The JPSS-3 VIIRS sensor has completed its pre-launch test program including measurements for characterizing the VIIRS relative spectral response (RSR) in support of the Sensor and Environmental Data Records (SDR and EDR, resp.) that will be generated from VIIRS on-orbit observations. Government team subject matter experts of the VIIRS DAWG have analyzed the VIIRS spectral measurements and produced the VIIRS spectral characterization, in the form of band-average and supporting detector level RSR for each VIIRS band. The characterization is based upon the analysis of independent SpMA dual monochromator (all bands) and GSFC GLAMR laser system (reflectance bands only) spectral measurements. The SpMA and GLAMR measurements for reflectance bands (DNB LGS and MGS, I1-I3, M1-M11) were combined to produce a “fused” RSR. For emissive bands (I4, I5, M12-M16), the SpMA measurements provide the characterization. The effort has led to the VIIRS Version 2 RSR release, the official at-launch RSR characterization for the JPSS-3 VIIRS mission. The JPSS-3 RSR are a close match to those of JPSS-2. An assessment on compliance with spectral performance metrics finds that VIIRS band-average RSR are compliant on nearly all metrics, with only a single minor exception. The Version 2 RSR release is available under EAR99 restrictions to the science community on the restricted access NASA Sharepoint.
The Joint Polar Satellite System 4 (JPSS-4) is the follow-on for the Suomi-National Polar-orbiting Partnership (S-NPP) and Joint Polar Satellite Systems 1-3 (JPSS-1, -2 and -3) missions. A primary sensor on both JPSS and S-NPP spacecrafts is the Visible-Infrared Imaging Radiometer Suite (VIIRS) that provides valuable weather and climate products to the user community. VIIRS covers the Reflective Solar Band (RSB) and Thermal Emissive Band (TEB) spectral regions and contains a Day Night Band (DNB) that uses Lunar illumination at night. VIIRS provides top-of-atmosphere radiance, reflectance, and brightness temperature within the Sensor Data Records (SDRs) that are used in sea surface temperature, cloud characterization, land surface properties and ocean color/chlorophyll Environmental Data Record (EDR) products. The SDR calibration is performed using unpolarized sources such as a Solar Diffuser (SD) for the RSBs or an On-Board Calibrator BlackBody (OBCBB) for the TEBs. Earth scenes with polarizing properties will create radiometric bias errors within the SDRs based on how sensitive VIIRS is to polarized illumination and must be corrected in some EDR algorithms. This paper will discuss the JPSS-4 VIIRS polarization characterization methodology, polarization sensitivity results and compare its performance to its predecessors S-NPP and JPSS-1 through -3 VIIRS.
KEYWORDS: Sensors, Calibration, Staring arrays, Black bodies, Sensor performance, Mirrors, Mid-IR, Long wavelength infrared, Signal to noise ratio, Satellites
The Joint Polar Satellite System 3 (JPSS-3) is the follow-on to the Suomi-National Polar-orbiting Partnership (S-NPP), National Oceanic and Atmospheric Administration 20 (NOAA-20) and JPSS-2 satellites. A primary sensor on the S-NPP, NOAA-20 and JPSS satellites, the Visible-Infrared Imaging Radiometer Suite (VIIRS) has 22 bands covering a spectral range of 0.412-12.0 µmwith spatial resolutions of 742mand 371m for the moderate and imaging bands, respectively. VIIRS provides radiometrically calibrated Sensor Data Records (SDRs) using a combination of pre -launch characterization and on-orbit calibration sources, such as the Solar Diffuser (SD) for the Reflective Solar Bands (RSBs) and an On-Board Calibrator BlackBody (OBCBB) for the Thermal Emissive Bands (TEBs), for gain correction. Each VIIRS sensor build goes through extensive pre-launch characterization at vendor’s testing facility. This includes ambient, vibration, electro-magnetic interference and thermal vacuum (TVAC) environments. Each test environment is used to characterize different performance parameters for sensor functionality and on-orbit applications. This paper will focus on the JPSS-3 VIIRS pre-launch TEB calibration measured during the sensor level TVAC testing in late 2020. This will include the dynamic range, noise equivalent delta temperature, gain characterization and radiometric retrievals as well as a brief comparison with heritage VIIRS sensor TVAC results.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a primary sensor on-board the Suomi-National Polar-orbiting Partnership (S-NPP) and National Oceanic and Atmospheric Administration 20 (NOAA-20) spacecrafts, launched in October 2011 and November 2017, respectively. VIIRS has 22 bands: 7 thermal emissive bands (TEBs), 14 reflective solar bands (RSBs) and a Day Night Band (DNB). Both the RSBs and TEBs use a combination of pre-launch and on-orbit calibration information to provide accurate radiance, reflectance, and brightness temperature Sensor Data Records (SDRs). An on-orbit comparison of the S-NPP and NOAA-20 RSB SDR radiances, using ground calibration sites and vicarious methods such as deep convective clouds, show that there is a ~2% bias between the two sensors for all the reflective solar bands. Additionally, the M5 (0.672 μm) and M7 (0.865 μm) bands of Suomi NPP VIIRS have larger biases. An investigation of each sensor’s pre-launch and on-orbit calibrations was performed to ascertain the root cause of the sensor-to-sensor bias. This paper will discuss the VIIRS methodologies for both pre-launch and on-orbit calibration and how they affect the SDR product performance, as well as the most likely cause for the bias . In particular, the characterization of the reflectance of the Solar Diffuser and its reflectance variation versus view geometry was performed with different methodologies for S-NPP and NOAA-20 VIIRS. It is anticipated that J2, J3 and J4 VIIRS sensors will behave more similarly to NOAA-20 than S-NPP VIIRS due to the methodology for the SD characterization being consistent with NOAA-20.
