Technical Sessions

Tuesday, August 22, 2017

1:10 pm | 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

Session Chair: Jack Xiong, NASA Goddard Space Flight Center

View Abstracts (PDF)

Removing Radiation-Induced Spikes from Fourier Transform Data
Mark Esplin, Ben Esplin, Deron Scott – USU/Space Dynamics Laboratory

ABSTRACT: A common problem with space-based sensors is sharp spikes in the signal caused by ionizing radiation striking the detectors or analog signal chain. To minimize the spectral corruption caused by these spikes, a new spike correction method has been developed for the Cross-track Infrared Sounder (CrIS) on the Suomi National Polar-orbiting Partnership (SNPP) spacecraft. CrIS is an infrared, Fourier transform spectrometer used to make weather and climate observations. Radiation-induced spikes are a particularly serious problem for Fourier transform spectrometers since a single spike in the interferogram will cause corruption throughout the entire length of the spectrum. For CrIS, a spike large enough to cause a pixel to be flagged as invalid happens every few days. However, a number of smaller spikes that cause corruption but are not sufficiently large to be detected by the present quality control software happen daily.

The CrIS sensor was launched with a simple onboard spike correction method that set any interferogram samples above a given threshold to zero. This method did not take into account interferogram offsets and low frequency drifts. As a result, it caused more errors than it corrected and has been mostly disabled by setting the threshold to a very high value. The new ground-based correction method was subsequently developed to remove interferogram spikes. This algorithm works by modeling a radiation spike then subtracting the modeled spike from the interferogram that contained the spike. The radiation event is much faster than the detector electronic, so the shape of the spike is determined by the electronic response of the electronics. The amplitude and position of the spike is determined from a least-squares fit to the interferogram data. The spikes occur in the raw interferogram, but to reduce bandwidth, the digitized interferograms are processed with a Finite Impulse Response (FIR) filter and decimated before being transmitted to the ground. The filtering and decimating process spreads and alters the appearance of the original spike. However, since the FIR filtering and decimating process is linear, it is possible to perform a least-squares fit between the filtered and decimated interferogram containing a spike and a modeled spike that has also been filtered and decimated. Once the amplitude and position of the spike have been estimated, the effects of the spike can readily be calculated and subtracted from the original interferometer. The method has been very successful in removing spikes and is presently being evaluated for inclusion into the operational CrIS ground processing software.

GOES-R ABI Emissive IR Bands Radiometric Performance Monitoring and Trending
Haifeng Qian, Boryana Efremova, Robert Iacovazzi, Fangfang Yu, Xi Shao – ERT, Inc.; Xiangqian Wu – NOAA STAR

ABSTRACT: The first of a new generation of imaging instruments - the Advanced Baseline Imager (ABI) was launched aboard the first of the Geostationary Operational Environmental Satellites – R Series (GOES-R), currently named GOES-16, on November 19 2017. The main payload instrument on-board is Advanced Baseline Imager (ABI), which has 16 multi-spectral bands covering the spectrum between 0.47µm and 13.3 µm to provide continuous data stream for weather forecasting, disaster monitoring, and long-term climatic change studies. This instrument ABI is housed a temperature-controlled blackbody to provide accurate on-orbit radiometric calibrations in thermal infrared (IR 3.9-13.3 μm) spectral regions from the band 7 to band 16, respectively. After launch, it is urgent and critical to monitor and evaluate the instrument calibration performance in a timely manner on these IR bands with the data from the ground segment system, especially during the Post-Launch Tests (PLT) and Post-Launch Product Tests (PLPT). After PLPT, the importance still continues in real-time monitoring and long term trending. For this purpose, we develop an informative monitoring and trending system for GOES-R ABI radiometric performance in thermal infrared IR band 7-16. The monitoring and trending includes direct counts, gain, offset, noise equivalent change in radiance (NEdN), noise equivalent differential temperature (NEdT), and dynamic range characterization from minutes to all-life timescale, from the sample, detector level to L1B pixel level, as well as some other aspects of the instrument performance such as ABI image swath banding, band-dependent striping identification etc. This system thus does not only make the user well informed the improvement of ground segment system implementing the updates in thermal infrared IR bands, but also provides the clues for the anomalies resolving. At the same time, the statistics analysis of the Internal Calibration Target (ICT) and space-look counts on sample/detector/pixel level in different timescales from GOES-R calibration working group (CWG) in comparison with the ground segment system processing, are also presented in this monitoring and trending system.

Calibration/Validation Activities and Status for GOES-16 Products
Jon Fulbright – Arctic Slope Technical Services; Elizabeth Kline – Science and Technology Corporation; David Pogorzala – Integrity Applications Incorporated; Kathryn Mozer, Wayne MacKenzie, Matthew Seybold – NOAA/OSPO

ABSTRACT: The Geostationary Operational Environmental Satellite-R series (GOES-R) will be the next generation of NOAA geostationary environmental satellites. The first satellite in the series, GOES-16, was in November 2016. The satellite carries six instruments dedicated to the study of the Earth’s weather (ABI), lightning mapping (GLM), solar observations (EXIS and SUVI), and space weather monitoring (MAG and SEISS). Since launch, a series of Post-Launch Test and Post-Launch Product Tests have been conducted to validate, calibrate, and characterize both the instruments and the data products. By August 2017, the product calibration/validation and instrument characterization plans for the L1b data products of these six instruments should be nearing or past the Provisional product maturity threshold. These cal/val plans were created to advance the products through well-characterized states following an aggressive maturity schedule. In this talk, we describe some of the major cal/val activities that have taken place since launch, focusing mainly on ABI and GLM. We also give an update of the status of the GOES-16 products, the path forward to Full product validation status, and a look forward to any changes to the cal/val plans GOES-S (to be launched in 2018).

Radiation Budget Instrument Final Design and EDU Calibration Test Results
Ronald Glumb, Jay Overbeck, Christopher Lietzke, John Forsythe, Jason Miller – Harris Space and Intelligence Systems

ABSTRACT: For the past three decades, the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) instruments have established a long-term data record for the total radiance being emitted and reflected from the Earth. This data record is critical to understanding the Earth’s radiation balance, which in turn is a key driver of seasonal weather and long-term climate measurements. The Radiation Budget Instrument (RBI) will continue the ERBE/CERES data records into the future.

RBI measures upwelling Earth radiance over an extremely broad spectral range, from the ultraviolet (0.3 microns) to the far-infrared (100 microns), separated into three spectral bands. RBI includes advanced onboard calibration subsystems which provide the exceptionally precise radiometric uncertainty (with requirements of approximately 0.5%-1.0%) and repeatability (with requirements less than 0.25%) needed to fulfill the radiation balance mission.

RBI’s first flight will be on the JPSS-2 satellite, which is planned for launch in 2021. RBI has recently completed its Critical Design Review (CDR), and testing of an Engineering Development Unit (EDU) is underway. This paper will describe final design of the RBI flight instrument and provide the latest projections for the radiometric and spectral performance of the instrument. In addition, test results from the EDU prototype will be discussed in detail.

Progress of S-NPP VIIRS Reflective Solar Calibration
Jack Xiong – NASA Goddard Space Flight Center

ABSTRACT: The S-NPP VIIRS has successfully operated for more than 5 years since its launch in October, 2011. Including a day-night band (DNB), the VIIRS collects data in 22 spectral bands, covering wavelengths from 0.4 to 12.4 um. On-orbit calibration of its reflective solar bands (RSB),is performed using a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system. In addition, regularly scheduled lunar observations are used to support RSB on-orbit calibration. In this paper, we provide an overview of S-NPP VIIRS reflective solar calibration activities, methodologies, and progress made from launch to present with a focus on the efforts made by the NASA VIIRS Characterization Support Team (VCST). Topics will include RSB (and DNB) calibration strategies by combining the data collected from on-board SD, the Moon, and selected stars. Also illustrated in the paper are examples of VIIRS RSB on-orbit calibration performance since launch, remaining challenges, and future work in order to maintain and further improve its calibration and data quality.

