The JPSS-2 VIIRS instrument is set to be the third VIIRS instrument when it launches in 2022 following S-NPP and NOAA-20 VIIRS which launched in October 2011and November 2017, respectively. To date JPSS-2 VIIRS has undergone extensive pre-launch testing at the instrument system level to determine the radiometric, spatial, and spectral performance. Spectral testing was conducted by the instrument vendor, Raytheon Corporation, at their test facility in mid-to-late 2017 with a test configuration that utilized a double monochrometer with illumination provided by tungsten lamp and ceramic glow bar to cover the full spectral range. The purpose of these measurements was to measure the relative spectral response curve and assess the spectral characteristics necessary to determine compliance with the sensor design requirements. In addition to Raytheon team, the spectral measurements were analyzed by an independent government team with members from NASA, the University of Wisconsin, and Aerospace Corporation. Two RSR curves were released by the government team from this data set: a version 0 release which was the verified RSR as calculated by Raytheon, and version 1 which was the RSR assessment from the government team. The results discussed here are those of the government team (version 1) including the independent assessment of sensor compliance and a comparison of the JPSS-2 VIIRS spectral characteristics with the two previous VIIRS instruments. The version 1 RSR was publically released to the science community in the fall of 2018, and remains available for their use.
The stray light contamination of the VIIRS Day-Night-Band (DNB) on-board the S-NPP satellite has been studied intensively. To alleviate its impact, a stray light correction look-up-table (LUT), which represents the stray light contamination, is derived from the new moon night dataset by subtracting the non stray light signal from the stray light affected signal. The derived LUT can be used to remove the majority of the contamination. However, the LUT remains static until the next update to the Level-1B data processing, usually one month later. Between these two updates, changes in the actual stray light are not captured. We present a method to derive a dynamic stray light correction LUT that covers the time period between updates. By analyzing the patterns in the annual stray light variation, a consistent trend was found in the LUT’s characteristic features which can be quantitatively expressed as time factors. These factors are then applied to the monthly LUT to produce a dynamic stray light LUT for any time of interest. The L1B software can use this algorithm to calculate the LUTs at the time of observation. The results show significant improvement in the DNB product compared to using the monthly static LUT. Furthermore, this time-dependent algorithm provides a basis for deriving a universal stray light correction LUT for VIIRS.
The JPSS-2 VIIRS sensor has completed its pre-launch test program and is now awaiting launch in the 2022 timeframe. The VIIRS spectral characterization, in the form of band averaged and supporting detector level relative spectral response (RSR) for each VIIRS band, was completed in 2019 and is based upon independent SpMA dual monochromator (all bands) and GSFC GLAMR laser system (reflectance bands only) spectral measurements, including first time measurements of the VIIRS SWIR bands by a laser system. The measurements and subsequent analysis effort by subject matter experts of the VIIRS DAWG has led to the July 2019 VIIRS Version 2 RSR release, the official at-launch RSR characterization for the JPSS-2 VIIRS mission. Version 2 replaces and improves upon the August 2018 Version 1 release by incorporating the GLAMR measurements into the analysis to produce an updated “fused” RSR for reflective solar bands (M1- M10, I1-I3, DNBLGS, DNBMGS) and by applying a CO2 absorption correction to the SpMA measurements for thermal band M13. For all other bands (M11, M12, M14-M16, I4, I5), the Version 1 characterization, based entirely upon the SpMA measurements, is carried forward into the Version 2 release. An assessment on compliance with spectral performance metrics finds that VIIRS is compliant on nearly all metrics, with a few minor exceptions. The version 2 RSR release includes band average (over all detectors and subsamples) RSR plus supporting RSR for each detector and subsample, and is available under EAR99 restrictions to the science community at a restricted access NASA eRoom site.
In this paper, we report a new method for calculating the S-NPP VIIRS Day-Night-Band (DNB) detector dark offsets and gains look-up-tables. During the seven years of S-NPP operation, the NASA VIIRS Characterization Support Team (VCST) has generated detector gain and dark offset calibration coefficients to be used in the DNB L1B Earth view radiance retrieval.[1,2] There have been a few calibration algorithm updates during the mission, however, those changes were only applied to the L1B forward processing. In preparation for reprocessing the L1B data for the entire mission using a consistent calibration method, we have regenerated the DNB gains and dark offset coefficients for the entire mission by integrating all the algorithm updates. The newly obtained gain and dark offset coefficients curve fits as functions of time are smoother than the previous versions. The amplitude of the oscillatory features in the high gain stage calibration fits have been greatly reduced. The preliminary test results show improvements on the DNB Earth view images as expected.
