [2]. The system is used at wavelengths of 850 nm, 1310 nm and 1550 nm, with an expanded uncertainty of 0.1 %.

This presentation will illustrate how we assessed the main contributors to the uncertainty budget and thus were able to improve the overall uncertainty from 0.4 % to 0.1 %.

We have measured the temperature dependent change of the Fresnel reflection loss and Rayleigh backscatter of PM single-mode fibre as it was cooled to 5 K. This change in Fresnel reflection accounts for a small 0.03 % correction to the room temperature beam-splitter ratio measurement between the radiometer and the device under test (DUT). We used an in-situ beam-splitter measurement technique to measure the Fresnel reflection and we confirmed the results at 1550 nm with an optical frequency domain reflectometer measurement.

Passive optical components such as fibre beam-splitters and couplers exhibit polarisation dependent loss (PDL), whereby the output signal of the device varies as a function of the input polarisation state. In our setup this affects the room temperature beam-splitter ratio between radiometer and DUT. The temperature dependence of the PDL was evaluated, using the Mueller matrix method, for fused biconical and planar polarisation maintaining fibre beam-splitters at 1310 nm and 1550 nm over the range 10 ºC to 40 ºC. The uncertainty in determining this ratio will be discussed during the presentation.

We have also assessed the impact that the temporal and spectral modal stability of the Fabry-Pérot laser diode sources have on the power responsivity of the DUT. The wavelength uncertainty that arises is incorporated into the uncertainty budget.
This work improves and further assures the performance of our optical fibre-coupled cryogenic radiometer facility.

1. M.G. White, Z.E. Ruiz, C.S. Yung, I. Vayshenker, N.A. Tomlin, M.S. Stephens, and J.H. Lehman, “Cryogenic primary standard for optical fibre power measurement”, Metrologia 55(5), 706-715 2018
2. M.G. White, E. Baumann, I. Vayshenker, Z.E. Ruiz, M.S. Stephens, M. Smid and J.H. Lehman, “The nature of fibre coupled detector responsivity measurements at 0.1 % using a primary standard”, Submitted Opt. Express, Feb. 2020

Broadband, Absolutely Calibrated Microbolometer Array Development
Michelle Stephens, Chris Yung, Nathan Tomlin, John Lehman – National Institute of Standards and Technology (NIST);
David Harber, Karl Heuerman, Joel Rutkowski, Cameron Straatsma, Odele Coddington – Laboratory for Atmospheric and Space Physics (LASP), University of Colorado

ABSTRACT: Microfabricated electrical substitution bolometers with vertically aligned carbon nanotube (VACNT) absorbers are being integrated into laboratory standards for optical laser power1 and CubeSats for solar irradiance mesurements2,3. We are building on these successes to extend the single bolometer technology to broadband microbolometer arrays with electrical substitution and VACNT absorbers. A linear array of radiometer elements has been fabricated. Each element is an uncooled bolometer with vanadium oxide (VOx) temperature measurement. Unlike existing VOx microbolometer technology where the thermistor film is incorporated into a narrow band cavity and doubles as the absorber, in these microbolometer arrays we use VACNT absorbers. Additionally, each element can be electrically heated to provide an absolute radiometric calibration through electrical substitution.

The array provides two benefits for Earth Science applications that require spectral data across many wavelengths. The first is the electrical substitution calibration on every pixel. Existing instruments are typically calibrated on the ground but then subjected to severe launch and space environments. On-orbit calibration is achieved with a reference such as a blackbody, lamp, or reference material and by ground verification. On-orbit references increase mass and power and may be degraded by the space environment. This technology eliminates the need for on-orbit references by incorporating electrical substitution calibration. By comparing the temperature rise of the bolometer when illuminated to the temperature rise when a known current is injected into a heater of known resistance, a calibrated irradiance is measured.

The second benefit is an extended spectral range. A typical microbolometer response is from 8 um to 15 um, but a VACNT absorber can extend the response to a wider 0.3 um to 100 um range. A broader spectral response in a single array can serve to reduce the number of detectors needed to span a broad wavelength range. The response above 20 µm improves measurement capabilities for applications such as Earth Radiation Budget. The combination of broadband spectral response and integrated calibration capability makes this single technology applicable to a broad range of scientific measurements.

This talk will describe the design, fabrication, and performance of the microbolometers. To date we have achieved a noise floor of ~100 K/sqrt(Hz) at 0.1 Hz. We show the expected performance of one of these arrays incorporated with a small telescope is appropriate for use on a smallsat.

Acknowledgements: This work is funded by the NASA Earth Science Technology Office.

1. M.G. White, et al., “Cryogenic primary standard for optical fibre power measurement”, Metrologia 55(5), 706-715 2018.
2. Erik Richard et al., “The compact spectral irradiance monitor flight demonstration mission”, Proc. SPIE 11131, CubeSats and SmallSats for Remote Sensing III, 1113105 (30 August 2019).
3. David Harber et al., “Compact total irradiance monitor flight demonstration”, Proc. SPIE 11131, CubeSats and SmallSats for Remote Sensing III, 111310D (30 August 2019).

Development of 300 mW Background-Compensated Planar Absolute Radiometer Operating at Room Temperature
Anna Vaskuri, Michelle Stephens, Nathan Tomlin, Christopher Yung, Andrew Walowitz, John H. Lehman – National Institute of Standards and Technology (NIST), Boulder; Cameron Straatsma, David Harber – Laboratory for Atmospheric and Space Physics (LASP), University of Colorado

ABSTRACT: NIST’s C-series isoperibol calorimeters [1] operating at room temperature have been used as reference instruments in the laser power calibrations at NIST for over 50 years. These calorimeters operate from 100 μW to 300 mW with an expanded uncertainty of 0.86% (k = 2). Recently developed vertically aligned carbon-nanotube (VACNT) absorbers, with spectrally flat and hemispherical absorptance better than 99.95%, have enabled development of planar absolute bolometers with smaller size and significantly faster measurements compared to traditional laser calorimeters.