Capability Enhancements, Changes, and Limitations of Joint Polar Satellite System (JPSS) -1 Compared to Suomi-National Polar-orbiting Partnership (S-NPP)
Cole Rossiter, Bruce Guenther – Stellar Solutions, Inc.

ABSTRACT: Joint Polar Satellite System (JPSS) -1 is the first of four next-generation, polar-orbiting weather and environmental monitoring satellites currently slated to launch on September 21, 2017. JPSS-1 features technology first tested operationally on the Suomi-National Polar-orbiting Partnership (S-NPP), which is a risk-reduction inter-program mission launched on October 28, 2011. In addition to the spacecraft, this technology includes five instruments: the Advanced Technology Microwave Sounder (ATMS), the Cross-track Infrared Sounder (CrIS), the Visible Infrared Imaging Radiometer Suite (VIIRS), the Ozone Mapping and Profiler Suite (OMPS), and the Clouds and the Earth’s Radiant Energy System (CERES). The two will share identical orbit dynamics including a nominal altitude of 824 +/- 17 km, a ground track repeat accuracy of +/- 20 km at the Equator, a ground track repeat cycle of 16 days, and a local time ascending node (LTAN) of 1330 +/- 10 minutes. The two satellites will be separated by half an orbit (~50 minutes) during nominal operations. JPSS-1 will provide critical, near-real time data inputs to National Weather Service (NWS) models, improve forecasting in the Alaskan region, and extend the 30+ year continuous history of climate data records collected by remote sensing satellite technology. The purpose of this presentation is to highlight the capability enhancements, changes, and limitations of JPSS-1 compared to S-NPP.

Enhancements include the addition of a Ka band transmitter, twice per orbit ground station data links, new ATMS scan drive bearings, VIIRS DNB stray light, and improved OMPS Nadir Profiler (NP)/Total Column (TC) resolution. Changes include the incorporation of all data into the HRD data stream, ATMS SDR data reported in radiance versus brightness temperature, CrIS full spectral resolution and VIIRS M11 at night in the at-launch product baseline, reduction in VIIRS scan sync loss susceptibility, and no OMPS Limb instrument. Limitations include the lack of ATMS flight configuration spectral response functions (SRFs) taken after ATMS rework, VIIRS scan-to-scan underlap in the equatorial region, and increased VIIRS polarization in the ocean color bands.

Wednesday, August 23, 2017

8:00 am | 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

Session Chair: Tom Stone, U.S. Geological Survey (USGS)

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Calibration Acquisitions Of and Using the Moon by CLARREO Pathfinder
Tom Stone – U.S. Geological Survey; Constantine Lukashin – NASA Langley Research Center; Greg Kopp – University of Colorado Laboratory for Atmospheric and Space Physics (LASP)

ABSTRACT: The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a Tier 1 mission recommended by the 2007 NRC Earth Science Decadal Survey. The mission's technical objectives are to acquire high-accuracy SI-traceable decadal length Earth observations for climate records and to enable reference inter-calibration of other Earth observing sensors. The CLARREO Pathfinder (CPF) project has the key objective to demonstrate essential shortwave measurement technologies required for the full CLARREO mission. In January 2017, the CPF mission began formulation Phase-A. CPF will operate a Reflected Solar (RS) spectrometer to be launched in the 2021 timeframe to the International Space Station (ISS). The RS instrument will have contiguous spectral coverage from 350 nm to 2300 nm, with the science objective for absolute uncertainty < 0.3% (k=1). In addition to its primary purpose of acquiring Earth ground scenes, the CPF will observe the Moon when viewing opportunities are available from its mounting location on the ISS ExPRESS Logistics Carrier (ELC-1), Site 3. These observations will acquire above-atmosphere spatial/spectral measurements of the lunar disk at varying phase angles to be used for verifying sensor response stability, and also along-slit scans to be used for instrument flat-fielding. Given the accuracy goals of the RS instrument, the CPF radiometric measurements of the Moon may be used to improve the lunar spectral irradiance calibration standard, which in turn can help calibrate other on-orbit sensors. We will report on the lunar acquisitions and applications planned for the CLARREO Pathfinder mission.

Lunar Radiometric Calibration using Planet Dove Satellites
Arin Jumpasut, Joshua Greenburg, Nicholas Wilson – Planet Labs

ABSTRACT: Captures of the moon at different phases of the cycle, every month are an essential part of Planet's radiometric calibration and validation program [1]. This data has several purposes: initially, an entire moon phase is recorded daily and compared with a radiometric model of the moon (an implementation of the ROLO model [2]) for initial calibration of each satellite. Afterwards, monthly shots at three phase angles in both parts of the moon cycle (waxing and waning) are recorded to capture long term trends and monitor the satellites for inconsistencies. Initial results indicate that the accuracy with regards to the ROLO model is * with an uncertainty of *. This paper describes the experiences and problems that had to be overcome when setting up our fully automated lunar monitoring systems, the initial results using our first flock of 12 satellites at the end of 2016 and our future plans during 2017 when we start to include 88 more satellites into the system.

[1] Jennifer Reiber Kyle, "Radiometric Calibration of the Planet Labs PlanetScope Constellation", Presentation, JACIE 2016

[2] Hugh H. Kieffer and Thomas C. Stone, "The Spectral Irradiance of the Moon", Astronom. J. 129, 2887-2901 (2005)

Extraction of Lunar ROI radiance for the ABI/AHI Lunar Radiance Calibration
Fangfang Yu, Xi Shao – ERT, Inc.; Xiangqian Wu – NOAA/NESDIS/STAR; Masaya Takahashi, Arata Okuyama – Japan Meteorological Agency (JMA)

ABSTRACT: The Moon, due to its extremely stable surface, has been a great interest to the satellite instrument calibration community for instrument in-orbit calibration, sensor-to-sensor inter-calibration, and historical data re-analyses. Yet using the lunar surface as a solar diffuser is always challenged with its non-uniform and non-Lambertian reflectance. To minimize the reflectance variation caused by the phase angle and libration variations, NOAA, in collaboration with Japan Meteorological Agency (JMA), are developing a lunar radiance calibration model over a set of selected region of interest (ROI) which are identified with both lunar hyperspectral and broad-band measurements, and lunar laser altimeter data as well. Yet accurate image-to-image registration to extract accurate ROI radiance is critical for the model development, especially for the images of relatively low spatial resolution bands. Two automatic image registration methods have been developed at NOAA over the past few years – a theoretic method to predict the ROI positions and an empirical algorithm based on the matched local features. Although the theoretic algorithm can well predict the central Moon position, the accuracy of ROI locations is often affected by fluctuations of instrument performance. The current empirical algorithm can successfully achieve the registration accuracy at sub-pixel level for the lunar images within certain phase angle difference, but the registration error increases when the images have large phase angle differences, due to the misclassification of potentially matched features over the global images. In this study, we are proposing to combine the theoretical and empirical methods to increase the number of matched features by restricting the searching area. The resulted lunar ROI radiance will be used to analyze the GOES-16 ABI and Himawari-8 AHI instrument degradations and compared with the solar calibrated data.

10:00 am | 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

Session Chair: Sloane Wiktorowicz, The Aerospace Corporation

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A Cubesat with On-Orbit Calibration System for Radiometric Infrared Imaging
Michael Adkins, Alfonso Amparan, Sandra Collins, John Ferguson, Thomas Kampe, David Osterman, Reuben Rohrschneider, Robert Warden – Ball Aerospace & Technologies Corp.

