Monday, August 30, 2021
11:00 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.
Session Chair: Arin Jumpasut, Planet
Characterization for IR and Microwave Instruments with Solar System Objects
Martin Burgdorf, Stefan Buehler – Universität Hamburg; Viju John – European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)
ABSTRACT: Serendipitous observations of our Moon or planets of the inner solar system provide a unique means to the characterization of the (quasi-)optical properties of instruments on meteorological research satellites in flight, because their diameters are much smaller than the size of a pixel or the field of view. We investigated how beamwidth, channel co-registration, and pointing accuracy can be determined with such observations. For this we identified and analysed intrusions of the Moon in the deep space views of AMSU-B (Advanced Microwave Sounding Unit - B) and MHS (Microwave Humidity Sounder) on various satellites in polar orbits and as well images obtained with SEVIRI (Spinning Enhanced Visible Infra-Red Imager) on Meteosat-10 and -11, which had Mercury or Venus standing close to the Earth in the rectangular field of view.
When the Moon moves by chance through the field of view of a microwave sounder, it is possible to calculate the beamwidth and pointing direction of each channel. We found significant discrepancies between the results of these measurements in flight and those obtained during ground tests with both AMSU-B and MHS on certain satellites. In several of these cases we detected non-compliance with requirements that had not been recorded in test reports.
Studies of the channel alignment and image quality are presented as well for SEVIRI. As the angular resolution of this instrument is about a hundred times higher than with microwave sounders, we replaced here the Moon with Mercury and Venus. We characterized the typical smearing of the planet’s radiance into neighbouring pixels with infrared channels and occasionally we detected large shifts of the scan lines in the raw data that tear a planet’s image apart by dozens of pixels. Once these misalignments between scan lines are corrected, however, the band-to-band registration is accurate within a small fraction of a pixel, even for detectors on different focal planes.
ARCSTONE: Calibration of Lunar Spectral Reflectance from Space
Constantine Lukashin, Trevor Jackson, Jacob Benheim, Michael Cooney, Warren Davis, Thuan Nguyen, Noah Ryan, Rodolfo Ledesma, Cindy Young – NASA Langley Research Center; Greg Kopp, Seth Cousin, Paul Smith – Laboratory for Atmospheric and Space Physics (LASP), University of Colorado; Rand Swanson, Hans Courrier, Michael Kehoe, Michael Stebbins – Resonon, Inc.; Christine Buleri – Quartus Engineering, Inc.; John Carvo, Jacob Payne – Blue Canyon Technologies, Inc.; Thomas Stone – U.S. Geological Survey
ABSTRACT: Detecting and improving the scientific understanding of global trends in complex Earth systems, such as climate, increasingly depend 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, however, 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 utilized as an on-orbit calibration target by most space-borne 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 spanning the visible and near-infrared spectral regions. The ARCSTONE instrument is a compact spectrometer which will be packaged on a 6U 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 referenced to the spectral solar irradiance across the 350 to 2300 nm spectral range. This lunar reference will help to enable high-accuracy absolute calibrations and inter-calibrations of past, current, and future Earth-observing sensors, meteorological imagers, and long-term climate monitoring satellite systems. The ARCSTONE team will present the development status of the instrument, results from laboratory characterizations and functional tests, and the planned path toward mission implementation.
Advances in the SLIM Lunar Spectral Irradiance Model; Many Observations, One Moon
Hugh Kieffer – Celestial Reasonings
ABSTRACT: Work on the Spacecraft and Earth-based Lunar Irradiance Model (SLIM) system has concentrated on the SLIMED model (pronounced as if you lost weight), which uses a weighted least-squares fit to many instrument data sets and is continuous in all dimensions. Total Solar Irradiance (TSI) and Solar Spectral Irradiance (SSI) variations are now included. A libration correction to the observations based on integration of reflectance maps made by Lunar orbiters can be included. Current fits involve 2 observatory sets (ROLO and NIST:Cramer) and 8 LEO instruments (SeaWiFS, L8-OLI, Hyperion, Terra and Aqua MODIS, SNPP-VIIRS, PLEIADES A and B) for a total of 99,000 points with mean-absolute-residual of 0.6% . Data from GEO instruments thus far show too much variation in irradiance to be included in the fits.
All the above instruments, plus GOES-8,9,10,11,12,14,15, SEVIRI 1 to 4, GOES-16 and 17 ABI (and NOAA20-VIIRS) have been calibrated with a SLIMED model and the average gain bias of each instrument band derived, as well as asymptotic trends and in some cases periodic variations. There is general agreement at the few percent level for some operational instruments yet significant differences between others. The magnitude of differences between instruments suggests that the methodology of extracting lunar irradiance from lunar images is the culprit in many cases. As lunar models improve, more detailed image-processing will be warranted. Understanding the hardware and processing differences between nadir and lunar imaging can require special sequences, preferably planned during commissioning.
There is still a lot of work to be done to approach the potential utility of lunar calibration, ppt or better! All spacecraft teams with lunar observations are invited to participate.
Airborne LUnar Spectral Irradiance (Air-LUSI) Mission: Steps to High Accuracy
John Woodward, Steven Brown, Stephen Maxwell, Steve Grantham, Thomas Larason – National Institute of Standards and Technology (NIST); Kevin Turpie – University of Maryland, Baltimore County; 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, its accuracy as an absolute reference may be limited to several percent and it is not SI-traceable. Advancing the model to be a more accurate absolute lunar reference requires new measurements.
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, above 95% of the atmosphere. To that end, the Air-LUSI system uses a non-imaging telescope system that robotically tracks the Moon in flight, fiber-optic coupled to a stable spectrometer housed in an enclosure providing a robustly controlled environment. The spectrometer measures about 350 to 1050 nm at 3.8 nm resolution, with 0.8 nm sampling. The instrument is reproducibly stable to 0.3% and rigorously calibrated before and after campaigns and flights using a similar transfer standard spectrograph. An on-board LED source is used to monitor the instrument response during flight ascent and descent.