In this work, we present the latest progress of the Planar Absolute Radiometer for Room Temperature (PARRoT) [2] currently under construction that will replace the old reference C-series calorimeters. PARRoT is based on the electrical power substitution method and it can measure laser powers up to 300 mW with a predicted expanded uncertainty better than 0.1% (k = 2). The radiometer is operated at room temperature and placed in a 15 cm cube vacuum chamber to minimize convection while still providing a compact and sturdy standard. The laser beam is transmitted to the absorber by an uncoated fused silica window with a 0.5° wedge assuring polarization independent laser power detection. PARRoT is background compensated by differential operation where the reference detector chip is driven by a constant DC power and the measuring detector chip is feedback controlled to follow the temperature of the reference detector chip. The closed loop operation makes the radiometer’s response linear across the operational power range. We have optimized the detector chip design by thermal modeling [2]. The modeled electro-optical inequivalence for a centered laser beam is 0.007% and the spatial non-uniformity is ±0.02% within 4 mm radius from the absorber’s center, meaning that PARRoT is not sensitive to small alignment offsets.

PARRoT’s differential background compensation makes it insensitive to variations in background radiation. That combined with a compact design would allow it to be used as a radiance detector standard for field calibrations and atmospheric measurements outdoors or as a transfer standard between laboratories. Similar bolometers will be launched in a CubeSat satellite next year to measure total solar irradiance [3]. By changing a few resistance values in the electronics, by changing the detector chip’s heater resistance, and modifying the thermal conductance of the heat link design, the power range of PARRoT can be modified for different applications without compromising the accuracy. For example, reducing the heater resistance and increasing the heat link’s thermal conductance can extend the power range to 2 W. This enables, for instance, direct calibration of the 1 W laser beam power in LIGO (Laser Interferometer Gravitational-wave Observatory) with an expanded uncertainty of 0.1% (k = 2) which would be an order of magnitude improvement to its current calibration against NIST’s reference calorimeter via an integrating sphere transfer standard.
Acknowledgements: Jenny and Antti Wihuri Foundation, Finland is acknowledged for the financial support of this research.
1. E. D. West et al., “A Reference Calorimeter for Laser Energy Measurements,” J. Res. Natl. Bur. Stand. (U. S.) 76A, 13–26 (1972).
2. A. Vaskuri et al., “Microfabricated bolometer based on a vertically aligned carbon nanotube absorber,” Proc. SPIE 11269, 1–12, Synthesis and Photonics of Nanoscale Materials XVII, 112690L (March 2020).
3. D. Harber et al., “Compact total irradiance monitor flight demonstration,” Proc. SPIE 11131, 1–8, CubeSats and SmallSats for Remote Sensing III, 111310D (August 2019). 

Alternative Calibration Methods of Radiometric Detectors
Jarle Gran, Trinh Tran, Marit Ulset Nordsveen – Justervesenet; Eivind Bardalen, Per Øhlckers – University of South-East Norway; Ørnulf Nordseth – Institute for Energy Technology; Ozhan Koybasi – SINTEF

ABSTRACT: The usual way of calibrating detectors or devices is to treat them as black boxes. We measure the response when the device is excited with a well-known signal. With this approach we throw away a lot of information that can be used to develop new calibration techniques. In the common European project chipS∙CALe (running from June 2019 – May 2022) we aim to develop self-induced silicon photodiodes capable of calibrating themselves in possibly remote operation. The trick is to exploit the intrinsic quantum properties of photodiodes that each photon generates exactly one electron hole pair. This is a valid assumption to about 99.9% of common calibration standard photodiodes used in laboratories today when correcting for reflectance.

Two fundamentally different approaches are explored in the chipS∙CALe project. We are developing new simple structure photodiodes with improved quantum efficiency beyond the usual 99.9 % photon to electron conversion efficiency. Because the photodiodes have a simplified structure, their losses can be simulated with 3D simulation models. With simple I-V measurements at one wavelength only, a 3D model fit can be applied, and the responsivity from 400 nm to 850 nm can be predicted.

The second method is based on exploiting the photodiode as an electrical substitution radiometer in addition to its usual quantum mode. The incoming radiation is converted either to a photocurrent, as in a traditional photodiode, or to heat, using electrical substitution to determine the power of the absorbed radiation. The true internal quantum deficiency is measured by this method as it is the same absorber used in both application modes and heat is generated by forward bias of the photodiode using the same ammeter. Special type of packaging is required to operate the photodiode in dual mode and the technique is not in general limited to the use of self-induced photodiodes. However, if using a self-induced photodiode both approaches can be applied independently on the same device and the radiometric measurement of fundamental constants e/hc can be measured as a validation of the equivalence between the two independent methods. As these fundamental constants are three of the defining constants of the new SI, the dual-mode detector will provide a direct link between two practical primary radiometric measurement techniques and the SI.

The chipS∙CALe project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

The STAR-CC-OGSE System for Pre-flight Sensor Calibration
Paul Green, Sean Devlin, William Kingett, Nigel Fox – National Physical Laboratory, UK

ABSTRACT: Reliable characterisation and radiometric calibration of satellite sensors are critical to their optimal performance on-orbit. Only through a robust understanding of the instrument behaviour, performance and degradation mechanisms will the significant effort and expense invested into the flight hardware be fully exploited. The uses of satellite sensor data, with their increased use in long-term environmental monitoring and climate studies mean that the performance and data quality provided by a single sensor can no longer be considered in isolation but needs to be considered as a part of the international Earth Observation (EO) infrastructure and referenced to common standard, the SI. The drive for improved performance, together with the desire for inter-operability between sensors creates increased demands on the pre-flight characterisation and radiometric calibration of sensors and the facilities needed to undertake these activities.