ABSTRACT: CIRiS (Compact Infrared Radiometer in Space) is a radiometric imaging instrument on a 6U CubeSat bus designed for earth imaging in the thermal infrared (7.5 to 13. 5 um) spectral region. The instrument features a versatile calibration system for optimizing on-orbit radiometric calibration performance, and a modular design facilitating modifications for specialized missions. The objective of the upcoming CIRiS mission is to demonstrate technologies for high calibration performance within 6U CubeSat constraints. These include an uncooled microbolometer imaging focal plane array (FPA) that makes a cryocooler unnecessary, and high-emissivity (e > 0.996) carbon nanotube (CNT) blackbody sources on 1/8 inch-thick solid substrates, the latter replacing bulkier cavity blackbodies.

Instrument on-orbit operation utilizes up to three calibration views to deep space and to two CNT sources, one of which is heated and temperature controlled. A CIRiS radiometric uncertainty budget now under development employs ground measurement and space effect calculations. Thermal drift over the orbit potentially generates radiometric error via the FPA and other instrument components and is therefore the subject of ground measurement. Careful thermal control of the CNT sources and other critical hardware is an integral part of the calibration strategy.

The F/1.8 refractive optical system includes a butcher block filter over the 640 x 480 format FPA. This configuration enables simultaneous imaging in three infrared wavelength bands as the instrument scans the earth from low earth orbit (LEO). Assuming launch from the International Space Station into a 400 km altitude LEO the CIRiS ground sampling distance is 130 m with 83 km swath. On-orbit frame co-adding at the nominal 30 fps frame rate improves imaging and calibration SNR.

CIRiS’ calibration capabilities implemented from CubeSat constellations will enable accurate surface temperature and soil moisture data collection across much of the earth with short, potentially daily, revisit times. Variants on the CIRiS design could also provide an inexpensive and focused complement to more extensive earth radiation imbalance measurements.

Vicarious Radiometric Calibration for Hyperspectral Imaging Microsatellites–SPARK01/02
Hao Zhang, Zhengchao Chen – Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences

ABSTRACT: On 3:22 am December 22 in 2016, two wide-swath hyperspectral imaging microsatellites–SPARK 01/02 manufactured by the Shanghai Engineering Center for Microsatellites, were successfully launched at the Jiuquan satellite launch center by the CZ-2D rocket. Spark01 and 02 has the spectral range of 400-1000 nm, with the spectral resolution ranging from 1-10nm, and their swath is about 100KM with spatial resolution of 50 m. With the characteristics of lightweight, low cost and high performance, the two satellites can also be used in aspects such as environmental and disaster monitoring, target recognition, fine classification, providing basic information support for disaster monitoring, environmental protection, resource development and business application. Due to the lack of satellite calibration equipment, an in-situ vicarious calibration experiment were taken Dunhuang calibration site (500 * 500 m) during February 25 to March 7 in 2017 to derive absolute calibration coefficients for spark01/02. The atmospheric parameters (i.e. aerosol optical depth (AOD) and columnar water content were measured by a sun photometer. The ratio of diffuse irradiance to total irradiance was also measured during a whole day when spark satellite passed. Also, the reflectance of Gobi in the calibration site was measured in two hours before and after the satellite overhead passed. In the meantime, the atmospheric profile was measured by radiosond near the time when satellite passing the calibration site. Modtran5 was used to derive the at-senor radiance based the above in-situ measurements.

At present the absolute radiometric calibration coefficients were derived by the reflectance based method. We analyze the calibration uncertainty through radiative transfer simulation caused by source of uncertainty in aerosol type, AOD, reflectance measurement, etc. The aerosol type assumption would cause much uncertainty in the shortwave bands, with maximum of 10%. The reflectance measurement error is estimated to be 2%, causing calibration uncertainty of 2%. The aerosol optical thickness measurement error of 0.05 wound introduces the calibration uncertainty of 1%. The water vapor measurement error is estimated to be 20%. It imposed much impact on the water vapor absorption bands (near 940 nm), causing a maximum calibration uncertainty of 7%. Besides, calibration uncertainty caused by other resources such as such as the spectral response function changes, observation geometry error, was estimated about 2%. In total, for the non-water absorption bands, the total uncertainty of spark 01 is less than 6%, and that of spark 02 is less than 7%; for the water vapor absorption bands, the uncertainty of spark 01 is less than 8%, and that of spark 02 is within 10%. In the future, we will derive radiometric calibration coefficients of spark 01/02 by irradiance calibration based methods and present more details.

Calibration of a Multi-Spectral CubeSat with LandSat Filters
Sloane Wiktorowicz, Ray Russell, Dee Pack, Eric Herman, George Rossano, David Ardila, Christopher Coffman, Brian Hardy, Bonnie Hattersley – The Aerospace Corporation

ABSTRACT: The AeroCube-11 spectral satellite (also known as AC-11 R3) is a visible and near infrared (VNIR) multispectral pushbroom imager integrated in a 3U CubeSat. AC-11 R3 utilizes six Landsat-8 Operational Land Imager (OLI) filters arranged in a butcher-block configuration overlaid onto the focal plane array (FPA). While CubeSats are designed to be small and relatively inexpensive, thorough ground calibrations were still performed with a short development time. We report on the calibration activities for AC-11 R3, which were performed in one of Aerospace’s TVac chambers fed by a large integrating sphere, a collimator, direct illumination by a lamp, and scattering of lamp light by a Lambertian screen. The calibration tests performed studied dark current (as a function of FPA temperature and gain), reciprocity (by varying illumination and integration time), electron conversion gain (by varying illumination), small source linearity (by toggling a weak source on and off in the presence of a brighter, varying illumination source), flat field, end-to-end spectral response, modulation transfer function (MTF, via a knife edge test), point response function (PRF, via a point source), and distortion (via imaging of a grid of dark points). Some of the lessons learned from the characterization process are recounted to improve speed and efficiency of characterization of similar systems.

A high level GUI was developed to operate the FPA in different modes and to test the effect of low-level FPA settings on data quality. This mitigates human error when manipulating FPA settings at a low programming level. For instance, determination of optimal bias for the FPA for different FPA temperatures and gains is crucial prior to calibration tests. It was necessary to increase bias such that the full +/- 3 sigma distribution of pixel values lay above zero to make accurate statistical assessment of images. Additionally, ensuring optimal clocking of data channels (skew correction) minimizes frame-to-frame variation in signal per pixel. However, as this was performed after the FPA was integrated into the payload, some basic functionality tests were performed on the critical path. Ideally, such testing would be performed prior to FPA integration so experienced users could minimize the time spent on calibration. Finally, rather than performing each calibration test sequentially, we exposed the FPA to a matrix of temperatures, illumination levels, integration times, and gains in order to perform many tests in parallel. For example, the same images may be used for both reciprocity and electron conversion gain.

Slanted Edge MTF Testing for Establishing Focus Alignment at Infinite Conjugate of Space Optical Systems with Gravity Sag Effects
Trent Newswander, Duane Miles, Roy Esplin, Joe Tansock – USU/Space Dynamics Laboratory; David Riesland – Self

ABSTRACT: For space optical systems that image extended scenes such as earth viewing systems, modulation transfer function (MTF) test data is directly applicable to system optical resolution. For many missions it is the most direct metric for establishing the best focus of the instrument. Additionally MTF test products can be combined to predict overall imaging performance. For fixed focus instruments, finding the best focus during ground testing is critical to achieving good imaging performance. The ground testing should account for the full imaging system, operational parameters and operational environment. Testing the full imaging system removes uncertainty caused by breaking configurations and the combination of multiple subassembly test results. For earth viewing, the imaging system needs to be tested at infinite conjugate. Operational environment test conditions should include temperature and vacuum. Optical MTF testing in the presence of operational vibration and gravity release is less straightforward and may not be possible on the ground. Gravity effects are mitigated by testing in multiple orientations. Many space telescope systems are designed and built to have optimum performance in a gravity free environment. These systems can have imaging performance that is dominated by aberration including astigmatism. This presentation discusses how the slanted edge MTF test is applied to determine the best focus of a space optical telescope in ground testing accounting for gravity sag effects. Actual optical system test results and conclusions are presented.