Air-LUSI successfully conducted a Demonstration Flight Campaign on five consecutive nights from 12 to 17 November 2019, corresponding to lunar phase angles of about 10°, 21°, 34°, 46° and 59°. Each night, the Air-LUSI system observed the Moon from above 68,000 feet altitude for 30 to 40 minutes. To reach a target uncertainty for lunar irradiance of 0.5% (k=1), processing the raw data to exo-atmospheric lunar spectral irradiance required accounting for various known behaviors of the instrument, such as thermal and stray light corrections. Additional measures were taken to address variances idiosyncratic to the campaign and were factored into the measurement error budget. The resulting error budget currently stands at less than 1% over most of the VNIR range. This paper reviews the steps taken towards high accuracy results for Demonstration Flight Campaign, how they factored in the error budget, and how our uncertainty target can be met in future campaigns.
Evaluation of air-LUSI Measurements for Constraining the ROLO Lunar Calibration Reference
Tom Stone – U.S. Geological Survey; Kevin Turpie – University of Maryland, Baltimore County; Steven Brown, Stephen Maxwell, John Woodward – National Institute of Standards and Technology (NIST)
ABSTRACT: The airborne Lunar Spectral Irradiance (air-LUSI) project is dedicated to acquiring high-accuracy, spectrally resolved measurements of the Moon from the NASA ER-2 high-altitude aircraft, flying above more than 90% of Earth's atmosphere. The air-LUSI instrument is a non-imaging system designed specifically for measuring spectral irradiance of the Moon at wavelengths from ~350 nm to 1100 nm. The project aims to achieve absolute measurement uncertainty approaching 0.5% (k=1) with traceability to NIST radiometric standards and SI. These measurements can advance lunar calibration by constraining absolute scale of models that constitute the lunar radiometric reference, such as the USGS ROLO model.
A 5-night flight campaign in November 2019 collected lunar measurements at phase angles ranging from 9.4 to 58.5 degrees after Full Moon. ROLO model outputs have been generated for the times and aircraft locations of each night's observations. Inter-night comparisons after normalizing by ROLO show inter-consistency of the measurements within 1.5%, despite a factor of 3.34 difference in lunar irradiance at 500 nm over the 5-night span. These results give no indication of an appreciable phase angle dependence in the ROLO model within the observed range. This talk will highlight implications of the high-accuracy air-LUSI measurements with regard to lunar calibration using irradiance measurements derived from lunar images acquired by space-based sensors.
1:30 pm | Advancements in Radiometric Calibration
Techniques, equipment, methods, and processes to advance the productivity and value of radiometric calibration.
Session Chair: Joe Rice, National Institute of Standards and Technology (NIST)
The FLARE Satellite/airborne Calibration Network Performance & Validation Progress Report
Brandon Russell, Jeff Holt, Will Arnold, Christopher Durell – Labsphere, Inc.; David Conran – Rochester Institute of Technology; Stephen Schiller – Raytheon Technologies, Inc.
ABSTRACT: The amount of electro-optical airborne and satellite data available today is expanding exponentially, but its inherent optical performance and signal quality is not matching pace. Better data is needed, not just more data. If “data is the new oil”, then a new tool is needed to determine where to “drill and extract” the highest and largest quantity of insights possible. Enhancing the quality of the data demands a new automated system of lower cost, practical, reliable, and high-frequency system calibration to ensure that each acquired image can be processed quickly and efficiently.
The FLARE Network is that new tool for the Cal/Val community. FLARE offers adaptable optical calibration targets to any satellite, airborne or UAV sensors on a global basis at a fractional cost of conventional calibration methods. Labsphere will detail its milestones and continued progress on the FLARE network including validation efforts and established performance against Landsat 8 and Sentinel 2A/2B. Discussion on network use and field campaigns for commercial and government satellites will be outlined and new work with UAV and airborne sensors will be discussed. Finally, the network expansion plans, expanded product offerings and future work will be detailed.
Transfer of Reflectance-based Absolute Radiometric Calibration of GE01, WV02 and WV03 to WV04 using the Libya-4 Pseudo Invariant Calibration Site in an Empirical Top-of-Atmosphere Reflectance Model
Michele Kuester, Tina Ochoa, Jared Jordan, Jeffrey Minor – Maxar Technologies
ABSTRACT: An empirical model of expected top-of-atmosphere reflectances over the Libya-4 pseudo invariant calibration site is developed by using archived Maxar imagery taken over the site between 2014 and 2021 for absolute radiometric calibration of VNIR and SWIR Earth observing sensors. For this model 212 WorldView-3 VNIR, 211 WorldView-3 SWIR, 252 WorldView-2, and 113 GeoEye-1 images were used. The images are calibrated using results from reflectance-based vicarious calibration efforts over specialized tarps at Maxar’s Ft. Lupton calibration facility. The sensor multispectral data are then transformed to hyperspectral data with the aid of NASA EO-1 Hyperion imagery over the same site and then model coefficients are derived using a Rahman-Pinty-Verstraete fit. Hyperspecial outputs of top-of-atmosphere reflectance from this model are run at relevant image acquisition times and solar and sensor view angles; and the resulting truth data are band averaged to the sensor under test. Results using WorldView-4 as the test sensor are validated over the Radiometric Calibration Network (RadCalNet) site at Railroad Valley, NV, USA (RVUS) and found to match within +/- 3%. RadCalNet is an initiative of the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites that provides SI-traceable top-of-atmosphere reflectances for post-launch radiometric calibration and validation of optical imaging sensor data. The Libya-4 site is known to change within 2-3% temporally and the reflectance-based method has a known uncertainty of less than 3%. This method can be used for sensors that have a larger ground sample distance or pixel size than can be accommodated on Maxar’s 20 x 30 m calibration tarps. It can also be used for the initial calibration of sensors launched during the winter months, when the Maxar calibration facility is not available due to weather.