Sensor pre-flight characterisation and calibration facilities, or optical ground support equipment (OGSE) test sensor performance over a few broad categories including: geometric performance/image quality, channel/band co-registration, spectral calibration/out-of-band rejection, radiometric calibration, polarisation sensitivity, non-linearity, non-uniformity response etc. The specific requirements of the sensor, determined by its footprint, FoV, spectral extent & resolution, nominal radiance and required sensitivity typically results in a bespoke OGSE needed to meet the specific sensor requirements. For large-scale multi-sensor series programmes, a bespoke solution may remain the preferred solution. However, for single/few unit explorer missions, commercial constellations and more agile sensor development programmes, the expense & post-use redundancy of a bespoke OGSE system may be prohibitive.

NPL has developed a universal OGSE facility, the Spectroscopically Tuneable Absolute Radiometric calibration & characterisation OGSE (STAR-CC-OGSE), a versatile facility for the radiometric calibration and characterisation of satellite sensors. The system is provided fully characterised, calibrated and performance verified, with an easy to use software interface that allows fully automated remote operation. The system can be installed at a customer cleanroom facility or operated at NPL with a customer-supplied sensor. The main components of the STAR-CC-OGSE system are:

  • A large aperture integrating sphere source for radiometric calibration
  • A collimated beam source, equipped with an interchangeable, position fine-tuneable feature field mask for optical performance characterisation
  • A CW laser allowing monochromatic continuous tuneability from 270 nm to 2700 nm, with a broadband (white light) source extending over the same spectral extent.
  • A vacuum-compatible SI-traceable radiance detector module containing both broadband photodiodes & a spectrometer, installable in TVAC at the sensor-under-test entrance aperture

The laser illumination interface to the large aperture radiance sphere, collimator beam source or direct to the feature field mask allows fully tuneable monochromatic illumination for all characterisation and calibration modes.

STAR-CC-OGSE is undergoing final performance testing, with delivery to an initial lease customer in Spring 2020. This paper will describe the STAR-CC-OGSE system, the outcome of the verification testing and system performance.

2:30 pm | Sensor Calibration and Testing for Hosted Small Satellite Payloads

Examining small satellite payload calibration testing processes and methods, including accuracy and precision, to discover ways to reduce cost and schedule while still meeting mission requirements

  • Discussions about how new calibration and testing techniques and equipment can be applied to meet mission requirements while maintaining small satellite cost and schedule constraints
  • Novel techniques and sources used to perform radiometric calibration of miniaturized payloads
  • Trade-offs between performing testing at the sub-system, ground, and/or on-orbit levels
  • Calibration planning for upcoming small sat missions
  • Opportunities to cross calibrate multiple copies of the same sensor when they view the same scene
  • Methods for more efficient, cost-effective small systems analysis, without degrading quality

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On-orbit Calibration Methodology for Planet SuperDove Satellites
Arin Jumpasut, Alan Collison, Ignacio Zuleta – Planet

ABSTRACT: Planet currently operates a constellation of over a hundred satellites that collect a current image of the Earth each day. These satellites were launched over several years and cover several evolutions in design. The latest design are the Superdove satellites. One of the key advancements is a new payload with eight spectral bands, six of which are interoperable with Sentinel-2 and two of which are unique. This presentation will describe the on-orbit calibration methodology developed for this new design, results of the initial calibration and highlight some of the future improvements going forward.

The Spectral Response of Planet Doves: Pre-launch Method and Results
Caroline Pritchett, Nicolas Smith, Arin Jumpasut, Juan Fernandez-Saldivar, Ignacio Zuleta – Planet

ABSTRACT: Planet currently operates the largest constellation of Earth observation satellites. Known as Doves, these satellites are multispectral imaging systems operating in the visible and near IR wavelengths. Over the years, Planet has been iteratively improving our payload hardware and ground calibration systems so our data can better provide meaningful insights to the remote sensing community. Our latest payload iteration, called SuperDove, is natively interoperable with Sentinel-2. With these payload advancements, enhanced calibration and characterization are necessary while still keeping cost down and the schedule agile. Here we detail the method and results of the pre-launch spectral characterization of SuperDove. We compare the sequential spectral improvements from Dove-Classic to SuperDove and the continued compatibility across payload iterations. Additionally, we demonstrate how extensive automation of the data collection and analysis allows for efficient and uniform pre-launch characterization across satellites.

Using Lunar Observations to Radiometrically Assess the CUMULOS’ Visible Camera
Spencer Farrar, David Moyer, Kelly Collett, Dee Pack – The Aerospace Corporation

ABSTRACT: With the proliferation of CubeSats operating commercial off-the-shelf (COTS) instruments, it is necessary to assess the operational and performance limitations inherent with these reduced-cost systems, to understand applicability to specific mission areas. One of these limitations, as it pertains to the weather and environmental remote sensing mission area, is the limited satellite volume to house on-board calibrators (OCs) which characterize the instrument’s calibration while in orbit. Since most, if not all, Visible/Infrared payloads on CubeSats do not implement OCs, the instrument’s precision and stability can be significantly degraded as compared to their more expensive counterparts, such as the National Oceanic and Atmospheric Administration (NOAA) Visible Infrared Imaging Radiometer Suite (VIIRS) or the United States Geological Survey (USGS) Landsat 8 instruments. To improve instrument calibration for these systems, radiometrically stable and well-known target sources can be used as on-orbit vicarious calibration targets, such as homogeneous Earth scenes and the Moon.