Absolute Radiometric Calibration of the Planet Dove Constellation
Nicholas Wilson, Arin Jumpasut, Joshua Greenburg, Alan Collison, Horst Weichelt – Planet Labs

ABSTRACT: Maintaining the radiometric accuracy of the 140-satellite Planet Dove constellation has required the development of a more automated approach to on-orbit radiometric calibration given the number of satellites and the operational behavior. In nominal operations, Dove Satellites are non-tasking and are nadir pointing. A methodology has been developed that utilizes a hybrid approach to combine lunar calibration and cross calibration to enable on-orbit absolute radiometric calibration of each individual Dove satellite. The cross-calibration approach utilizes instantaneous crossovers in spectrally characterized pseudo-invariant calibration sites with RapidEye, Landsat8, and other Dove satellites. Lunar Calibration utilizes an implementation of the ROLO model [1] and daily moonshots taken by each satellite during both the waxing and waning moon phases. This approach is automated, with new crossovers for each satellite processed and stored daily, and moonshots on a monthly cadence. This has allowed for regular monitoring of the radiometric calibration for each satellite and regular updates to ensure calibration accuracies. Initial validation of this approach using 40 Dove satellites shows an uncertainty of 5% at 1-sigma is achieved across all satellites using instantaneous crossovers with Landsat8 as a validation dataset. This paper describes the absolute radiometric calibration approach, how this method will scale to the larger 140 satellite constellation, and a discussion on the initial results.

[1] Hugh H. Kieffer and Thomas C. Stone, "The Spectral Irradiance of the Moon", Astronomy. J. 129, 2887-2901 (2005)

Self-Assessed Data Quality Standards (SAQS)
B. Guenther, Cole Rossiter – Stellar Solutions, Inc.

ABSTRACT: At the Goddard Memorial Symposium, 2017, Greenbelt, MD, Dr. St. Germain, NOAA NESDIS Lead Engineer, agreed that the evolving systems of Small Satellites may offer significant benefits in terms of cost, schedule, incorporation of technical improvements and risk management for NOAA meteorological applications. But Small Satellite systems do not offer similar benefits for simple incorporation of these data sets for operational forecast models. Many developers of small satellite systems have broad and innovative engineering experience but do not have a broad understanding of what data users expect as background to the data set. [We could consider this information as metadata to the observations data set.] The users consider specific information on how the data is acquired to be essential to understand the details and nuances of the actual data sets. We usually look for detailed information on sensor design, how the sensor was tested, how the test equipment was verified, how the long-term stability of the sensor is established, and how will the data product be validated. Our initial thinking on this matter will be presented, and will be verified with Goddard Ocean Color Biology experience with ingest of the Ocean Color Monitor data from the OCEANSAT-1 Mission.

Additional conversation and discussion on the topic is being carried over to a poster in this Conference. The intent is to provide one potential framework for what users of meteorological data or other data regimes may expect when agencies look to use (purchase?) data from small satellite systems. This information always is easier to organize and provide when developers understand these expectations during the development stage and “bake” their approaches to meeting these expectations into early mission planning. Some institutions that are planning the development of space hardware intended to deliver “data buy” hardware are mature and experienced in these matters and will not need this guidance. Other institutions are not mature and likely do not realize the full expectations of the user community for these metadata.

2:30 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

Session Chair: TBD

View Abstracts (PDF)

Analysis of Systematic Effects in 0/45 Lamp-plaque Sensor Calibration
Eric Shirley, Heather Patrick, Thomas Germer, David Allen, B. Carol Johnson, Howard Yoon – NIST

ABSTRACT: Integrating-sphere sources are convenient for use as near-Lambertian sources to use for calibrating units under test (UUT). An alternative technique is the lamp-plaque method, wherein a calibrated FEL is used to illuminate a polytetrafluoroethylene (PTFE) plaque normally, which in turn is viewed at or 45-degrees off normal by the UUT. This begets several difficulties that should be addressed, including obliquity factors and variable distance of the FEL to points on the plaque, the angular variation of the FEL's intensity, extension of the FEL's calibration as an irradiance standard varying directions and distances, and non-ideality of the Lambertian nature of PTFE. All of these aspects will be discussed.

Planar Detectors as Radiometric Standards using Carbon Nanotube Absorbers at NIST
Nathan Tomlin, Chris Yung, Michelle Stephens, Ivan Ryger, Igor Vayshenker, Solomon Woods, John Lehman – National Institute of Standards and Technology (NIST)

ABSTRACT: Carbon nanotube technology, in conjunction with silicon micro-fabrication techniques, has enabled us to develop planar radiometric detectors, which is leading to the establishment of a new generation of primary standards at NIST. We will discuss the application of this technology to the development of this new generation of chip detectors [1,2]. The goal is to develop compact, fast, and easy-to-use calibration systems, spanning the wavelength spectrum from the ultraviolet to the THz region [3,4] in a single detector, suitable for use with both coherent and incoherent sources, and encompassing open beam and fibre-coupled modes of operation, with utility beyond that of the laboratory environment.

Recent work to enhance the absorptivity of nanotube arrays, using post-growth treatments, and the characterization of noise in temperature sensing thermistors will be presented [5].

Finally, work comparing scales, derived from two new table-top systems, to existing radiant power and optical fibre power scales traceable to SI will be presented.

1. N. A. Tomlin, M. White, I. Vayshenker, S. I. Woods, J. H. Lehman, Planar electrical substitution carbon nanotube cryogenic radiometer, Metrologia 52, 2, 376-383, (2015)

2. N. Tomlin, A. Curtin, M. White, J. Lehman, Decrease in reflectance of vertically-aligned carbon nanotubes after oxygen plasma treatment, Carbon, 74, 329-332, (2014)

3. A. Steiger, R. Mueller, A. Remesal Oliva, Y. Deng, Q. Sun, M.G. White, J.H. Lehman, Terahertz laser power measurement comparison, IEEE Transactions on Terahertz Science and Technology, 6, 5, 664-669, (2016)

4. J. Lehman, A. Steiger, N. Tomlin, M. White, M. Kehrt, I. Ryger, M. Stephens, C. Monte, I. Mueller, J. Hollandt, M. Dowell, Planar hyper-black absolute radiometer, Optics Express, 24, 23, 25911-25921, (2016)

5. I. Ryger, D. Harber, M. Stephens, M. White, N. Tomlin, M. Spidell, J. Lehman, Noise characteristics of thermistors: Measurement methods and results of selected devices, Review of Scientific Instruments, 88, 2, 024707, (2017)

Traceable Radiometric Calibration of the German Imaging Spectrometer Satellite Mission EnMAP
Andreas Baumgartner – German Aerospace Center (DLR)

ABSTRACT: The Remote Sensing Technology Institute (IMF) of the German Aerospace Center (DLR) operates a laboratory for the radiometric, spectral and geometric calibration of imaging spectrometers. Though, mainly used for the calibration of airborne sensors the laboratory is additionally used for the development and test of calibration techniques for the German satellite mission EnMAP.

For the calibration of spectrometers in the spectral range from 380 to 2500 nm the self-monitoring radiance standard RASTA was developed which is calibrated by the National Metrology Institute of Germany (PTB).

RASTA will be used as the radiometric standard for the laboratory calibration of EnMAP. Due to the limited size of the RASTA’s radiance field, EnMAP cannot be directly calibrated with it. Therefore, the calibration is transferred to an integrating sphere using a spectrometer.