The VIIRS instrument captures reflected solar or emitted thermal radiation from the Earth in selected wavelengths. Each wavelength is covered by a band of detectors. Some bands are dual gain and conduct measurements in a more sensitive high gain (HG) stage for enhanced resolution in the lower radiance range, and transit to a low gain (LG) stage for the higher radiance. A slight discontinuity in the derived radiance can be observed around the gain transition, with calibrated radiance values that appear either missing or duplicated in both gains. This paper illustrates that the gain transition discontinuity (GTD) is a side effect of the on-orbit calibration method, and shows a possible way to adjust the calibration coefficients to make the LG and the HG results more consistent under certain conditions. The nonlinear behaviors of the calibrated results around the GTD that are not captured during the pre-launch test are also revealed. Because of the complexity and uncertainty in the on-orbit calibrations, we recommend to improve the pre-launch test to characterize the GTD in advance.
The JPSS-2 VIIRS instrument much like its predecessors JPSS-1 VIIRS (now renamed NOAA-20) and S-NPP VIIRS has an innovative three gain stage Day-Night Band (DNB) will provide high quality imagery of the Earth over a wide range of illumination conditions. This band uses a set of four CCDs and 32 different aggregation modes of time-delay integration and sub-pixel aggregation to achieve high SNR in low light conditions and maintain roughly constant spatial resolution across scan. In support of at launch readiness, JPSS-2 VIIRS DNB has undergone a series of prelaunch tests to characterize its spatial, radiometric, spectral, and functional performance at the instrument level and additional planned tests once integration with the spacecraft is complete. The DNB radiometric measurements were completed in October 2017 at the instrument level by Raytheon Company and subsequently analyzed by both vendor and government teams. These analyses form the basis of showing compliance with the sensor design specifications as well as the ability of the DNB to produce high quality imagery and radiometry similar to the first two missions. Presented in this work is the radiometric and spectral performance of the DNB including dynamic range, sensitivity, radiometric uncertainty and nonlinearity along with a discussion of the potential impact to on-orbit calibration and SDR performance.
The JPSS-1 (now named NOAA-20) VIIRS instrument has successfully operated since its launch in November 18, 2017. A panchromatic channel onboard NOAA-20 VIIRS is called the day-night band (DNB). With its large dynamic range and high sensitivity, the DNB detectors can make observations during both daytime and nighttime. However, the DNB night image quality is affected by the straylight contamination. In this study, we focused on Earth view data in the mid-to-high latitude of the northern and southern hemispheres when spacecraft is crossing the day/night terminators at the beginning of NOAA-20 mission. Based on on-orbit data analysis from previous VIIRS sensor onboard S-NPP mission, straylight contamination mainly depends on the Earth-Sun-spacecraft geometry, and it is also detector and scan-angle dependent. Inter-comparison investigation of straylight behavior in both SNPP and NOAA-20 instruments will be conducted to better understand straylight characteristics. The preliminary study has been performed in this paper to mitigate straylight contamination for NOAA-20VIIRS DNB night images. The effectiveness of the straylight correction algorithm, directly adapted from the S-NPP DNB, is assessed for night images in the day/night terminators. Further work has been identified to improve current straylight correction methodology and DNB-based environmental data products.NOAA-20.
The JPSS-1 (now named NOAA-20) VIIRS instrument has been successfully operating on orbit since November 28th, 2017. The Day-Night Band (DNB) is a panchromatic channel covering wavelengths from 0.5 to 0.9 m that is capable of observing the Earth scene in visible/near-Infrared spectral range at spatial resolution of 750 m. The DNB operates at low, mid, or high radiometric gain stages, and it uses an onboard solar diffuser (SD) panel for low gain stage calibration. The SD observations also provide a mean to compute gain ratios between low-to-mid and mid-to-high gain stages. With their large dynamic range and high sensitivity, the DNB detectors can make observations during both daytime and nighttime. This paper provides an early assessment of the DNB on-orbit performance and behavior in the first 90-day post launch test (PLT) period and beyond. The calibration methodology used by the VIIRS Characterization Support Team (VCST) in support of the NASA earth science community will be presented. The trending of OBC dark-offsets, SD gains and gain ratios, and signal-to-noise ratio (SNR) at minimum radiance have been analyzed, especially during key events such as the Nadir and Cryo-cooler doors opening. Furthermore, we performed inter-comparison studies between SNPP and JPSS-1 instruments and evaluated DNB radiometric calibration and characterization, including the SD degradation, detector gains and gain ratios, as well as the calibration comparison between the IDPS LUTs and our VCST delivery results.