Reflective Engineered Diffusers for the Roman Space Telescope Simplified Relative Calibration System
Eric Frater, Benjamin Cromey, Timothy Finch, Ray Wright, Thomas Delker – Ball Aerospace
ABSTRACT: The Wide Field Instrument (WFI) on NASA’s Roman Space Telescope (RST) has an on-board calibrator called the simplified Relative Calibration System (sRCS). The sRCS is designed to project flat-field calibration light onto the WFI focal plane in two modes of operation. One mode illuminates a quasi-Lambertian diffuser that blocks the full aperture of the telescope, and the other mode uses a small reflective engineered diffuser that sits behind each filter’s aperture mask in the WFI element wheel assembly (EWA). The second mode, called “Lamp On Lamp Off” (LOLO), uses these metallic-coated engineered diffusers to illuminate the focal plane concurrently with an exposure from the observatory and enables nonlinearity corrections. The relatively smaller size of the LOLO diffusers in comparison to the blocking diffuser motivates intentionally limiting the LOLO diffuser divergence angle to enhance flux. This presentation shows how diffuse divergence from metallic-coated engineered diffusers satisfies a nearly identical angle of incidence range at the WFI focal plane as a quasi-Lambertian diffuser. Further, it is shown that the LOLO diffusers are effective at producing a spatially uniform and smooth focal plane illumination when illuminated by a diffuse extended source.
Nonuniform Calibration Artifacts in OCO-2 and OCO-3
Robert Rosenberg, Lars Chapsky, David Crisp, Jonathan Hobbs, Graziela Keller, Richard Lee, Yuliya Marchetti, Gary Spiers, Annmarie Eldering – NASA Jet Propulsion Laboratory/California Institute of Technology; Stephen Maxwell – National Institute of Standards and Technology (NIST)
ABSTRACT: The Orbiting Carbon Observatory -2 and -3 instruments have been measuring reflected sunlight in the near infrared from low Earth orbit since 2014 and 2019 respectively. A three-channel spectrometer with common entrance optics measures narrow spectral bands centered at 765 nm for oxygen and 1608 and 2065 nm for carbon dioxide. To achieve spectral resolving power exceeding 18000:1, a diffraction grating disperses each spectrum over 1016 columns of the focal plane array. In the spatial dimension, 160 central rows are averaged into eight footprints. For accurate and precise retrievals of carbon dioxide concentration, the calibration process needs to correct for spurious features from the instrument and test sources. The cause and nature of these artifacts varies considerably, including patterns intrinsic to the detector and readout electronics, the signatures of various optical components, and contamination. Most features are accounted for by deriving independent calibration coefficients for each spectral sample, but even a single pixel can disrupt science. A machine learning classifier has been deployed to identify bad pixels in dark and lamp data that are removed in flight software. Additionally, calibrated Earth spectra are checked for outliers that can be ignored by the retrieval before retrospective products are released. These techniques are also relevant to future missions that are planning to incorporate larger format detectors.
Tuesday, August 31, 2021
8:00 am | Operational Sensor Inter-Calibration and Validation
Performance comparison between sensors of differing scientific objectives, capabilities, and mission parameters to assess measurement bias and uncertainty.
Session Chair: Michele Kuester, MAXAR
Preparation of the Calibration Baseline for Sentinel-2 Collection 1
Bahjat Alhammoud – ARGANS; Bruno Lafrance, Carine Quang – CS Group; Sebastien Clerc – ACRI-ST; Jerome Louis – Telespazio France; Bringfried Pflug – German Aerospace Center (DLR); Valentina Boccia – European Space Agency (ESA)
ABSTRACT: The Sentinel-2 mission observes the Earth in 13 spectral bands in the visible and SWIR with a repeat cycle of 5 days for each satellite unit A and B. A complete reprocessing of the Sentinel-2 archive to generate the "Collection-1" is currently under preparation. In this presentation we describe the activities performed by the Sentinel-2 Mission Performance Center to prepare the calibration baseline for Collection-1. The preparation activities involve a correction of some minor errors in the definition of the spectral response function at the beginning of the mission. A more significant change concerns the possible harmonization between the two sensors. Indeed, radiometric validation results reported by different teams confirm the presence of a small bias (around 1%) in the visible range between the satellites. Sentinel-2B is generally believed to be slightly too dark, while Sentinel-2A agrees better with other references. The presentation will describe the inter-satellite bias assessment as well as a study of the impact of a potential harmonization on Level-2 products.
The Radiometric Scaling of the MODIS and VIIRS Imagers to a Common Reference and Stability Analysis for the Next Edition of CERES Products
David Doelling – NASA Langley Research Center; Conor Haney, Rajendra Bhatt, Benjamin Scarino, Arun Gopalan – Science Systems and Applications, Inc. (SSAI)
ABSTRACT: The NASA CERES project has provided the climate quality observed TOA and computed surface fluxes to the scientific community. CERES uses MODIS and VIIRS imagers to retrieve cloud properties needed to convert Terra, Aqua, NPP, and NOAA-20 CERES footprint radiance observations into fluxes. The imagers are also used to radiometrically scale the geostationary sensors (GEO) radiances to the imager calibration reference to ensure that the GEO derived cloud properties and broadband TOA fluxes are consistent in both space and time. Both the imager and GEO retrieved cloud properties are used to compute the surface fluxes. The CERES imager and GEO calibration team uses ray-matched radiance pairs to radiometrically scale the SNPP and NOAA-20 VIIRS sensors to the Aqua-MODIS calibration reference. The radiometric scaling is further validated using geostationary imagers as transfer radiometers. The team will rely primarily on deep convective clouds to monitor the imager channel calibration stability and to correct for short term calibration drifts.