The non-uniformity of the integrating sphere’s light field is determined with high spatial and spectral resolution by an approach developed by DLR. To minimized errors introduced by the non-uniformity of the integrating sphere, a setup was developed which allows the determination of the spot actually measured with the spectrometer. This will guarantee that EnMAP measures the same spot of the sphere which is calibrated with the spectrometer

Preliminary Results of Solar Diffuser BRDF Measurements using a Table-top Goniometer at GSFC NASA
Jinan Zeng – Fibertek Inc.; James Butler, Jack Xiong – NASA Goddard Space Flight Center; Leibo Ding – Science Systems and Applications, Inc. (SSAI)

ABSTRACT: We report the development of a table-top goniometer at GSFC, NASA, and the preliminary results of solar diffuser BRDF measurements for satellite instrumentation in the reflective solar bands. The table-top goniometer is able to conduct both in-plane and out-of-plane BRDF measurements, which was built up using commercial stages and opto-mechanics to minimize the need for extensive machining. Various light sources with the power stabilities of < 0.5 % cover the 300 nm to 2500 nm wavelength region. These include a laser diode driven plasma broadband light source, such as a Xe lamp, a supercontinuum laser, and single wavelength lasers. The broadband sources can be used either with dispersive elements to generate monochromatic light, or as built. Si and extended InGaAs detectors cover the spectral range from 300 nm to 2500 nm and are used in absolute and relative BRDF measurements. Two mini-spectrometers operating in the UV-NIR and NIR-SWIR measure the spectra of scattered light from the broadband sources in a measurement of relative BRDF. Two NIST traceable Spectralon standard samples, a white diffuser and black diffuser, are used to validate the system and to make comparison measurements. We present the spectral coverage of light sources and their stabilities, the detector linearities, and signal to noise ratios. The BRDF results at specific wavelengths are also shown in the different configurations to verify the BRDF reciprocity of diffuser at the angles of interest. We also present the methodology of how to complete the BRDF measurements beyond the spectral and angular coverage of NIST traceable standards. The uncertainty budget of BRDF measurements will also be discussed.

4:30 pm | SPOTLIGHT Session Sentinel

Session Chair: TBD

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Results from the Radiometric Absolute Calibration of Sentinel-2A and Sentinel-2B
Charlotte Revel, Arthur Dick, Vincent Lonjou, Sebasien Marcq, Thierry Tremas – Centre National d'Etudes Spatiales (CNES)

ABSTRACT: The Sentinel-2A and Sentinel-2B were respectively launched in June 2015 and March 2017. The SENTINEL mission is dedicated to Earth’s land surfaces in order to monitor vegetation and land cover evolution. The SENTINEL constellation provides images to various spatial resolutions (from 10m to 60 depending on the band) for the 13 spectral bands (from 443 to 2190nm) with a high revisit frequency (5 days for both Sentinel- 2A and 2B). The instruments are in-flight calibrated and characterized primarily using on-board device (diffuser). Vicarious calibration methods are used in addition to validate the on-board calibration. Various natural sites and phenomenon are used such as Rayleigh scattering for absolute calibration in the short wavelengths range, desert for cross-satellite calibration and Deep Convective Clouds (DCC) for cross-band calibration. Based on these methods, it is also possible to provide an accurate checking of many radiometric aspects and on a large range of scenes. The vicarious calibration also allows to check the cross calibration between Sentinel-2A and 2B and also between many other instruments such as MERIS or MODIS. The results of the Sentinel-2A and Sentinel-2B calibration obtained with the on-board device will be briefly presented. Afterwards, we will focus on calibration results from vicarious methods which will be presented and discussed.

System Vicarious Calibration of Sentinel-3 OLCI
Nicolas Lamquin, Ludovic Bourg, Christophe Lerebourg, François-Régis Martin-Lauzer – ACRI-ST; Ewa Kwiatkowska – European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT); Steffen Dransfeld – European Space Agency (ESA)

ABSTRACT: Sentinel-3A (S3A), carrying the Ocean and Land Colour Instrument (OLCI), was successfully launched on February 16th 2016. It was the first of the series planned by the European Commission (EC) in the frame of COPERNICUS Sentinel program. Sentinel-3B is planned for launch in late 2017, bearing identical instruments, thus improving the global Earth coverage. The OLCI series providing global coverage at 300m resolution will therefore represent a major breakthrough in the family of ocean colour sensors.

For being an operational mission feeding in downstream Copernicus services like CMEMS, it is essential to ensure product quality prior public release. As for most ocean color missions, this supposes the implementation of a system vicarious calibration (SVC). Based on the methodologies applied to MERIS (and historically to older sensors), SVC of OLCI is performed separately for near-infrared (NIR) and visible (VIS) bands.

NIR bands SVC is performed over dedicated oligotrophic targets. Over such waters the marine signal is negligible in this spectral region compared to the contribution of the atmosphere. This avoids the use of in situ colocated data and provides enough sensor observations for the analysis and the computation of vicarious calibration gains. Different methodologies are tested and their intercomparison provides the conclusion that a simple unweighted regression on the NIR aerosol reflectances provides robust consistency in the obtained gains.

On the other hand, VIS bands SVC relies on OLCI observations matching very high quality in situ measurements after calibration of the NIR. For the time being, only two operational stations provide sufficiently high quality data for this purpose: BOUSSOLE in the Mediterranean Sea and MOBY in the Pacific Ocean. The number of accurate vicarious calibration matchups to ensure statistically reliable gains is discussed. To increase the statistics and improve reliability, an alternative procedure based on the use of global daily climatologies is shown to provide consistent additional measurements for the computation of robust SVC gains in the VIS.

In this presentation, the implemented SVC procedures for OLCI are described along with the analysis ensuring their reliability. OLCI product quality improvement brought by SVC is shown through the analysis of individual user products as well as by comparison with in situ data and other sensors.

Alternative Gain Estimates for OLCI: Atmosphere-typed Spectral Optical Thickness Corrections for the Vicarious Calibration
Bertrand Saulquin, François-Régis Martin-Lauzer – ACRI-ST

ABSTRACT: Vicarious calibration aims at fitting TOA observations to estimates. The historical formulation of the gain G*ρ_TOA= ρ_path+T*ρ_w allows centering the model with the observations. Nevertheless, this formulation doesn’t allow discretising errors made either in the transmittance T or in the atmosphere reflectance ρ_path,. i.e. identifying the error sources.

We propose here a vicarious calibration, both in shape and amplitude, of the estimated spectral optical thicknesses. We show that, in open ocean waters, using the GlobColor dataset complemented by data collected by MOBY, that the direct model used to calculate ρ_TOA underestimates the total optical thicknesses for some 2% at 400nm to 0.02% at 681nm. The new formulation of the vicarious adjustment involves a non-linear correction which adjusts in a better way than the historical formulation both the atmospheric components (ρ_path, T) and the water reflectances ρ_w.

Discrepancies are also assessed in coastal areas, and it is possible to correct them using a vicarious calibration scheme which involves probability-based transitions between clear maritime and continental aerosol-loaded coastal atmospheres. By introducing continuous transitions between multiple modes, we maximize the fitness of ρ_w in the two cases. It may initiate the use of conditional gains for the current level 2 processors of optical EOs.

An example will be shown for OLCI, with the provision of gains values, including their uncertainty estimates, and the improvement of ρ_w in absolute and relative terms.