We describe the methodology for predicting the S-NPP VIIRS Day-Night-Band (DNB) detector gains and dark offsets. During the first 5 years of operation, the DNB has shown recognizable patterns in these calibration parameters. These patterns can be decomposed into two distinctive components: degradation and oscillation. We fit the historical data using a periodic function of time superimposed on an exponential function of time to capture both sources of the variation. The results of the fit showed good agreement with the measured data, indicating that the functions may be useful as a forward model for predicting these calibration parameters for calibration updates. As a test, predictions made in April, 2016 were examined against newly obtained measurement data at monthly intervals. Through April, 2017, the prediction errors have been smaller than 1.5% in the gains and 0.5% in the offsets, with the largest errors observed in the end-of-scan aggregation modes of the high-gain stage. The oscillatory features seen in the measured gains will be analyzed to isolate possible causes and to determine the relevance of its inclusion in the model. Comparisons with the results using the existing predictions of the gain and offset Look-Up-Tables (LUTs) will also be presented.
The VIIRS Day-Night-Band (DNB) is a panchromatic band with three gain stages used for delivering imagery under conditions ranging from daylight to low light nighttime scenes. Early in the S-NPP mission a gray haze was observed in some nighttime DNB imagery with the cause determined to be stray light contamination. This effect was characterized along with a proposed correction algorithm. The correction algorithm was subsequently included in operational data processing and re-processing. However, in order to process real-time data, prediction of the stray light correction is necessary. In this paper we present a new method to predict the DNB stray light correction Look-Up-Tables (LUTs). Since measurements suitable for characterizing the stray light contamination are sparse (about once a month during new-Moon), and because some of the measurements might not be accurate due to the presences of unaccounted light sources, such as algae glow and lightening, we have applied additional constraints to the model by assuming that certain patterns of the stray light are repeatable. Comparisons of the LUT parameters produced by the prediction algorithm with those from the measurements will be presented along with the impact on the derived Earth View products.
We present system-level responsivity calibration results of the visible and near infrared channels of JPSS-1 VIIRS in the reflective solar band (RSB) from bands M1( 412 nm) to M7 (865 nm). A monochromator-based method based on the Spectral Measurement Assembly (SpMA), and a laser-based calibration method based on Travelling-Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (T-SIRCUS) were applied with different illumination methods to obtain the relative and absolute spectral responses (RSR and ASR). The spectral features of RSR for each band are verified by comparing to the component-level spectral transmittance of the VIIRS bandpass filters. Variation of RSR results of a single pixel/detector with respect to the band-averaged for each band is also investigated. Utilization of RSR results from SpMA and T-SIRCUS with different illumination methods as well as the component transmittance results enables us to recognize optical and electrical cross-talk from out-of-band, which is estimated at about 3 %. We also attempted to use the ASRs from T-SIRCUS to validate the gain coefficients derived from an independent radiometric calibration test using a broadband source. Three spectral shapes of flat spectral radiance, Tungsten lamp, and solar emission are used to simulate different scenarios for baseline, pre-launch calibration, and on-orbit calibration to verify the radiometric coefficients with the more accurate NIST-traceable calibration.
The Visible Infrared Imaging Radiometer Suite (VIIRS) is a scanning radiometercontaining 22 spectral bands that is currently collecting data aboard the Suomi-NPP satellite. A second flight unit is set to launch aboard the JPSS-1 satellite in the 4th quarter of 2017 followed by a third one aboard JPSS-2 in 2022. The VIIRS sensor is designed to obtain high quality data products over a variety of conditions including high contrast scenes like bright clouds over ocean for example. In the pre-launch test program the vendor, Raytheon, made measurements to determine the contamination from Near Field Response (NFR), which is scattered light from bright targets, to characterize these features and compare them against the structured scene requirement. As of now prelaunch testing has been completed on the first three VIIRS flight units, S-NPP, JPSS-1 and JPSS-2, with independent analyses performed by the NASA VCST team. We present this NFR characterization including derivation of the Harvey-Shack coefficients and impacts from other contamination such as retro reflections off the dewar to the cold focal planes.