The Joint Polar-orbiting Satellite System (JPSS)-3 Visible Infrared Imaging Radiometer Suite (VIIRS) has completed a large portion of its ground test program. The VIIRS series includes two sensors successfully operating on-orbit onboard the Suomi National Polar-orbiting Partnership (SNPP) and JPSS-1 satellites and a third sensor, currently integrated into the JPSS-2 satellite, is undergoing observatory level testing. VIIRS was designed to take high quality measurements of the Earths surface from low Earth orbit which are (or will be) used to generate a large set of environmental data products important in science. To ensure that the VIIRS instruments generate these high quality measurements once on orbit, each sensor undergoes an extensive ground test program at the component, sensor, and observatory levels. One of the important aspects of the instrument performance that needs to be characterized prior to launch is the response versus scan angle (RVS). This is the scan angle dependent change in reflectance of the rotating optics. On VIIRS, the only component of the rotating optics for which the angle of incidence changes with scan angle is the half angle mirror (HAM). The RVS was characterized for all bands, including reflective and thermal channels; results indicate that the sensor is behaving within expectations. Uncertainty estimates and atmospheric corrections for water vapor were also included in the analysis. Characterization of the RVS is critical to the retrieval of the TOA radiance and hence to ensure that the sensor performs with sufficient fidelity to provide the level of data quality that the science community demands. This work focuses on the performance of the JPSS-3 VIIRS RVS derived from instrument level ground testing, by the independent government team and compares that performance to previous builds.
The Joint Polar Satellite System 3 (JPSS-3) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is the fourth in a series (S-NPP VIIRS launched in October 2011, JPSS-1 VIIRS launched in November 2017, and JPSS-2 VIIRS currently undergoing spacecraft integration) of highly advanced polar-orbiting environmental satellites. JPSS- 3 VIIRS underwent a comprehensive sensor-level Thermal Vacuum (TV) testing at the Raytheon Technologies El Segundo facility in the fall of 2020. While the test program provided characterization for many spatial, spectral, and radiometric aspects of the VIIRS sensor performance, this paper focuses on the radiometric performance of the 14 reflective solar bands (RSB) that cover the wavelength range from 0.41 to 2.3 μm. Key calibration parameters, such as the instrument gain, signal-to-noise ratio (SNR), dynamic range and radiometric uniformity, were derived in a TV environment for both the primary and redundant electronics at three instrument temperature plateaus: cold, nominal, and hot. This paper shows that all the JPSS-3 VIIRS RSB detectors have been well characterized, with the key performance metrics being comparable to those of the previous VIIRS instruments. Comparison of radiometric performance to sensor requirements, as well as a summary of key sensor testing and performance issues, will also be presented.
KEYWORDS: Tungsten, Sensors, Ceramics, Mirrors, Absorption, Camera shutters, Signal to noise ratio, Long wavelength infrared, Optical filtering, Reflectivity
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 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.