Alternative vicarious calibration for OLCI, MODIS, VIIRS; Spectral optical thickness corrections; Atmosphere-typed mixture of gains

This research is a follow-up of the work for the E.U. Copernicus Marine Service Information , and the Sentinel-3 Mission Performance Centre

Sentinel-3A – In-flight Radiometric Calibration of OLCI&SLSTR Sensors Based on Natural Targets
Bertrand Fougnie, Camille Desjardins, Bruno Besson, Christine Miquel, Nicolas Guilleminot – Centre National d'Etudes Spatiales (CNES); Véronique Bruniquel, Naceur Meskini – ACRI-ST

ABSTRACT: The main objective of the SENTINEL-3 mission is to measure sea surface topography, sea and land surface temperature, and ocean and land surface colour with high accuracy and reliability to support ocean forecasting systems, environmental monitoring and climate monitoring. The mission provides data continuity for the ERS, Envisat and SPOT satellites. The first SENTINEL-3 mission, launched in February 2016, is jointly operated by ESA and EUMETSAT to deliver operational ocean and land observation services. Sentinel-3 is making use of multiple sensing instruments to accomplish its objectives. Two of them, OLCI (Ocean and Land Colour Instrument) and SLSTR (Sea and Land Surface Temperature Radiometer), are optical sensors designed to provide a continuity with Envisat's instruments and are follow-on of MERIS and AATSR instruments.

OLCI is based on the design of the MERIS instrument, i.e. a push-broom imaging spectrometer with a total swath width of 1270 km, a spatial sampling acquisition of 300m for 21 spectral bands from 0.4 to 1.02 microns. SLSTR is based on the design of AATSR instrument, i.e. a conical scanning imaging radiometer with a total swath of 1420km nadir, a spatial sampling of 500m (VIS-SWIR) and 1000m (MWIR, TIR) for 9 spectral bands from 0.55 to 12 microns. Both instruments have on-board devices in order to build and monitor the in-flight calibration.

We present here the results of the vicarious calibration methods used to estimate OLCI and SLSTR in-flight calibration. These methods are statistical, based on natural targets, and already successfully tested on many sensors (MODIS, MERIS, POLDER, S2…). Calibration over PICS (desert and Antarctica sites); oceanic sites (Rayleigh scattering and sunglint) and cloudy sites (DCC) were all operated. Moreover, the combination of all methods provides a powerful validation of the in-flight recalibration, but also allows observing very small signatures, as for instance the early OLCI ageing observed by the on-board diffuser. After more than 1 year in orbit, absolute, interband, multi-angular, temporal calibration as well as cross-calibration with many sensors will be presented for both instruments.

Thursday, August 24, 2017

8:00 am | Advancements in Radiometric Calibration State-of-the-Art

Techniques, equipment, methods, and processes to advance the productivity and value of radiometric calibration

  • Techniques and technologies to meet calibration performance requirements for advanced programs
  • Methods and techniques for efficient processing of large volumes of remote sensing data
  • Real-time calibration data analysis and performance assessment
  • Translation of program science requirements into radiometric calibration requirements
  • Efficient experiment data collection design to reduce radiometric calibration schedule and cost
  • Practices to establish and maintain traceability to accepted National standards throughout program life

Session Chair: Bruce Guenther, Stellar Solutions

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Validation of NIST’s Low Temperature Infrared Spectral Radiance Scale
Sergey Mekhontsev – National Institute of Standards and Technology (NIST)

ABSTRACT: We have performed measurements of a high emissivity fluid bath variable temperature blackbody source against our reference ammonia heat pipe blackbody from -45 °C to 25 °C. Although the two blackbodies are of very different designs, the spectral radiance results are consistent with calculations based on reference thermometer measurements and effective emissivity data.

Both blackbodies employ liquid coolant (ethanol) and two stage refrigeration: internal to the fluid bath LTBB and via an external recirculating bath for the AHPBB. In the case of the AHPBB, the coolant cools the ammonia heat pipe, which provides uniform temperature to the cavity, which it surrounds. The cavity of the LTBB is directly immersed in a bath, which also contains cooling coils for the refrigerant. Temperature uniformity is achieved by stirring the coolant. The radiating cavities are also of different designs. The AHPBB has a typical deep cylinder cavity with a shallow rear cone and is coated with a diffuse black paint, while the LTBB cavity is a trap design with a shorter cylinder section and a longer steeper cone, coated with a specular black paint. In each case, using coating data and cavity modeling, the effective emissivity was calculated to be ≥ 0.9999 from 3.5 µm to 14 µm.

We used the Infrared Spectral Emittance Facility (ISEF) to perform a comparison of the two blackbodies across the spectral and temperature ranges previously described. The radiance temperature and effective emissivity results were found to be within the expanded uncertainty of the measurement process, providing validation of the scale.

Next Generation Calibration Sources for European Mission of Earth Observation
Mathieu Maisonneuve, Robert Bouchard, Jacques Giroux – ABB Canada

ABSTRACT: ABB is currently involved in several European projects for earth observation, namely MTG-FCI, MTG-IRS, IASI-NG and METimage, supplying high end calibration sources for MWIR and LWIR bands. Calibration sources are critical sub-systems providing reliable and traceable data for meteorological forecasting as well as long-term climate monitoring.

This presentation will focus on the proposed blackbody design and test campaign. An overview of the design based on ABB developed technology will be done given. Advantages of this technology will be listed and compared to the need of the targeted mission. Planned and actual performance parameters of the different blackbody will be presented and compared to their requirements. The repeatability of radiometric performances from one unit to another will also be discussed. Some specific test results of MTG-FCI blackbody test campaign will be presented with a highlight on the radiometric measurements that were done using the radiometric setup presented last year.

Feasibility Demonstration of Near-surface Unmanned Aircraft Systems for GOES-R ABI Validation
Aaron Pearlman, Francis Padula – GeoThinkTank LLC; Tung-Chang Liu, Xi Shao – University of Maryland; Changyong Cao – NOAA/NESDIS/STAR; Steven Goodman – NOAA/NESDIS/GOES-R Program Office

ABSTRACT: The Geostationary Operational Environmental Satellite R-Series (GOES-R) field campaign was focused to provide validation of the SI traceability of the Advanced Baseline Imager (ABI) established pre-launch. In support of this objective, an advanced capability development effort was initiated, “GOES-R near surface unmanned aircraft system (UAS) feasibility demonstration study” to meet the long-term challenges of validating next generation sensors. We report on the results of this 18-month study to design and develop the prototype systems, both rotary and fixed wing. The rotary UAS is the primary system focused on radiometric validation consisting of a sensor suite with hyperspectral (reflective solar) and broadband thermal infrared measurement capabilities, in addition to a high-resolution context imager. We will discuss the design, characterization, and integration stages of development, as well as functional and operation environment flight testing. The rotary system design takes advantage of off-the-shelf technologies and fiber-based optical components to simplify integration and commanding. The characterization results - including laboratory measurements of temperature effects and polarization sensitivity - are used to refine the radiometric uncertainty budget towards meeting ABI validation objectives. The functional performance and operational environment tests demonstrated autonomous/semi-autonomous UAS validation flights with stabilized gimbal pointing and geo-referenced data product generation from all sensors. The system and testing refinements throughout the development with respect to calibration procedures, fiber configurations, command and data handling, and electrical connection hardening will be reviewed to highlight the lessons learned in this effort and inform the path forward towards maturing this capability for operational use. Such systems have the potential to create a rapidly-deployable, affordable, flexible validation capability that builds off the heritage approaches and can meet the unique challenges of GOES-R ABI and other next generation satellite systems.

Vicarious Calibration of the RapidEye Constellation using the RadCalNet Automated Calibration Sites
Andreas Brunn, Sara Bahloul, Dietrich Hoffmann, Horst Weichelt – Planet

ABSTRACT: RapidEye is a commercial constellation of five satellites, each carrying a 5-band multispectral pushbroom imager. The band combination, including the first commercially available Red-Edge band on a multispectral satellite, makes the constellation ideal for land-use and land-cover applications.