The Aerospace Corporation’s Weather Remote Sensing Systems (WRemSS) Office implementation of the RObotic Lunar Observatory (ROLO) model was applied for on-orbit radiometric assessment of Aerospace’s CubeSat Multispectral Observing System (CUMULOS) on NASA JPL’s Integrated Solar Array and Reflectarray Antenna (ISARA) CubeSat. ISARA is a 3U CubeSat launched 12 Nov. 2017 on Cygnus Orbital ATK CRS OA-8 with CUMULOS taking up ~1U of volume. CUMULOS was designed as a compact payload for testing low-cost commercial cameras for weather and Earth environmental monitoring. It can measure surface temperature, detect fires and other environmental hotspots, take cloud cover pictures, and provide nighttime lights imaging by using three compact cameras: a visible wavelength camera, a short-wavelength infrared camera, and a long-wavelength infrared system microbolometer camera. The payload consists of three optics and sensor pairs: a panchromatic, visible CMOS camera, a short-wavelength infrared InGaAs camera, and a long-wavelength infrared microbolometer camera. This paper we will describe the CUMULOS instrument, present our radiometric stability assessment of the visible CMOS camera using the ROLO model, trending of dark field subtraction, anomalies, and lessons learned.

A Radiometrically Calibrated CubeSat Sensor: CUMULOS
John Santiago, Dee Pack, Ray Russell – The Aerospace Corporation; Richard Rudy – Kookoosint Scientific

ABSTRACT: The CubeSat Multispectral Observing System (CUMULOS) was a three-camera secondary payload that flew on the Integrated Solar Array and Reflectarray Antenna (ISARA) 3U CubeSat mission, with the goals of researching the use of commercial cameras for Earth remote sensing, and demonstrating unique nighttime remote sensing capabilities. CUMULOS was deployed on 6 December, 2017 by the Cygnus CRS OA-8E mission into an approximately 450-km circular 52° inclination orbit. After the successful conclusion of the primary ISARA mission, the CUMULOS payload was activated and achieved first light on 11 June, 2018. The CUMULOS mission ended a bit over a year later, when battery charging and power systems limitations prevented new imaging experiments from being performed, after the last successful collect on 15 June, 2019. Three separate cameras comprised the CUMULOS payload: 1) a visible ON Semiconductor (VIS) Si CMOS camera, 2) a FLIR Tau SWIR thermoelectrically stabilized shortwave infrared (SWIR) InGaAs camera, and 3) a FLIR Tau 640 longwave infrared (LWIR) vanadium oxide microbolometer. A critical part of the CUMULOS mission was investigating how the three relativity inexpensive commercial, off-the-shelf (COTS) focal planes and associated cameras would perform in a variety of nighttime related settings to produce high quality imagery and radiometrically calibrated images if possible. The three sensors had nadir ground sample sizes of 133, 450, 306-m for VIS, SWIR and LWIR respectively. Ground-based calibration measurements were performed on the CUMULOS cameras, the first of our cubesat sensors on which we attempted radiometric calibration. Issues associated with this first-time effort led to a non-ideal state of the ground (pre-launch) calibration. This paper will briefly outline what was attempted on the ground, but will primarily focus on what calibrations were performed on orbit to allow radiometric calibration to be completed. The on-orbit activities included: 1) combining observations and models of stars α Tau and α Lyra to derive irradiance responsivity values, and to derive radiance responsivity calibration terms, 2) programming dithers into stellar calibration experiments to improve background subtraction to find dim objects, and 3) augmenting ground darks with very low exposure time images taken during collections, and/or dark deep space frames. It was typically found that the dark frames taken on orbit were superior to dark frames taken on the ground only for the SWIR sensor. The SWIR sensor suffered from a high and growing number of hot pixels (radiation damage) that caused problems identifying stellar objects, and degraded science quality images. The LWIR calibration is still being worked. In this paper we will: 1) address the stellar calibration of the VIS and SWIR sensors on-orbit and compare different datasets to assess the accuracy and repeatability of those calibrations, 2) show how the SWIR sensor’s hot pixels changed and increased over time and the methods used to suppress them, and 3) present images taken by the CUMULOS VIS and SWIR sensors and compare them to VIIRS images of the same region at the same time.

This research was funded by The Aerospace Corporation’s Independent Research and Development program.

Hurdles for Getting Smallsat Data Sets into NOAA Operational Forecasts
B. Guenther – Stellar Solutions

ABSTRACT: Small satellite opportunities in the US and abroad have blossomed into what seems to be a boundless new Space Age. The infrastructure for building and launching small satellites has matured rapidly. One aspect that seems to be lagging is getting these datasets into operational weather forecasting applications. Within this exciting new world, with seemingly unbounded opportunities, one must wonder “What could go wrong.” Coming with an experience base on satellite missions spanning more than a half century now, starting with the Orbiting Geophysical Observatory – 6 in June, 1969, the author of this presentation will offer some examples of what could go wrong. Some instances would seem best solved by the Government for supporting these opportunities, and other instances would seem to require engineering solutions by the Smallsat community developers. Radiometric performance for Small Sat missions will get special attention. The ideas presented are solely the presenter’s point of view and do not represent any official positions of either NOAA or Stellar Solutions.

Wednesday, September 23, 2020

8:00 am | Pre-launch Testing and Post-launch Performance

Assessment of pre- and post-launch calibration and performance characterization for operational remote sensing systems

  • Pre-launch and on-orbit measurement techniques
  • Instrument transition from the laboratory to space environments
  • Application of ground calibration results to on-orbit measurements
  • Operational sensor calibration lessons learned

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Decoupling Flat-fielding and Non-linearity Correction of a Pushbroom Radiometer – Analysis of Landsat 9 Operational Land Imager-2 Prelaunch Test Data
Raviv Levy – Science Systems and Applications Inc. / NASA Goddard Space Flight Center; Brian Markham – NASA