The DSCOVR satellite was launched on February 25, 2015 and orbits around the L1 Lagrange point directly between the Earth and the sun. The EPIC sensor contains no onboard calibration systems. However, multiple inter-calibration studies have shown that the EPIC imager is very stable in time. The excellent radiometric stability of EPIC allows the use of EPIC observations as a stable reference to validate both the short term drift corrections of the imagers, as well as to validate the radiometric scaling factors between them. Examples of the imager relative calibration using EPIC before and after radiometric scaling will be shown along with the results from the use of invariant targets to remove imager calibration drifts.
Sentinel-2/MSI and LANDSAT8/OLI Radiometry Intercomparison Using RadCalNet Dataset and DIMITRI-toolbox
Bahjat Alhammoud, Cameron MacKenzie – ARGANS; Sebastien Clerc – ACRI-ST; Carine Quang – CS-group; Béatrice Berthelot – Magellium; Rosario Iannone – Rhea-Group; Valentina Boccia – ESA Centre for Earth Observation (ESRIN); Marc Bouvet – ESA European Space Research and Technology Centre (ESTEC)
ABSTRACT: The Radiometric Calibration Network (RadCalNet) has been established by the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) Infrared and Visible Optical Sensors Subgroup (IVOS) in 2013 and is open to public since July 2018. The RadCalNet consists of four international test sites providing automated in situ measurements and estimates of propagated top-of-atmosphere (TOA) reflectance (Bouvet et al. 2019).
This work based on the work of Alhammoud et al. (2019) for the Sentinel-2/MSI validation; and on the work of Jing et al. (2019) to correct the directional effect. In this study we extend Alhammoud et al. (2019) analysis over RadCalNet up to 2021, instead of 2018. In addition, we will present the results of a cross-mission intercomparison over RadCalNet sites for MSI-A, MSI-B and OLI-8 using DIMITRI-Toolbox.
The results confirm the viewing angle effect in the Sentinel-2 data at the RVUS and LCFR sites. The correction of the directional effect improves the results over the ratios of the individual orbits by up to 5% -10%, while the average ratios has been improved by barely about 1%. However the intercomparison results illustrate the relevance of RadCalNet dataset for the vicarious validation activity.
Alhammoud et al. Sentinel-2 Level-1 Radiometry Assessment Using Vicarious Methods from DIMITRI Toolbox and Field Measurements From RadCalNet Database. IEEE JSTAR, 2019, Vol: 12(9)
Bouvet et al. RadCalNet: A Radiometric Calibration Network for Earth Observing Imagers Operating in the Visible to Shortwave Infrared Spectral Range. Remote Sens. 2019, 11, 2401. https://doi.org/10.3390/rs11202401
Jing et al. Evaluation of RadCalNet Output Data Using Landsat 7, Landsat 8, Sentinel 2A, and Sentinel 2B Sensors. Remote Sens. 2019, 11, 541.
Accurately Characterizing Inter-Sensor Calibration Radiometric Biases between SNPP and NOAA-20 OMPS Nadir Profiler Sensor Data Records
Banghua Yan, Trevor Beck – NOAA/NESDIS/STAR/SMCD/SCDAB; Chunhui Pan – CISESS; Ding Liang, Junye Chen – Global Science Technologies, Inc.; Jiangfeng Huang, Steven Beckner, Xin Jin – Science Systems and Applications, Inc. (SSAI)
ABSTRACT: The Ozone Mapping & Profiler Suite (OMPS) Nadir Profiler (NP), onboard both the Suomi National Polar-orbiting Partnership (SNPP) satellite and the Joint Polar Satellite System NOAA-20 satellite, is an ultraviolet-visible imaging spectrometer that measures Earth’s albedo by registering terrestrial events to Earth image and extraterrestrial events to Solar spectral images. The NP operates from wavelengths of 250 to 310 nm to profile ozone observations in Earth’s stratosphere. Through years of intensive post-launch calibrations and validations, the Sensor Data Record (SDR) data from both SNPP and NOAA-20 NP sensors demonstrate good performance, meeting the SDR specifications (e.g., Pan et al., 2017). However, it is still challenging to characterize inter-sensor calibration radiometric biases between SNPP and NOAA-20 NP due to non-negligible differences in instrument spectral features, spatial resolution, and temporal resolution. In addition, very narrow NP swath coverage of 250 km not only increases the temporal difference up to 8 days but also extremely reduces the sample size of overlapped observations between the two satellite sensors.
To accurately quantify SNPP and NOAA-20 NP inter-sensor calibration radiometric biases, our study conducts a series of analyses by taking advantage of existing inter-sensor comparison methods, such as the 32-day averaged difference method (Yan et al. 2020), the Simultaneous Nadir Overpass (SNO) method (Cao and Heidinger, 2002), and the deep convective cloud (DCC) method (Wang et al., 2020). Due to limited sample size per geographic location during collocated observations, a 32-day consecutive data set is essential in our zonal mean analysis. Such a data set provides a statistically robust feature for our inter-sensor comparison. The significance is also recognized to ensure the consistency of geographic locations in the data sets between two sensors. The data from two satellites over a similar geographic location need to be simultaneously removed if one satellite observation fails in passing a given quality-control (QC) criterion. Otherwise, resultant mismatches of observations in location can cause large geographic distance differences of over 100 km, further producing many imprecise inter-sensor radiometric bias features. Following those analyses, the impacts of viewing condition discrepancies such as solar zenith angle (SZA) difference on the inter-sensor biases will be assessed using an existing radiative transfer modeling (RTM) to improve the QC criteria in the zonal mean analysis. This is important since the SZA difference can be as large as a couple of degrees between the two NPs’ observations over a similar geographic location. Furthermore, the zonally averaged inter-sensor calibration radiometric bias features will be validated using the RTM and third sensor (e.g., OMPS Nadir Mapper or Visible Infrared Imaging Radiometer Suite) as a transfer, respectively. The validations include some relatively homogenous regions, e.g., the DCC region and open oceans. Finally, we will assess the impacts of SNPP and NOAA-20 NP sensor spectral feature discrepancies in bandpass, radiance sensitivity, wavelength shift, and polarization sensitivity on the inter-sensor biases by using the STAR Vectorized Community Radiative Transfer Model (VCRTM) (Liu and Cao, 2019) and the Algorithm Development Library (ADL) software for OMPS SDR processing.