Vicarious calibration methods are used to ensure the accurate and consistent calibration of the imagers required by these applications. Previously, the absolute calibration was performed based on labor intensive ground measurement campaigns. This talk presents the results of the use of the automated calibration sites maintained within the RadCalNet network. Specifically, the results using data from the La Crau and Railroad Valley sites are shown, together with a validation of the processing of ground reflectance to top-of-atmosphere reflectance.

Elimination of Artificial Bright Pixels in Visible Infrared Imaging Radiometer Suite Day/Night Band Nighttime Image over the South Atlantic Anomaly Region
Yalong Gu, Slawomir Blonski, Wenhui Wang – Earth Resources Technology, Inc.; Sirish Uprety – Cooperative Institute for Research in the Atmosphere, Colorado State University; Changyong Cao – Center for Satellite Applications and Research, NOAA/NESDIS

ABSTRACT: The Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) is a panchromatic visible and near-infrared band capable of quantitative measurement of light radiances from 3×10-9 W∙cm-2∙sr-1 to 2×10-2 W∙cm-2∙sr-1. Its extreme sensitivity of the HGS to low lights, together with the nearly constant spatial resolution over the whole swath, enables numerous applications of environmental remote sensing and global monitoring of anthropogenic activities in nighttime. However, the DNB is susceptible to high energy particles (HEPs) hitting over the South Atlantic Anomaly (SAA) region. Although a special algorithm was designed to filter out high radiance pixels induced by HEPs, large amount of artificial bright pixels are still observed in the generated DNB nighttime images, leaving obstacles for several image based applications, such as automatic fishing boat detection over the SAA region.

In this study, we investigated DNB nighttime images over the SAA region. It has been shown that the DNB gain selection logic is the possible root cause for the isolated bright pixels in DNB nighttime images over the SAA region. This result was confirmed by a recent DNB special data acquisition over the SAA region. With the knowledge acquired from the analysis of root cause, we explored method to eliminate artificial bright pixels induced by the HEPs over the SAA region. Our method could improve the DNB nighttime image quality over the SAA region and potentially benefits monitoring of anthropogenic activities in nighttime over that region.

2:00 pm | Spotlight Session: Recent Advances in On-orbit Radiometric Calibration

Session Chair: Dennis Helder, South Dakota State University

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A Comparison of Relative Gain Estimation Methods for High Radiometric Resolution Pushbroom Sensors
Dennis Helder, Cody Anderson, Drake Jeno – South Dakota State University

ABSTRACT: Modern optical remote sensing satellite instruments are increasingly using a pushbroom design for the focal plane and are also incorporating greater radiometric resolution with 12 bits/pixel, or greater, becoming more common. Both of these design features demand that high precision methods be developed for estimating the relative gain differences among detectors on the focal plane. This paper reviews three approaches – onboard diffuser, side-slither, and lifetime statistics – and provides a direct comparison of their performance. All three methods of relative gain estimation, onboard diffuser, side slither, and lifetime statistics, are capable of excellent performance and can be used for high radiometric resolution optical sensors. For those sensors that have the luxury of an onboard diffuser, a diffuser-based approach can provide accurate relative gain estimates as often as needed by the sensor. Conversely, for those systems that cannot accommodate a diffuser panel, both the side slither and lifetime statistic methods work well. For those sensors that cannot perform a yaw maneuver, the lifetime statistics approach provides adequate results. Thus, a methods for estimation of relative gains is always available for any type of sensor capability.

On-orbit Optical Sensor Bias Estimation
Cody Anderson – Stinger Ghaffarian Technologies; Nischal Mishra – System Sciences and Applications Inc. (SSAI)

ABSTRACT: As focal planes become larger and more pixels are added, understanding each individual sensing element becomes more difficult. This paper will focus on one fundamental characteristic of every electronic sensing element: bias and its estimation. Bias estimation and removal is a necessary process for connecting the electronic signal received from a remote sensing optical sensor to a useful scientific physical unit. Although a simple calculation in the end, the bias behavior for each individual sensor and each individual sensing element must be understood. Several different special calibration image collects can give an instantaneous measurement of bias, and the frequency of these collects can track the behavior over time. This paper will discuss the type and frequency of special calibration collects needed for input into the simple bias estimation calculation.

Index Terms— bias, offset, dark, estimation, calibration, radiometry, optical, Landsat

Assessing Long Term Stability of LANDSAT 5 TM, LANDSAT 7 ETM+ and LANDSAT 8 OLI
Esad Micijevic, Md. Obaidul Haque – Stinger Ghaffarian Technologies (SGT Inc.); Nischal Mishra – System Sciences and Applications Inc. (SSAI); Dennis Helder – South Dakota State University

ABSTRACT: The radiometric calibration stability of Landsat 5 (L5) Thematic Mapper (TM), Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 (L8) Operation Land Imager (OLI) is continuously monitored, trended, and updated using various on-board and vicarious calibration techniques. The on-board calibrators in L5 TM and L7 ETM+ were deemed unreliable after a few years of on orbit operations, therefore methods based on analysis of Pseudo Invariant Calibration Site (PICS) responses have been used to assess and update the temporal gain changes of these instruments. Long term trending from PICS, primarily located in the Saharan region, indicate that long term degradations are less than 0.05% per year in L7 ETM+ bands and less than 0.2% per year in L5 TM bands. On the other hand, L8 OLI has well behaved on-board calibrators that are used to assess the stability of the instrument while PICS are used as a complementary method. Statistics derived from these on-board calibrators indicate that all bands in OLI are stable to within 0.05% per year, except the Coastal Aerosol Band where all on-board calibrators indicated a systematic degradation of about 0.2% per year. Recently, the US Geological Survey (USGS) Earth Resources Observation and Science (EROS) addressed this degradation within the Landsat Collection 1 product generation. PICS statistics from L8 OLI indicated trends that differ from the on-board calibrator trends by about 0.35%. Further analyses of L7 ETM+ trends show that due to PICS variability more than four years’ worth of PICS data are needed to better estimate the long term stability of the Landsat sensors.

Improved Temporal Resolution of Peduto Invariant Calibration Sites (PICS) Through Development of the PICS Normalization Process
Morakot Kaewmanee, Harika Vuppula, Dennis Helder – South Dakota State University

ABSTRACT: PICS (Pseudo Invariant Calibration Sites) have been used for on-orbit radiometric trending of optical satellite sensors for many years. It takes advantage of the properties of PICS which is highly invariant, any trend in the data would indicate a change in sensor responsivity rather than a change in the apparent reflectance of the target/atmosphere system. However, the length of time that is required to determine a change in sensor responsivity is measured by the drift estimates using a function of the residual noise in the PICS target/atmosphere system and the number of days between imaging opportunities with the sensor being calibrated. Often this can require several years of imaging PICS, using only cloud free data, to detect a small change in sensor responsivity. Six primary Saharan PICS locations were selected according to their level of temporal/spatial stability. Each of these sites was normalized to the well-known Libya- 4 PICS which is used as the overall reference calibration site. Pseudo Invariant Calibration sites (PICS) Normalization process (PNP) is a technique developed to combine sensor observations of multiple PICS into a single time series with greater temporal resolution for satellite calibration. As a result, the temporal resolution using this method can theoretically be improved by a factor of four. This PNP technique was applied to Landsat-8 data to determine if small changes in sensor responsivity can be detected in a shorter time period than when only one PICS is utilized in the trending process. It was found that the PNP, using almost 4 years of image observations over 6 primary PICS, can give a sensor trending estimates to within 0.50 % per year for all VNIR and SWIR bands.