ABSTRACT: One of the goals in any calibration effort for pushbroom imaging radiometers is to flat field the instrument data across the full dynamic range. A challenge when approaching levels of 1% and lower in a 14 bit system is that the non-uniformity and non-linearity become a coupled variable set. The Landsat-9 Operational Land Imager-2 (OLI2) prelaunch radiometric calibrations conducted at Ball Aerospace utilized spectral sources, large integrating spheres and rotation stages. These tools, combined with unique collects such as the integration time sweeps and yaw collects at multiple illumination levels provided the basis for improvements in the calibration of both the full field of view and the full dynamic range for all of spectral bands. In an integration time sweep, a constant source level is observed while varying the detectors’ integration time; in a yaw collect the instrument is rotated so that each detector views the same part of the illumination source. While previously we reported on the characterization of the calibration source used, this presentation will focus on how the multiple datasets were utilized to arrive at flat fielding and the non-linearity corrections. The method used enables a reduction in the uncertainty of the uniformity correction throughout the dynamic range. The uncertainty in the source non-uniformity, the source stability and the instrument under test stability are the three limiting factors. The data sources, the types of non-linearities, the differences between integration time sweeps and radiance collects, the representations of the non-linearity and the validation of the relative gain corrections throughout the dynamic range will be presented.

Pre-launch Radiometric Calibration of the JPSS-2 OMPS Instrument
Tyler McCracken, Eileen Saiki, Thomas Rogers, Dan Soo – Ball Aerospace

ABSTRACT: Ball Aerospace and Technologies Corp. has built the third build of the Ozone Mapping and Profiler Suite (OMPS), which measures daily ozone using three spectrometers that cover a wavelength range from 250 nm to 1000 nm. The JPSS-2 OMPS instrument consists of a pair of nadir-viewing spectrometers that provide total column ozone measurements and a limb-viewing spectrometer that provides ozone vertical profiles. The ground radiometric calibration of the sensors is ultimately albedo-based and determined through a sequence of tests to determine both absolute calibration and a direct albedo calibration. This presentation discusses the results of the JPSS-2 OMPS ground calibration program including an overview of the test suite and calibration uncertainties.

Ground-to-Space Transmitter System for Extended Instrument Diagnostics of On-Orbit Operational Radiometric Sensors
Timothy Berkoff, Constantine Lukashin, Trevor Jackson, Carlos Roithmayr – NASA Langley Research Center; William Carrion – Science Systems and Applications, Inc. (SSAI) / NASA Langley Research Center; Steven Brown, Brian Alberding – National Institute of Standards and Technology (NIST); Tom Varghese – Cybioms, Brendan McAndrew, Jan Mcgarry, Evan Hoffman, Mark Shappirio, Joel McCorkel – NASA Goddard Space Flight Center; Vanderlie Martins – University of Maryland, Baltimore County

ABSTRACT: Satellite instrument change in orbit during a mission lifetime can result in significant error for absolute radiance sensor calibrations. Polarization (POL) response, out-of-band signal rejection (OOB), and relative spectral response (RSR) are important contributors to understanding calibration error, yet no existing systems can conduct all of these diagnostics while a sensor is in space. In this presentation, a system under development is described that enables new diagnostic analyses of radiometers while they are in orbit by propagating a laser beam from the ground. While the system is not expected to provide high accuracy (<7%) absolute radiance calibrations, it is anticipated to provide POL, OOB, and RSR characterization measurements at high precision and repeatability, as these are self-referenced measurements and do not require knowledge of absolute radiance arriving at the sensor. The approach we are investigating will propagate a specially conditioned multi-beam phase-scrambled continuous wave laser transmission designed to mitigate atmospheric and laser coherence effects. To conduct a measurement, the space-borne sensor would need to “point-and-stare” at a pre-determined ground-target location. The ability to evaluate POL, OOB, and RSR changes during a mission enables critically needed insights to the cause of calibration change of current and proposed mission sensors. To achieve the same diagnostic capabilities with on-board hardware would be inherently prohibitive due to expense, increase in complexity, power, size, and payload mass. Understanding calibration change is especially important for trend analyses of Earth observations, where continuity of data sets and time on orbit needed to reach a scientific conclusion is at a premium. In addition, this approach can potentially reduce the need for additional complex on-board calibration systems on future missions, resulting in long-term cost savings and risk reduction for satellite operations. For small-size satellite platforms, such as U-class CubeSat systems, the Ground-to-Space Laser approach could enable critical diagnostic capability in cases where on-board diagnostic systems are not possible.

GOES-17 ABI L1b Product Performance Mitigation Results
Jon Fulbright – ASRC Federal; Elizabeth Kline – NOAA/NESDIS/GOES-R; David Pogorzala – Centauri; Katherine Pitts – Science Technology Corp; Zhipeng Wang, Xiangqian Wu – NOAA/NESDIS/STAR

ABSTRACT: The ABI instrument on GOES-17 suffers from insufficient cooling, resulting in degradation in the L1b radiance products during times of excessive solar heating. The original calibration algorithm assumes only a slowly-varying thermal state, and the primary calibration parameters, the gain and offset values, become obsolete almost immediately during times of rapid thermal changes.

In July 2019 a modification of the calibration algorithm (named “Predictive Calibration”) was introduced as part of the mitigation strategy. We described this algorithm last year at Calcon, and now we have on-orbit data quantifying the improvement. In this talk, we summarize the early evaluation of L1b products created with this modified algorithm. We also describe some of the imagery artifacts sometimes introduced into the GOES-17 ABI L1b data by the Predictive Calibration or other mitigation steps.

Focus Characterization and Performance of Planet’s SuperDoves On-ground and On-orbit Performance Predictions
Juan Fernandez-Saldivar, Caroline Pritchett, Kenji Ozawa, Ignacio Zuleta – Planet

ABSTRACT: Consistent imaging performance of Planet’s SuperDoves is a key feature as the main goal is for global daily revisits over Earth’s landmass. For such small 3-U cubesat platforms, the thermal environment imposes unique challenges in ensuring the payload remains in focus over not only repeated orbital conditions but other varying operational conditions (downlinks and other pointing manoeuvres).