SHARC Mission Operations, Spectro-Radiometric Calibration and Analysis
Gordon Scriven, Jesse Hayes, Jeff Defelice, John Breen, Chelsea Brown – Torch Technologies; Carey Scott, Tom Horvath, Jennifer Inman – NASA Langley Research Center
ABSTRACT: The SCIFLI Hayabusa2 Airborne Reentry Observation Campaign (SHARC) resulted in the acquisition of spectral data from a reentering capsule-type spacecraft and results are presented here. The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa2 probe in 2014 to collect samples from a C-type near-earth asteroid and return them to Earth. The Hayabusa2 sample return capsule (SRC) reentered the Earth’s atmosphere over Australia on 05 December 2020. The NASA Scientifically Calibrated In-FLight Imagery (SCIFLI) team equipped two aircraft with multiple sensors and 4-axis gimbal tracking systems to collect spectral data, aircraft positions, and sensor pointing information during the reentry. Data was successfully collected on all ten imaging spectrometers and when combined covered the UV-SWIR (300 to 1700nm) spectral range. The spectral signatures include thermal emission from the SRC and shock layer/wake emission from the ionized flowfield. These data will be used to validate selected NASA flowfield and radiance transport codes. As such, spectro-radiometrically calibrated data is required.
This paper provides a summary of the mission planning, flight operations, and the comprehensive calibration process which included pre-mission characterizations, in-flight star calibrations and post-mission calibrations. The measured signatures include traceable uncertainty bounds and the uncertainty analysis is presented. The calibrated data is shown, and interesting spectral features are discussed. Finally, the measured data is compared with the NASA model predictions.
1:15 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.
Session Chair: Asal Naseri, USU/Space Dynamics Laboratory
Radiometric Calibration of SkySats Using Near-Simultaneous Crossovers with Sentinel-2 over Calibration Sites
Hannah Bourne, Arin Jumpasut, Alan Collison – Planet
ABSTRACT: Planet Labs currently operates a fleet of 21 high resolution Earth observation satellites known as SkySats. These sub-meter resolution satellites have high intra-day revisit rate capabilities, can image scenes in a range of viewing angles, create 3D scene composites and take videos even in regions traditionally difficult to observe due to low satellite capacity. The radiometric calibration of other satellite models within Planet’s fleet (Dove Classic, Dove R and SuperDove) is currently achieved using simultaneous crossovers with Sentinel-2. Radiometric calibration of SkySat imagery using Sentinel-2 poses unique challenges as it has relatively wide spectral bands and frequently takes images off-nadir. In order to achieve optimal radiometric calibration, SkySats are tasked to image Radiometric Calibration Network (RadCalNet) and Pseudo Invariant Calibration (PIC) sites daily to generate numerous near-simultaneous crossovers of these sites with Sentinel-2. Using a reference satellite to cross-calibrate is a common approach in radiometric calibration, however bidirectional reflectance distribution (BRDF) effects may affect accuracy especially if the viewing angles of the satellites are substantially different. Here we will discuss some of the current challenges and effects of applying this approach to SkySat imagery.
Improving the Radiometric Calibration of the Heterogeneous Planet Dove Fleet using Near-Simultaneous Crossovers with Sentinel-2 and Lunar Observations
Alan Collison, Arin Jumpasut – 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. This presentation will describe the process of updating the calibration of all the Planet Dove satellites using the archive of data in preparation for a new product release to customers in the summer of 2021. The on-orbit calibration methodology will be described combining simultaneous crossovers and lunar observations as well as results using the updated calibration. Research of per-scene harmonisation with a Sentinel-2 reference will also be shown demonstrating improvements in interoperability across different satellite generations.
Radiometric Calibration of the Rogue-Alpha, Beta Short Wavelength Infrared Sensors
Jon Mauerhan, John Santiago, Paul Zittel, Dee Pack – The Aerospace Corporation
ABSTRACT: We report on the ground and on-orbit radiometric calibration of the SWIR sensors on the Rogue Alpha/Beta CubeSats. Also known as AeroCube 15 A and B, this rapid prototype constellation comprised of two 30x10x10-cm CubeSats flying commercially available InGaAs cameras, was boosted into low Earth orbit on 14 January 2020. The sensor optics are outfitted with a narrowband filter centered within the atmospheric H2O overtone absorption band near 1.4 microns. Pre-flight calibration activities in the lab at the Aerospace Corporation included characterization of sensor linearity and pixel-to-pixel uniformity through the filtered optical system, and radiometric response was derived using measurements of Lambertian scattering surfaces illuminated by incandescent sources. In-flight radiometric calibration of both the SWIR sensors and visible-wavelength context cameras were performed via observations of stars Betelgeuse, Antares, Sirius, and Vega; these stars are frequently observed by our Astronomy Field Observations team at Aerospace and their modeled spectral energy distributions are utilized for radiometric calibration of various visible and infrared sensors. A dithered pointing strategy was used for imaging, enabling timely subtraction of the dark signal. The SWIR radiometric responses derived from each star are in excellent agreement with each other, and also with the pre-flight lab radiometry. We discuss our methodology, results, application to a sample Earth image, and lessons learned for future programs.