The Joint Polar Satellite System 2 (JPSS-2) is the follow-on for the Suomi-National Polar-orbiting Partnership (S-NPP) and JPSS-1 missions. These spacecrafts provide critical weather and global climate products to the user community. A primary sensor on both JPSS and S-NPP is the Visible-Infrared Imaging Radiometer Suite (VIIRS) with Earth observations covering the Reflective Solar Band (RSB), Thermal Emissive Band (TEB) and Day Night Band (DNB) spectral regions. The VIIRS Sensor Data Records (SDRs) contain the calibrated Earth observations that are used to generate numerous Environmental Data Record (EDR) products such as Ocean Color/Chlorophyll (OCC), Global Land Cover, Aerosol and Land/Sea Surface Temperature (LST/SST). This SDR calibration is performed using unpolarized sources such as the Solar Diffuser (SD) for the RSBs and an On-Board Calibrator BlackBody (OBCBB) for the TEBs. Therefore, polarized Earth scenes will have radiometric bias errors within the SDRs based on how sensitive VIIRS is to polarized illumination and is corrected in some EDR algorithms. In addition to VIIRS polarization characterization methodology, this paper will discuss the JPSS-2 polarization sensitivity results and compare its performance to its predecessors S-NPP and JPSS-1 VIIRS. Optical modifications to the JPSS-2 VIIRS sensor to address heritage polarization sensitivity issues will be discussed.
KEYWORDS: Calibration, Sensors, Infrared radiation, Black bodies, Temperature metrology, Reflectivity, Long wavelength infrared, Thermal modeling, Error analysis, Space operations
The National Oceanic and Atmospheric Administration 20 (NOAA-20) operational satellite, also known as the Joint Polar Satellite System 1 (JPSS-1), is the follow-on to the Suomi-National Polar-orbiting Partnership (S-NPP) with launch dates of November 2017 and October 2011, respectively. S-NPP and NOAA-20 provide critical weather and global climate products to the user community. The Visible-Infrared Imaging Radiometer Suite (VIIRS), a primary sensor on both SNPP and NOAA-20, has 22 bands covering a spectral range of 0.412-12.0μm with spatial resolutions of 750m and 375m for moderate and imaging bands, respectively. VIIRS provides calibrated Earth observations within the Sensor Data Records (SDRs) using on-orbit calibration sources such as the Solar Diffuser (SD) for the Reflective Solar Bands (RSBs) and an On-Board Calibrator BlackBody (OBCBB) for the Thermal Emissive Bands (TEBs), combined with pre-launch characterization information. Both the on-orbit calibration sources and pre-launch measurements contain calibration errors that propagate into the SDR radiance retrievals and degrade the performance of the Environmental Data Records (EDRs). This paper will focus on the TEB SDR calibration products and investigate the sources of the on-orbit calibration errors observed. This includes looking at gain drifts during the OBCBB warm-up and cool-down, along-scan temperature biases, and thermal model errors used in the estimation of the sensor’s background thermal emission. The pre-launch errors from the Response Versus Scan angle (RVS), calibration coefficients, and Ground Source Equipment (GSE) will also be included in the discussion. Finally, this paper will compare the differences in calibration errors between the S-NPP and NOAA-20 sensors and how they impact the SDR products in unique ways.
KEYWORDS: Calibration, Sensors, Signal to noise ratio, Space operations, Reflectivity, Short wave infrared radiation, Seaborgium, Lamps, Temperature metrology, Attenuators
The Joint Polar Satellite System 2 (JPSS-2) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is the third in a series (S-NPP VIIRS launched in October 2011 and JPSS-1 VIIRS in November 2017) of highly advanced polar-orbiting environmental satellites. JPSS-2 VIIRS underwent a comprehensive sensor-level Thermal Vacuum (TV) testing at the Raytheon's El Segundo facility in the summer of 2017. While the test program provided characterization for many spatial, spectral, and radiometric aspects of the VIIRS sensor performance, this paper focuses on the radiometric performance of the 14 reflective solar bands (RSB) that cover the wavelength range from 0.41 to 2.3 μm. Key calibration parameters, such as the instrument gain, signal- to-noise ratio (SNR), dynamic range and radiometric uniformity, were derived in TV environment for both the primary and redundant electronics at three instrument temperature plateaus: cold, nominal, and hot. This paper shows that all the JPSS-2 VIIRS RSB detectors have been well characterized, with the key performance metrics comparable to those in the prelaunch characterization of the previous two VIIRS instruments. Comparison of radiometric performance to sensor requirements as well as a summary of key sensor testing and performance issues will be presented.