The modelling and testing on ground of representative space thermal environments is typically done using extensive tests. Whilst this is a common approach of larger platforms and fewer satellites, the variability of the large number of satellites, conditions and dynamics will be prohibitive to perform fully for each satellite in a typical Planet’s constellation. In order to account for the satellite to satellite variability Planet has approached this challenge by reducing the set of on-orbit conditions to a relatively small subset of thermal tests that can be carried out not only on each full satellite but also at the telescope level in air. This is leveraged by quick iteration in production and including automation for test and analysis of results.

In this work, we compare some of the satellites on 2 flocks already on-orbit by relating them to their ground focus test results and to other telescopes which are currently being tested and that will be launched later on this year. Using this approach Planet quickly iterates in assessing and predicting the behaviour of the image performance and variance across flocks and ensure that satellites will be in focus for operational conditions.

Radiometric Calibration Performances of GOES-16/17 Advanced Baseline Imagers
Fangfang Yu, Hyelim Yoo, Zhipeng Wang, Haifeng Qian, Xi Shao – University of Maryland; Xiangqian Wu – NOAA/NESDIS/STAR

ABSTRACT: The Advanced Baseline Imager (ABI) is the primary instrument onboard NOAA’s current Geostationary Operational Environmental Satellites (GOES), GOES-16 (GOES East) and GOES-17 (GOES West). These 16-band instruments are collecting imagery critical to the National Weather Service for accurate weather nowcasting and forecasting over the Earth’s Western Hemisphere. While GOES-16 operates as designed, the partial failure of the GOES-17 ABI cooling system leads to a set of different operational configurations that optimizes the instrument performance under the circumstances. Since GOES-17 ABI became operational in February 2019, several major Ground System (GS) updates have been successfully implemented to improve the ABI radiance quality of the solar reflective and infrared (IR) bands. The impacts of the GS updates on radiance and image quality were intensively validated and carefully monitored using different methods. This study is to report the radiometric calibration performance after each major update. The update of the scan mode in April 2019 reduces the calibration difference between the swaths within the timeline for the GOES-17 IR bands. The predictive calibration (pCal) algorithm implemented in July 2019 significantly improves the calibration accuracy for the GOES-17 IR data when they are available during the period of unstable focal plane module (FPM) temperature, and thus greatly reduces the calibration error at night. After several solar calibration updates to both ABIs from April to June 2019, the overall difference is less than 5% for all the solar reflective bands as compared to the corresponding channels of S-NPP Visible Infrared Imaging Radiometer Suite (VIIRS). Details will be reported in the meeting.

NEON Imaging Spectrometer (NIS) Calibration Updates
Alok Shrestha, Tristan Goulden, Ian Crocker – Battelle; Joe Boardman – AIG LLC

ABSTRACT: The NIS (NEON Imaging Spectrometer) is an airborne pushbroom hyperspectral instrument developed by NASA Jet Propulsion Laboratory (JPL) for the National Ecological Observation Network (NEON) and is included in all three of NEON’s Airborne Observation Platform (AOP) payloads. NEON, funded by the National Science Foundation (NSF), is a continental-scale observatory designed to collect long-term data to better understand and forecast impacts of climate change, land use change and invasive species (Kampe et al. 2010). NEON has recently completed the construction phase and is in the initial operational phase, which represents annual activities that will be repeated for the remaining 30-year lifetime of the project (Goulden et al. 2019). The AOP begun data collection in 2013, although only a small subset of NEON sites was collected. By 2018 and 2019, AOP was collecting data in 16 domains annually, representing the typical data collection scenario during the operational phase of the NEON project. NEON provides 28 data products from AOP, which are publicly available and can be freely accessed from NEON data portal: In addition to the NIS, AOP payloads include a discrete and full-waveform lidar and a high resolution RGB camera.

The NIS design is based on AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) NextGen Imaging Spectrometer and measures radiant energy both in VNIR (Visible-Near Infrared) and SWIR (Shortwave Infrared) spectral region (380-2510 nm) with ~5 nm sampling and 1 mRad instantaneous field of view (IFOV) (Kuester et al. 2010). This 1 mRad IFOV leads to a ground resolution of 1m at a typical flight altitude of ~1000m. In order to ensure the accuracy of the measurements, the NIS requires stable and consistent annual calibrations (Leisso et al. 2014). Assessment of NIS calibration datasets revealed anomalies that should be characterized and corrected to improve the accuracy of NIS datasets. This presentation will briefly discuss the current status of NEON project and provides detailed description of NIS calibration improvements including: 1) characterizing NIS stray light anomalies, 2) techniques implemented to correct such anomalies, and 3) NIS stability analysis.

Goulden T., B. Hass, J. Musinsky, and A. K. Shrestha, 2019, "Status of NEON's Airborne Observation Platform", AGU Fall Meeting, 9-13 December, 2019, San Francisco, CA, USA,
Kampe T. U., B. R. Johnson, M. Kuester, and M. Keller, 2010, "NEON: the first continental-scale ecological observatory with airborne remote sensing of vegetation canopy biochemistry and structure", Journal of Applied Remote Sensing 4(1), 043510 (1 March 2010).
Kuester M. A., J.T. McCorkel, Johnson, B.R., and Kampe T.U., 2010, "Radiometric Calibration Concept of Imaging Spectrometers for a long-term Ecological Remote Sensing Project"
Leisso N., Kampe T., Karpowicz B., 2014, "Calibration of the National Ecological Observatory Network's airborne imaging spectrometers", 2014 IEEE Geoscience and Remote Sensing Symposium, Quebec City, QC, 2014, pp. 2625-2628. doi: 10.1109/IGARSS.2014.6947012

2:15 pm | Equipment, Capabilities, and Facilities for Radiometric Calibration

Hardware and resources to support National and international requirements for radiometric calibration of remote sensing instruments, including long-term trending and performance enhancements of existing facilities.