Evaluating Radiometry within a Heterogenous Satellite Fleet Via Continuous Moon Monitoring
Michael Medford, Arin Jumpasut, Hannah Bourne, Kattia Flores Pozo – Planet
ABSTRACT: Planet currently operates a constellation of hundreds of satellites that collect multiple images of the Earth each day, constructing an historic daily catalog of the Earth’s surface taken over the past four years containing millions of images. Innovations in satellite and camera design over the past few years have resulted in a constellation containing several generations of instruments that require relative and absolute radiometric calibration to produce a seamless imaging product. We use the moon as a natural stable reference unencumbered by atmospheric effects present while nadir imaging and have amassed a database of over nine millions images of the moon taken by all of the satellites within our fleet since Q4 of 2016. We will present results on our lunar processing pipeline that leverages routinely automated near simultaneous imaging of the moon over the entire constellation to reduce intra-flock variations. We will discuss how lunar images help us detect hazing and scattered stray light across the image plane, as well as monitor imaging stability over our instruments’ lifetime.
ACCURACy: Adaptive Calibration of Cubesat Radiometer Constellations
John Bradburn, Henry Ashley, Mustafa Aksoy – University at Albany, SUNY
ABSTRACT: Recent technological advancements enable the cost-effective deployment of constellations of CubeSats. Constellations of radiometer equipped CubeSats have great potential for use in scientific missions for remote sensing objectives including weather tracking and storm imaging, climate change measurement, and atmospheric science, to name a few. While CubeSats provide a solution to challenges in cost, weight, and power, there exist drawbacks which make radiometer calibration more difficult, specifically due to increased sensitivity of the instrument to ambient conditions, resulting from the lack of an adequate thermal control system. To address this problem, a novel, constellation-level calibration framework is being developed called “Adaptive Calibration of CubeSat Radiometer Constellations (ACCURACy)”. ACCURACy clusters radiometers together using instrument-level telemetry data to identify radiometers in similar states, leveraging a relationship between radiometer gain and instrument telemetry data. These clusters are used to identify when radiometers make calibration measurements while in similar states and store these calibration measurements and times in calibration pools to calibrate other radiometers that are in a similar state in the future. This paper discusses the development of ACCURACy including a MATLAB framework and radiometer data simulator, as well as the performance of ACCURACy compared to current state of the art calibration techniques for constellations of CubeSats.
Wednesday, September 1, 2021
8:00 am | 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.
Session Chair: Bahjat Alhammoud, ARGANS
The STAR-CC-OGSE System for Pre-flight Sensor Calibration
Paul Green, Christopher Baker, Sean Devlin, William Kingett, Nigel Fox – National Physical Laboratory
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.
The STAR-CC-OGSE has completed the performance tests and is currently in use with the performance validation of the CNES/UKSA MicroCarb sensor. This paper will describe the STAR-CC-OGSE system, the outcome of the verification testing and system performance.
The Reduced Background Calibration Facility 2 for Infrared Detectors, Cameras, Sources and Small Satellites
Christian Monte, Max Reiniger, Albert Adibekyan, Christoph Baltruschat, Jonas Bories, Julian Gieseler, Berndt Gutschwager, Robert Häfner, Ingmar Mäller, Jörg Hollandt – Physikalisch-Technische Bundesanstalt
ABSTRACT: The Physikalisch-Technische Bundesanstalt (PTB) designed a new calibration facility, the Reduced Background Calibration Facility 2 (RBCF2) and brought it recently into operation. It provides traceable calibrations of air born and space based infrared remote sensing experiments in terms of radiance temperature and spectral radiance. Traceable measurements from space require the use of calibrated stable detector systems and/or source-based calibration standards on board of the instrumentation. In any case they should be calibrated under space like conditions to ensure traceability with the smallest possible uncertainty. The RBCF2 enables therefore the calibration of radiators and detectors and cameras under cryogenic and/or vacuum conditions. The integration of the instrument under test into the RBCF2 can be done under ISO 5 clean room conditions.
The general concept of the RBCF2 is to connect different sources in the source chamber and detectors in the detector chamber via a liquid nitrogen cooled beam line. Source and detector chamber also incorporate cooling facilities. Translation units in both chambers enable the RBCF2 to automatically compare and calibrate different sources and detectors with stable comparison instruments at cryogenic ambient temperatures and under a common vacuum. Reference sources for comparisons are dedicated vacuum variable temperature blackbodies, for example the vacuum medium temperature blackbody (VMTBB, 150 °C to 430 °C), the vacuum low temperature blackbody (VLTBB, -173 °C to 177 °C), the large area heatpipe blackbody (LAHBB, -60 °C to 50 °C) featuring a radiating diameter of 250 mm, the liquid nitrogen blackbody (LNBB, -196 °C) and calibrated vacuum integrating sphere radiators for UV-VIS and SWIR applications. The radiation temperatures of the reference blackbodies and the radiance of the integrating sphere radiators are traceable to the ITS-90 via the primary standards of PTB. Using the calibrated vacuum infrared standard radiation thermometer (VIRST) direct calibrations of sources in terms of radiance temperature in the wavelength range from 8 µm to 14 µm can be performed.
For spectrally resolved measurements the radiation of the reference sources and the sources under test is imaged on a vacuum Fourier-Transform Spectrometer (FTS). The FTS covers the wavelength range from 0.4 µm to 1000 µm by employing detectors ranging from photomultipliers to liquid helium cooled bolometers. The different reference blackbodies enable measurements with respect to at least two reference temperatures, simultaneously. Hereby disturbances in the IR by background radiation resulting from inside the FTS can be effectively compensated. Sources can be also spatially mapped and characterized for the lateral distribution of their spectral radiance. The flexible design of the facility also allows large aperture camera characterizations and modifications for customer needs and the measurement of directional spectral emissivities over a wide temperature and wavelength range.