Index Terms— PICS, PNP, calibration, trending, Landsat-8

Landsat 8 OLI and TIRS Calibration Updates and Trends for the Period of 4 Year of Operation
Raviv Levy, Julia Barsi – Science Systems and Applications Inc. (SSAI); Brian Markham – NASA Goddard Space Flight Center

ABSTRACT: Landsat 8 had been in orbit and operational for more than 4 years which brings it to the milestone of passing 80% of the official design lifetime for its Operational Land Imager (OLI) payload and past the full lifetime for the Thermal Infrared Sensor (TIRS) payload. This paper will report about the status of the operational payloads, highlighting trends and stability of the absolute and relative radiometric response. It will also describe the status of other core performance parameters such as SNR, NEdT, uniformity, highlighting how calibration updates made in the USGS data processing system to maintain and enhance the quality of the data helped in reducing uncertainties, overcoming hardware anomalies. For OLI we will present the trends for its on-board calibration components and for TIRS we will demonstrate how application of stray light correction implemented since the new Collection 1 release can assist in tightening the TIRS band 10 radiometric products accuracy.

4:20 pm | 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

Session Chair: TBD

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Radiometric Calibration Network for Vicarious Calibration of Earth Observing Imagers in the Reflected Solar
Kurtis Thome – NASA Goddard Space Flight Center; Jeff Czapla-Myers – University of Arizona; Marc Bouvet, Philippe Goryl – European Space Agency (ESA); Béatrice Berthelot – Magellium; Nigel Fox, Emma Woolliams – National Physical Laboratory (NPL); Patrice Henry, Aimé Meygret – Centre National d'Etudes Spatiales (CNES); Chuanrong Li, Lingling Ma, Lingli Tang – Academy of Opto-Electronics; Brian Wenny – Science Systems & Applications, Inc. (SSAI)

ABSTRACT: A challenge for the scientific community in respect to the ever-increasing number of Earth observing satellite sensors is to ensure that the absolute radiometric calibration of the sensors is harmonized to the same SI-traceable scale. Assessing the post-launch radiometric calibration is the responsibility of each sensor team and typically involves simulating the top-of-atmosphere signal from in-situ and atmospheric measurements. As this is done on an individual sensor-by-sensor basis often using a single ground site, radiometric biases can exist between sensors. In an effort to minimize these biases, the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) Infrared Visible Optical Sensors (IVOS) is currently working to develop the prototype radiometric calibration network, RadCalNet. This network will standardize methodology and processing streams for participating ground sites. The current RadCalNet working group consists of members from the National Aeronautics and Space Administration (NASA, USA), the Centre National d’Etudes Spatiales (CNES, France), the European Space Agency (ESA), the National Physical Laboratory (NPL, UK), the University of Arizona (USA), and the Academy of Opto Electronics (AOE, China). Four radiometric calibration test sites in the USA, France, China, and Namibia are being used as test cases for the collection of surface reflectance and atmospheric data, which are then converted to top-of-atmosphere (TOA) reflectance for comparison with a limited number of satellite sensors. The goal of the RadCalNet working group is to provide via a public website site the hyper-spectral (in the range 400 nm to 1000 nm and at specific sites up to 2500 nm) top-of-atmosphere reflectance at 30-minute intervals for a nadir viewing sensor for the 4 sites. RadCalNet recently completed its Beta Testing Phase and examples from that testing phase as well as a description of the method for providing uncertainties and ensuring SI-traceability are presented.

New RadCalNet Instrumented Site at Gobabeb, Namibia: Installation Field Campaign and First Absolute Calibration Results
Sebastien Marcq, Aimé Meygret – Centre National d'Etudes Spatiales (CNES); Agnieszka Bialek, Claire Greenwell, Nigel Fox – National Physical Laboratory (NPL); Marc Bouvet – European Space Agency (ESA); Beatrice Berthelot – Magellium

ABSTRACT: A new permanently instrumented radiometric calibration site for high/medium resolution imaging satellite sensors in the visible/near-IR has been set up in Namibia, near the Gobabeb Research and Training Centre on the edge of the Namib Desert. This site is the European contribution to the Committee on Earth Observation Satellites (CEOS) initiative RadCalNet (Radiometric Calibration Network). The Gobabeb area has been selected based on the analysis of different datasets to estimate surface spatial homogeneity, cloud coverage, temporal variability, atmospheric turbidity and flatness.

A field campaign took place in November 2015 in order to find the precise location of the future permanent instrumentation in the area identified from satellite data (Modis, Landsat8, Sentinel2, Pleiades). This location is the one with the best spatial homogeneity at different scales: instrument field-of-view (tens of centimeters), extent of the instrument-monitored area (tens of meters) and satellite sensor resolution (tens to hundreds of meters). The field campaign also focused on the characterization of the surface reflectance, the surface hemispherical directional reflectance factor and the atmospheric turbidity.

Following this campaign, the permanent instrumentation (CIMEL photometer) has been installed in June 2017 and has the ability to measure atmosphere (aerosol optical thickness etc.) and surface conditions (reflectance). The data has been processed by the ROSAS processing software at CNES in order to obtain first results of surface reflectance and to perform the vicarious absolute calibration of optical sensors (Sentinel2A and Sentinel2B, Landsat8 etc.)

The presentation will focus on the installation field campaign and the analysis of the data produced by this new calibration station.

Consistent Pre-2000 GEO Visible Calibration Record Based on Deep Convective Clouds and Desert Targets
Rajendra Bhatt, Arun Gopalan, Conor Haney, Benjamin Scarino – Science Systems and Applications, Inc. (SSAI)

ABSTRACT: The ISCCP project provides a 40-year geostationary (GEO) imager record of 3-hourly cloud properties and surface reflectances. ISCCP coordinated the ingestion of 3-hourly geostationary imager pixel level radiances, placing them in a common format across GEO imagers and archiving the datasets for future reprocessing efforts. The ISCCP project is currently is trying to faithfully reproduce the historical DX results in the new processing environment. Once this has been achieved, new calibration coefficients and cloud retrieval algorithms can be processed and compared to the original algorithms and validated for stability across the record.

CERES is currently releasing their Edition4 data products, where the GEO imager calibration, has been referenced to the Aqua-MODIS band 1 Collection 6 calibration ( The same calibration approach was applied to the 40-year AVHRR visible imagers record ( The pre-2000 GEO imager calibration strategy relies on deep convective cloud and invariant desert calibration targets, which have been characterized using post-2000 reference GEO imagers based on the Edition 4 calibration. Since the GEO imaging schedules do not change over time, the angular distribution of the targets repeat themselves annually. This approach will provide better stability across sensors, rather than using ray-matched AVHRR/GEO radiance pairs, since the NOAA satellite orbits drift in time, making it difficult discern GEO calibration and NOAA satellite drifts. This provides the ISCCP project another set of calibration coefficients, which are consistent across sensor platforms, in order to retrieve climate quality cloud properties.

Satellite Intercalibration and Validation using the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley, Nevada
Jeff Czapla-Myers, Nikolaus Anderson, Stuart Biggar – University of Arizona

ABSTRACT: The Radiometric Calibration Test Site (RadCaTS) is an automated facility developed and operated by the Remote Sensing Group at the College of Optical Sciences at the University of Arizona. It is located at Railroad Valley, Nevada, USA, and has been in operation in its current form since 2012. RadCaTS was originally developed in the mid-2000s in response to the ever increasing number of Earth observation sensors on orbit, and it includes instruments used to make surface reflectance and atmospheric measurements in order to determine the top-of-atmosphere quantities (e.g. spectral radiance and reflectance). In addition, the surface reflectance at Railroad Valley can be used to validate surface reflectance algorithms. The primary motivation for RadCaTS is the ability to make near-continuous measurements throughout the day during clear-sky conditions while retaining a level of uncertainty on par with the more traditional reflectance-based approach to vicarious calibration. RadCaTS is also one of the four instrumented sites that make up the CEOS WGCV Radiometric Calibration Network (RadCalNet), which seeks to coordinate the efforts of space agencies to harmonize the SI traceability of satellite sensors. RadCaTS calibration and validation results for various Earth-observing sensors are presented for the period 2012–2017.

Friday, August 25, 2017