  • Design, characterization, and validation of test and calibration equipment, facilities, test chambers, and scene simulators (Earth, solar, and other objects)
  • Scene generation and projection for hardware-in-the-loop (HIL) testing
  • Specialized measurement equipment (spectral, polarization, and other)
  • Long- and short-term accuracy and precision of data sources used for validation, including models
  • Novel techniques, algorithm technologies, and processes to support and enhance the way we approach radiometric calibration

Live event has ended View Abstracts (PDF)

A Generalized Combinatorial Technique for Linearity Calibrations Applied to Optical Detectors and Spectrographs
Howard Yoon – National Institute of Standards and Technology (NIST)

ABSTRACT: For many quantities, indicating instruments are calibrated only at a limited number of values, and the extension of the calibrations to higher or lower values must rely upon the linearity of the instruments.  A method for calibrating or determining the linearity of instruments that exploits the combinatorial properties of a set of different-valued, and mostly uncalibrated, artefacts is described. The presentation describes the underlying principles of the method, its limitations, and examples of the application of the method to very different quantities: mass balances, resistance bridges, optical detectors and spectrographs. The resulting uncertainty due to linearity can be assigned from the residuals of the fitted functional form of the linearity function to the measured signals.

The implementation of this combinatorial method with the NIST Beamconjoiner apparatus is described, and calibrations of visible and infrared photodiodes, and spectrographs for internal and external customers are shown. This method is shown to be capable of determining linearities in the visible and infrared wavelength region to uncertainties of 200 ppm or 0.02 % (k=2). Linearities of spectrographs at a set integration time and as a function of integration times can be measured using this approach. Experimental setups to characterize focal plane arrays placed in cryo-vac chambers will be discussed.

Characterization of Fluorescence from the GLAMR 30” Integrating Sphere
Brendan McAndrew, Joel McCorkel – NASA Goddard Space Flight Center; Julia Barsi, Yigit Aytac – Science Systems and Applications, Inc. (SSAI); Tim Shuman – Fibertek

ABSTRACT: The Goddard Laser for Absolute Measurement of Radiance (GLAMR) has been used to provide spectral and radiometric calibration data for several earth science instruments, including the Joint Polar Satellite System (JPSS) -2 and -3 Visible and Infrared Radiometer Suite (VIIRS). Analysis of data collected by both VIIRS instruments has suggested the presence of fluorescence emitted from the GLAMR integrating sphere when illuminated by visible and ultraviolet light. This takes the form of an unexpected out of band response below 550 nm in several VIIRS bands that is in addition to interband electronic crosstalk. The VIIRS spectral response is also characterized by a monochromator which does not replicate the higher out-of-band response but has reduced dynamic range.

As a result of the VIIRS data analysis, additional characterization of the GLAMR integrating sphere have been performed specifically to check for fluorescence in the visible and near infrared range by illuminating the sphere with visible and near ultraviolet monochromatic light. The broad band spectrum of radiance generated by the integrating sphere is measured using a calibrated spectroradiometer at 3 nm spectral resolution with high SNR at a factor of 10-4 of the radiance of the primary illumination wavelength. This allows for out of band characterization down to the noise floor of previous VIIRS testing. This spectrum is correlated with the VIIRS data sets as well as other instruments calibrated using the same integrating sphere. Prior instrument data also allows some check of the stability of the fluorescence signal over time.
The characterization of the fluorescence will allow it to be accounted for in analysis of flight instrument spectral responses and improve the overall accuracy of the GLAMR characterization.

Initial Results of FLARE Network Vicarious Calibration Method
Christopher Durell, Brandon Russell, Dan Scharpf, Jeff Holt, Will Arnold – Labsphere, Inc.; David Conran – RIT; Stephen Schiller – Raytheon, Inc.

ABSTRACT: Labsphere has created automated vicarious calibration sites using the SPARC mirror technology in the new FLARE network. A short introduction to the FLARE network will be given. This paper will describe the system construction, function and implementation of the initial sites. Campaign information for small and large satellites were carried out and results of these events will be cataloged. Uncertainty models and data has been evaluated against Landsat 8 and Sentinel 2A and 2B and preliminary results will be presented.

Development of a Collimated Large Area Uniform Light Source for the Measurement of Solar Diffuser BRDF in Support of NASA Satellite Instrument Programs
Jinan Zeng – Fibertek, Inc. at NASA Goddard Space Flight Center

ABSTRACT: We report the development of a collimated large area uniform light source, which is used to acquire diffuser BRDF measurements in support of the pre-launch calibration of NASA Earth observing satellite instrument. In accordance with the goal of “testing as you fly,” this large area light source permits the measurement of diffuser BRDF using illumination geometrically similar to that realized on orbit. In the design and testing of this source, several approaches using different light sources and collimating optics were examined with the overarching goal of producing a monochromatic, unpolarized large area, uniform, collimated beam with sufficient throughput power to enable BRDF to be measured. The major components of the collimated large area uniform light source employ a series of high-power LEDs from UV-VIS to SWIR with or without an integrating sphere. Light from this source is coupled to either a 30.48 cm diameter size off-axis parabolic mirror (OAP) or a 45.72 cm diameter spherical concave mirror. A large beam uniformity evaluation system employing a scanning detector was used to measure light source uniformity. In this presentation, we describe our approaches to produce large area uniform solar diffuser illumination, and discuss potential technical difficulties. Since technical challenges exist in achieving the 1% uniformity in a collimated large area light source, we also propose a correction method to mitigate non-uniformity using a laser scan method. The characterization of the collimated large area uniform light source and preliminary BRDF results are presented.

Thursday, September 24, 2020

8:00 am | Space Station Instruments

Examine the unique challenges and advantages associated with International Space Station (ISS) payload design, calibration, and operation.