Recent calibrations of the large aperture on-board blackbodies of the airborne GLORIA limbsounder, the on-board calibrations assembly (OBCA) of the EnMAP satellite and of the prototype on-board blackbody for FORUM mission are shown to illustrate the capabilities.
Room Temperature Self-Calibrating Optical Power Detector for On-site Calibrations
Marit Ulset Nordsveen, Jarle Gran – Justervesenet; Eivind Bardalen – University of Southeastern Norway
ABSTRACT: Low cost, high-accuracy calibration standards are requested by the radiometry community . In the EMPIR-funded project chipS·CALe, we are developing self-calibrating dual-mode detectors for high-accuracy optical power measurements to meet this need. The dual-mode detector combines two primary standard techniques (PQEDs and electrical substitution radiometer ) into one device. This means the detector can be calibrated against its own internal primary reference. This eliminates the usually long and cumbersome traceability chain, and makes the detector suitable for calibrations in remote locations.
The absorbing element for both measurement modes is an induced-junction photodiode . A photodiode has internal losses that make it deviate from ideal responsivity. These losses vary with temperature and wavelength, and change over time as material properties of the photodiode change. As they affect the responsivity of the photodiode, the internal losses must be determined before high-accuracy measurements can be done. In the dual-mode detector these internal losses are determined by using thermal mode as a reference. In addition, an independent method for determining the internal losses is available, by fitting a charge carrier simulation model to IV curves .
To have the dual-mode detector work in thermal mode, special packaging of the photodiode is required . The silicon photodiode is mounted on a carrier with a weak thermal heat link. The thermal design of the detector is optimised to minimise non-equivalence between optical and electrical heating, by the use of COMSOL heat transfer simulations. Vacuum conditions are necessary, as heat convection through air introduces complicated and unpredictable effects on the thermal equivalence. The largest contributor to non-equivalence is radiation losses, due to different thermal gradients in electrical and optical heating mode.
Halfway through the project, we have already reduced the type A uncertainty below the project aim of 0.05 % in room temperature, getting close to uncertainty levels comparable to primary standard cryogenic radiometers. We are continuously making improvements in thermal packaging, thermal readout, electrical readout and calculation algorithms, and the latest results will be presented at the conference.
This project 18SIB10 chipS·CALe 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.
Figure 1: Two of our dual-mode detector modules. During operation they are mounted in a trap configuration in the construction visible in the background, to minimise reflection losses.
 CCPR Strategy Document, Ch. 5.2.1 https://www.bipm.org/utils/en/pdf/CCPR-strategy-document.pdf
 BIPM. Mise en pratique for the definition of the candela in the SI, Ch 5.1 http://www.bipm.org/en/publications/mises-en-pratique, 2019.
 T. E. Hansen. Silicon UV-Photodiodes Using Natural Inversion Layers. Physica Scripta, 18:471-475, 1978.
 J. Gran, T. Tran and T. Donsberg. Three dimensional modelling of photodiode responsivity. 14th International Conference on New Developments and Applications in Optical Radiometry (NEWRAD 2021)
 E. Bardalen, M. U. Nordsveen, P. Ohlckers, and J. Gran. Packaging of silicon photodiodes for use as cryogenic electrical substitution radiometer. 14th International Conference on New Developments and Applications in Optical Radiometry (NEWRAD 2021)
The SUNSOURCE: Direct solar-view radiance levels for absolute calibration
Matthew Birkebak, Paul Mascia, Joseph Jablonski, Christopher Durell, Joshua Hudson – Labsphere, Inc.
ABSTRACT: The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored satellite mission that is providing state-of-the-art measurements of incoming x-ray, ultraviolet, visible, near-infrared, and total solar radiation. Labsphere was contracted by Laboratory for Atmospheric and Space Physics (LASP) to build a radiant uniform calibration source for the next-generation SORCE replacement iinstrument that had a high fraction of a direct view of the sun at the top of the atmosphere. The aperture of the system was 1” to fractionally fill the field of view (FOV) of the next generation SORCE instrument for solar observation and calibration. This presentation will exhibit the design parameters of the source using Labsphere’s PEL Plasma sources and QTH lamps and a unique fiberoptic delivery structure. A peak radiance of 1.121e+4 uW/cm2-sr-nm was achieved without a spatial diffuser and 2.984e+3 uW/cm2-sr-nm was achieved at 600nm with a diffuser. Uniformity and stability performance will be reported both during construction and validation as well as further test results developed at the customer’s site.
Thursday, September 2, 2021
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.
Session Chair: David Doelling, NASA Langley Research Center
Lessons Learned from Operation of On-board Calibration Devices on Sentinel-2 MSI and Sentinel-3 OLCI
Sebastien Clerc, Ludovic Bourg – ACRI-ST
ABSTRACT: Sentinel-2 MSI and Senitnel-3 OLCI are two visible imagers contributing to the European Copernicus Earth Observation program. Both instruments are periodically calibrated using on-board Sun diffusers. OLCI has two Sun diffusers (nominal and reference diffuser), while MSI has only one. OLCI uses a shutter to perform dark signal calibration, while MSI relies on nigtht-time acquisitions over the Ocean. Finally, OLCI has a coloured diffuser for spectral response monitoring.
Two Sentinel-2 and 3 units each are currently flying, with the A units achieving 5 years of operation. The purpose of this presentation is to draw some conclusions from the flight experience and provide recommendations for the future. This activity is performed in the frame of the Copernicus Cal/Val Solution project, which aims at a holistic solution for the calibration and validation of present and future Sentinel missions.