The relative spectral response (RSR) characterization of the JPSS-1 VIIRS spectral bands has achieved “at launch” status in the VIIRS Data Analysis Working Group February 2016 Version 2 RSR release. The Version 2 release improves upon the June 2015 Version 1 release by including December 2014 NIST TSIRCUS spectral measurements of VIIRS VisNIR bands in the analysis plus correcting CO2 influence on the band M13 RSR. The T-SIRCUS based characterization is merged with the summer 2014 SpMA based characterization of VisNIR bands (Version 1 release) to yield a “fused” RSR for these bands, combining the strengths of the T-SIRCUS and the SpMA measurement systems. The M13 RSR is updated by applying a model-based correction to mitigate CO2 attenuation of the SpMA source signal that occurred during M13 spectral measurements. The Version 2 release carries forward the Version 1 RSR for those bands that were not updated (M8-M12, M14-M16A/B, I3-I5, DNBMGS). The Version 2 release includes band average (over all detectors and subsamples) RSR plus supporting RSR for each detector and subsample. The at-launch band average RSR have been used to populate Look-Up Tables supporting the sensor data record and environmental data record at-launch science products. Spectral performance metrics show that JPSS-1 VIIRS RSR are compliant on specifications with a few minor exceptions. The Version 2 release, which replaces the Version 1 release, is currently available on the password-protected NASA JPSS-1 eRooms under EAR99 control.
The first Joint Polar Satellite System (JPSS-1 or J1) mission is scheduled to launch in January 2017, and will be very similar to the Suomi-National Polar-orbiting Partnership (SNPP) mission. The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the J1 spacecraft completed its sensor level performance testing in December 2014. VIIRS instrument is expected to provide valuable information about the Earth environment and properties on a daily basis, using a wide-swath (3,040 km) cross-track scanning radiometer. The design covers the wavelength spectrum from reflective to long-wave infrared through 22 spectral bands, from 0.412 μm to 12.01 μm, and has spatial resolutions of 370 m and 740 m at nadir for imaging and moderate bands, respectively. This paper will provide an overview of pre-launch J1 VIIRS performance testing and methodologies, describing the at-launch baseline radiometric performance as well as the metrics needed to calibrate the instrument once on orbit. Key sensor performance metrics include the sensor signal to noise ratios (SNRs), dynamic range, reflective and emissive bands calibration performance, polarization sensitivity, bands spectral performance, response-vs-scan (RVS), near field response, and stray light rejection. A set of performance metrics generated during the pre-launch testing program will be compared to the sensor requirements and to SNPP VIIRS pre-launch performance.
This paper presents a robust method for determining the calibration coefficients in polynomial calibration equations, and discusses the corresponding calibration uncertainties. An attenuator method that takes into account all measurements with and without an attenuator screen was used to restrict the impact of the absolute calibration of the light source. The originally proposed procedure attempts to simultaneously determine all unknowns nonlinearly using polynomial curve fitting. The newly proposed method divides the task into two simpler parts. For example, in the case of a quadratic calibration equation, the first part becomes a quadratic equation solely for the transmittance of attenuator, which has an analytical solution using three or four sets of measurements. Additionally, it is straightforward to determine the median value and the standard deviation of the transmittance from the solutions using all combinations of measured data points. In conjunction, the second part becomes a linear fit, with the ratio of the zeroth-order to first-order calibration coefficients as the intercept and the ratio of the second-order to first-order calibration coefficients as the slope. These ratios are unaffected by the absolute calibration of the light source and are then used in the calibration equation to calculate the first-order calibration coefficient. How the new method works is straightforward to visualize, which makes its results easier to verify. This is demonstrated using measurements from the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) reflective solar bands (RSB) pre-launch testing.
The Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the first Joint Polar Satellite System (JPSS) completed its sensor level testing on December 2014. The JPSS-1 (J1) mission is scheduled to launch in December 2016, and will be very similar to the Suomi-National Polar-orbiting Partnership (SNPP) mission. VIIRS instrument was designed to provide measurements of the globe twice daily. It is a wide-swath (3,040 km) cross-track scanning radiometer with spatial resolutions of 370 and 740 m at nadir for imaging and moderate bands, respectively. It covers the wavelength spectrum from reflective to long-wave infrared through 22 spectral bands [0.412 μm to 12.01 μm]. VIIRS observations are used to generate 22 environmental data products (EDRs). This paper will briefly describe J1 VIIRS characterization and calibration performance and methodologies executed during the pre-launch testing phases by the independent government team, to generate the at-launch baseline radiometric performance, and the metrics needed to populate the sensor data record (SDR) Look-Up-Tables (LUTs). This paper will also provide an assessment of the sensor pre-launch radiometric performance, such as the sensor signal to noise ratios (SNRs), dynamic range, reflective and emissive bands calibration performance, polarization sensitivity, bands spectral performance, response-vs-scan (RVS), near field and stray light responses. A set of performance metrics generated during the pre-launch testing program will be compared to the SNPP VIIRS pre-launch performance.