  • Completing science objectives within the time allocated on the ISS
  • Special materials and contamination considerations
  • Unique ground test and calibration requirements
  • Space station-specific concept of operations

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Radiometric Cross-Comparison of DESIS with Landsat 8 OLI and Sentinel 2A MSI
Mahesh Shrestha, Jon Christopherson – U.S. Geological Survey Earth Resources Observation and Science (EROS) Center

ABSTRACT: The DLR Earth Sensing Imaging Spectrometer (DESIS) is a new hyperspectral instrument developed by the German Aerospace Agency (DLR) and operated under the collaboration of DLR and Teledyne Brown Engineering (TBE). It is mounted on International Space Station (ISS) and has a ground sample distance of 30 m and a swath of 30 km. It has 235 spectral channels that measure across the spectral range from 400 nm and 1000 nm with a spectral sampling of approximately 2.5 nm. This study performs the radiometric assessment of DESIS by cross comparing it with a well-calibrated sensor such as Landsat 8 Operational Land Imager (OLI) and Sentinel 2A Multispectral Instrument (MSI). The cross-comparison between DESIS and Landsat 8 OLI and Sentinel 2A is performed by using the three and two coincident collects between the sensor pairs respectively. From these three coincident collects between DESIS and Landsat 8 OLI, 17 regions of interest (ROI’s) of different surface types and intensity levels are chosen for cross-comparison. Initial analysis shows that there is a very good agreement between DESIS with Landsat 8 OLI. The mean of reflectance difference between DESIS and Landsat 8 OLI is within 0.015 reflectance unit and approximately 7% (in relative scale) across all the bands. Similarly, for DESIS and Sentinel 2A cross-comparison, two coincident collects from Libya 4 CNES ROI are used. The difference between these two sensors is within the 0.015 reflectance unit across all the bands. These initial results show that DESIS has a very good agreement with both Landsat 8 OLI and Sentinel 2A MSI.

Atmospheric Waves Experiment Calibration
Joel Cardon, Harri Latvakoski, Greg Cantwell – USU/Space Dynamics Laboratory

ABSTRACT: The Atmospheric Waves Experiment (AWE) is the first dedicated NASA mission to investigate global gravity wave properties in the upper atmosphere and their impacts on the ionosphere-thermosphere-mesosphere (ITM). The AWE Advanced Mesospheric Temperature Mapper (AMTM) will fly on the ISS and measure temperature waves in the OH airglow layer. The OH temperature waves are produced by gravity waves that rise from the Troposphere into the Mesosphere and spread out horizontally in the OH airglow layer at ~87km altitude, carrying energy and momentum with them. The temperature waves are observed by measuring the background-subtracted ratio of OH P1(2) and P1(4) emission line radiances. The AWE calibration will be performed at SDL in the large THOR chamber using collimator and extended blackbody sources. The AMTM has a very large 90° field-of-view, and the ground calibration must be performed over this full range, requiring a 2-axis gimbal platform in the THOR chamber. This paper will summarize ISS-specific challenges and ground and on-orbit calibration plans.

Improved Radiometric Accuracies for Climate Science with HySICS
Greg Kopp, Paul Smith, Peter Pilewskie – Laboratory for Atmospheric and Space Physics (LASP), University of Colorado; Gary Fleming, Bruce Wielicki – NASA Langley Research Center

ABSTRACT: The HyperSpectral Imager for Climate Science (HySICS), to be flown as the CLARREO Pathfinder payload in 2023, will acquire images of the Earth’s ground and atmosphere with unprecedented radiometric accuracies of <0.3% (k=1) achieved via on-orbit calibrations using the spectral solar irradiance. These high radiometric accuracies enable benchmarking of Earth radiances for climate studies and provide reference calibrations for other on-orbit Earth-viewing sensors.

The 2007 U.S. Academy of Sciences Decadal Survey for Earth Science recommended the Tier 1 mission CLARREO (Climate Absolute Radiance and Refractivity Observatory) to acquire high-accuracy, climate-benchmarking spatial/spectral radiances of the Earth's surface and to provide reference calibrations for other on-orbit assets. The more recent 2018 Decadal Survey similarly prioritized reference radiance inter-calibrations as one of its "Most Important Targeted Observables," providing on-orbit SI traceability for other programs such as the Global Space Based Inter-Calibration System (GSICS). To achieve these climate-benchmarking and inter-calibration capabilities, the space-borne imaging spectrometer for the CLARREO requires radiometric-accuracies that are nearly 10x better than any currently-flying spectrometer provides, necessitating innovative new on-orbit measurement techniques.

The HySICS is currently in development for the NASA CLARREO Pathfinder, a mission planned for launch to the International Space Station (ISS) in 2023 to demonstrate both the CLARREO-needed on-orbit radiometric accuracies and inter-calibrations of other space-based sensors. The instrument has a radiometric-uncertainty goal of 0.3% (k=1), which is much better than any current spaceflight reference detector or calibration light source is capable of providing. Instead of incorporating either of these traditional detector- or source-based calibration approaches into the instrument, the HySICS relies on on-orbit calibrations provided by direct views of the spectral solar irradiance, which is known on an absolute scale to ~0.2% from other space-based instruments. As opposed to using diffusors or other scattering surfaces that can degrade on orbit, the HySICS is designed for improved radiometric accuracies by regularly acquiring direct solar-irradiance measurements, avoiding concerns with on-orbit degradation that plague Earth-sensing optical instruments. A prototype HySICS demonstrated this solar-irradiance cross-calibration approach during two high-altitude balloon flights (Kopp et al., 2017).

We describe the radiometric-accuracy details of this Offner-based imaging spectrometer that contiguously covers 350 to 2300 nm with 6-nm spectral resolution and has an instantaneous nadir-looking field-of-view of 500 m and a swath width of 70 km from the ISS's orbit altitude.