For both OLCI and MSI, the on-board dffusers have proved a reliable and efficient calibration source. No operational issue was encountered, and the diffusers seem remarkably stable over 5 years. However some limitations have been observed. First, inaccuracies in the BRDF characterization lead to seaonnal artifacts on the absolute and relative (in the field) gains.
The second point concers the existence of radiometric biases between the different satellites although they share a common calibration approach. This is even the case for satellites of the same family (2.5% radiometric bias between OLCI-A and B, 1% between MSI-A and B). Although these biases are not very large, they point to a room for improvement in the characterization of the diffuser and the verification of the global uncertainty budget.
The presentation will also address lessons learned from other calibration techniques (dark and spectral). We conclude with some recommendations for future Sentinel missions:
- the characterization of the diffuser should be imporved and made more traceable.
- an in-flight characterization of the BRDF (using satellite yaw manoeuvres) shall be performed during commissioning operations
- the global uncertainty budget for the diffuser should be established according to common standards, and be made available to cal/val users.
This project has received funding from the European Union’s Horizon 2020 research and innovation programe under the grant agreement No 101004242.
Pre-Flight Calibrations for the PIANO Airglow Camera on the ISS
Amanda Bayless, Richard Rudy, Lynette Gelinas, James Hecht, Dave Gutierrez, Kirk Crawford – The Aerospace Corporation
ABSTRACT: The Phenomenology Imager and Nighttime Observer (PIANO) is an infrared imager that, through the auspices of the Space Test Program (STP), is scheduled to fly on the International Space Station (ISS) in December 2021 on the STP-H7 instrument pallet. It will be among the first 4k x 4k IR focal planes flown in space. It uses the Teledyne H4RG detector and a custom optical assembly to obtain a high native spatial resolution of about 65 m per pixel at the ground. The FPA is cooled by a tactical cryocooler to temperatures of less than 150K and operates at 1.5 to 1.72 microns (similar to the H band). PIANO will observe nighttime weather and cloud types as well as studying the Earth’s airglow and wave structures in the upper atmosphere. The precursor to PIANO, the Near-Infrared Airglow Camera, with a 2k x 2k IR focal plane, launched in May 2019 and is still operating onboard the ISS.
This presentation discusses pre-launch testing results of PIANO. These tests include characterizations to optimize the performance of the focal plane, which has a cut-off wavelength of 1.72 microns, and radiometric calibration incorporating the flight optics and obtained with both in-laboratory sources and star fields.
Mitigation of Calibration Anomaly for GOES-17 ABI Infrared Images Before Local Midnight
Fangfang Yu, Haifeng Qian – University of Maryland; Xiangqian Wu – NOAA/NESDIS/STAR; Jon Fulbright – Arctic Slope Technical Services, Inc
ABSTRACT: In February 2021, a GOES-17 Advanced Baseline Imager (ABI) infrared (IR) image with a stripe near the Equator came to our attention. It was found later that this abnormal feature also occurs on some other days for several IR channels, and the location of the anomaly changes with the ABI scan modes. Further characterization revealed that this calibration anomaly can be observed when the Focal Plane Module (FPM) temperature is stable, the predictive calibration (pCal) algorithm is enabled, and before the satellite midnight. The pCal algorithm is the adopted ABI IR operational calibration algorithm to mitigate the GOES-17 Loop Heat Pipe (LHP) anomaly. We found that it can cause relatively large erroneous calibration coefficient values at certain swaths in a timeline when it is enabled in the stable FPM time before satellite midnight, resulting in the stripe near the Equator. A related but previous unnoticed anomaly was also found during this investigation. These calibration anomalies can be reduced in operation with a new operational pCal turn-on scheme. The operational mitigation effort is undergoing.
Estimation of VIIRS On-Orbit TEB Response Versus Scan and Zero Offsets Using Pitch Maneuver Data
Wenhui Wang – University of Maryland - College Park; Changyong Cao – NOAA/NESDIS/STAR; Slawomir Blonski – Global Science & Technology, Inc
ABSTRACT: The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) and the National Oceanic and Atmospheric Administration - 20 (NOAA-20) satellites provide state-of-art global Earth observations for a wide variety of environmental and climate applications. Larger than expected scan angle and scene temperature dependent biases were observed in NOAA-20 VIIRS Thermal Emissisve Bands (TEB) data from the NOAA operational processing. This issue needs to be addressed to support user communities.
This study presents an improved method for estimating VIIRS TEB Response Versus Scan (RVS) and zero offsets (c0 coefficients) using on-orbit pitch maneuver data. First guess on-orbit RVS values at Earth View (EV) and Space View (SV) angles of incidence (AOI) on the half angle mirror (HAM) are estimated using TEB calibration equations with prelaunch calibration coefficients (Wang et al. 2019, Step 1). Then corrections to zero offsets are derived using the prelaunch test based 2nd order polynomial curve assumption for RVS (Step 2). Finally, TEB RVS at all AOIs and zero offsets are optimized iteratively by repeating Steps 1 and 2, using improved RVS and zero offsets. Compared to the Wang et al. 2019 study, the pitch maneuver data derived RVS derived in this study is not affected by errors in the prelaunch zero offsets. The improved method was validated using reprocessed VIIRS Sensor Data Records (or Level 1B data) and independent co-located Cross-track Infrared Sounder (CrIS) observations, as well as over the Dome-C site. Preliminary VIIRS-CrIS brightness temperature biases for bands M13, M15-M16, and I5 indicate that the improved method can effectively reduce the NOAA-20 scan angle and scene temperature dependent biases. Evaluation results over the Dome-C site show that S-NPP M15 and M16 striping at cold scene temperatures can also be significantly reduced.