The JPSS-1 VIIRS instrument completed sensor level testing, including spectral characterization, at the Raytheon El Segundo facility in 2014. Spectral subject matter experts (SMEs) of the VIIRS DAWG have reviewed and analyzed the spectral measurements leading to a Version 1 release of JPSS-1 VIIRS relative spectral response (RSR) data in June 2015. The analysis demonstrates that all bands are well characterized with minor performance specification non-compliances in a few bands similar to those seen on S-NPP VIIRS. A major reduction in the out-of-band response (compared to that seen for S-NPP) has been realized through the redesign of the JPSS-1 VIIRS integrated filter assembly for the warm focal plane bands. An EAR99 restricted DAWG Version 1 release consisting of detector and band average (over all detectors) in-band + out-of-band RSR for all VIIRS bands is available on the NASA JPSS-1 eRoom limited access site and replaces the previous Version 0 Beta release.
The Suomi National Polar-orbiting Partnership (S-NPP) satellite was successfully launched on October 28,
2011, beginning the on-orbit era of the Visible Infrared Imager Radiometer Suite (VIIRS). In support of atlaunch
readiness, VIIRS underwent a rigorous pre-launch test program to characterize its spatial, radiometric,
and spectral performance. Spectral measurements, the subject of this paper, were collected during instrument
level testing at Raytheon Corp. (summer 2009), and then again in a special spectral test for VisNIR bands
during spacecraft level testing at Ball Aerospace and Technologies Corp. (spring 2010). These spectral
performance measurements were analyzed by industry (Northrop Grumman, NG) and by the Relative Spectral
Response (RSR) subgroup of the Government team, (NASA, Aerospace Corp., MIT/Lincoln Lab, Univ.
Wisconsin) leading to releases of the S-NPP VIIRS RSR characterization by both NG and the Government
team. The NG RSR analysis was planned to populate the Look-Up-Tables (LUTs) that support the various
VIIRS operational products, while the Government team analysis was initially intended as a verification of
the NG RSR product as well as an early release RSR characterization for the science community’s pre-launch
application. While the Government team deemed the NG December 2010 RSR release as acceptable for the
“at-launch” RSR characterization during the pre-launch phase, the Government team has now (post-launch
checkout phase) recommended for using the NG October 2011 RSR release as an update for the LUTs used in
VIIRS SDR and EDR operational processing. Meanwhile the Government team RSR releases remain
available to the community for their investigative interests, and may evolve if new understanding of VIIRS
spectral performance is revealed in the S-NPP post-launch era.
The VIIRS Flight 1 (F1) instrument completed sensor level testing, including relative spectral response
(RSR) characterization in 2009 and is moving forward towards a launch on the NPP platform late in 2011.
As part of its mandate to produce analyses of F1 performance essentials, the VIIRS Government Team,
consisting of NASA, Aerospace Corp., and MIT/Lincoln Lab elements, has produced an independent (from
that of industry) analysis of F1 RSR. The test data used to derive RSR for all VIIRS spectral bands was
collected in the TVAC environment using the Spectral Measurement Assembly (SpMA), a dual
monochromator system with tungsten and ceramic glow bar sources. These spectrally contiguous
measurements were analyzed by the Government Team to produce a complete in-band + out-of-band RSR
for 21 of the 22 VIIRS bands (exception of the Day-Night Band). The analysis shows that VIIRS RSR was
well measured in the pre-launch test program for all bands, although the measurement noise floor is high on
the thermal imager band I5. The RSR contain expected detector to detector variation resulting from the
VIIRS non-telecentric optical design, and out-of-band features are present in some bands; non-compliances
on the integrated out-of-band spectral performance metric are noted in M15 and M16A,B bands and also for
several VisNIR bands, though the VisNIR non-compliances were expected due to known scattering in the
VisNIR integrated filter assembly. The Government Team "best" RSR have been released into the public
domain for use by the science community in preparation for the post-launch era of VIIRS F1.