The Joint Polar Satellite System 1 (JPSS-1) is the follow on mission to the Suomi-National Polar-orbiting Partnership (SNPP) and provides critical weather and global climate products to the user community. A primary sensor on both JPSS-1 and S-NPP is the Visible-Infrared Imaging Radiometer Suite (VIIRS) with the Reflective Solar Band (RSB), Thermal Emissive Band (TEB) and Day Night Band (DNB) imagery providing a diverse spectral range of Earth observations. These VIIRS observation are radiometrically calibrated within the Sensor Data Records (SDRs) for use in Environmental Data Record (EDR) products such as Ocean Color/Chlorophyll (OCC) and Sea Surface Temperature (SST). Spectrally the VIIRS sensor can be broken down into 4 groups: the Visible Near Infra-Red (VNIR), Short-Wave Infra-Red (SWIR), Mid- Wave Infra-Red (MWIR) and Long-Wave Infra-Red (LWIR). The SWIR spectral bands on JPSS-1 VIIRS have a nonlinear response at low light levels affecting the calibration quality where Earth scenes are dark (like oceans). This anomalous behavior was not present on S-NPP VIIRS and will be a unique feature of the JPSS-1 VIIRS sensor. This paper will show the behavior of the SWIR response non-linearity on JPSS-1 VIIRS and potential mitigation approaches to limit its impact on the SDR and EDR products.
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 polarization sensitivity of the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) measured pre-launch using a broadband source was observed to be larger than expected for many reflective bands. Ray trace modeling predicted that the observed polarization sensitivity was the result of larger diattenuation at the edges of the focal plane filter spectral bandpass. Additional ground measurements were performed using a monochromatic source (the NIST T-SIRCUS) to input linearly polarized light at a number of wavelengths across the bandpass of two VIIRS spectral bands and two scan angles. This work describes the data processing, analysis, and results derived from the T-SIRCUS measurements, comparing them with broadband measurements. Results have shown that the observed degree of linear polarization, when weighted by the sensor’s spectral response function, is generally larger on the edges and smaller in the center of the spectral bandpass, as predicted. However, phase angle changes in the center of the bandpass differ between model and measurement. Integration of the monochromatic polarization sensitivity over wavelength produced results consistent with the broadband source measurements, for all cases considered.
Recent pre-launch measurements performed on the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) using the NIST T-SIRCUS monochromatic source have provided wavelength dependent polarization sensitivity for select spectral bands and viewing conditions. Measurements were made at a number of input linear polarization states (twelve in total) and initially at thirteen wavelengths across the bandpass (later expanded to seventeen for some cases). Using the source radiance information collected by an external monitor, a spectral responsivity function was constructed for each input linear polarization state. Additionally, an unpolarized spectral responsivity function was derived from these polarized measurements. An investigation of how the centroid, bandwidth, and detector responsivity vary with polarization state was weighted by two model input spectra to simulate both ground measurements as well as expected on-orbit conditions. These measurements will enhance our understanding of VIIRS polarization sensitivity, improve the design for future flight models, and provide valuable data to enhance product quality in the post-launch phase.
KEYWORDS: Sensors, Tungsten, Ceramics, Signal detection, Signal to noise ratio, Optical filters, Long wavelength infrared, Absorption, Optical filtering, Calibration
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 polarization sensitivity of the Visible/NearIR (VISNIR) bands in the Joint Polar Satellite Sensor 1 (J1) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument was measured using a broadband source. While polarization sensitivity for bands M5-M7, I1, and I2 was less than 2.5 %, the maximum polarization sensitivity for bands M1, M2, M3, and M4 was measured to be 6.4 %, 4.4 %, 3.1 %, and 4.3 %, respectively with a polarization characterization uncertainty of less than 0.38%. A detailed polarization model indicated that the large polarization sensitivity observed in the M1 to M4 bands is mainly due to the large polarization sensitivity introduced at the leading and trailing edges of the newly manufactured VISNIR bandpass focal plane filters installed in front of the VISNIR detectors. This was confirmed by polarization measurements of bands M1 and M4 bands using monochromatic light. Discussed are the activities leading up to and including the two polarization tests, some discussion of the polarization model and the model results, the role of the focal plane filters, the polarization testing of the Aft-Optics-Assembly, the testing of the polarizers at the National Aeronautics and Space Administration’s (NASA) Goddard center and at the National Institute of Science and Technology (NIST) facility and the use of NIST’s Traveling Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (T-SIRCUS) for polarization testing and associated analyses and results.
A primary sensor on-board the Suomi-National Polar-orbiting Partnership (SNPP) spacecraft, the Visible Infrared Imaging Radiometer Suite (VIIRS) has 22 bands: 7 thermal emissive bands (TEBs), 14 reflective solar bands (RSBs) and a Day Night Band (DNB). The RSBs cover the spectral wavelengths between 0.412 to 2.25 μm and have three (I1-I3) 371m and eleven (M1-M11) 742m spatial resolution bands. A VIIRS Key Performance Parameter (KPP) is the Ocean Color/Chlorophyll (OCC) which uses moderate bands M1 (0.412μm) through M7’s (0.865 μm) calibrated Science Data Records (SDRs). The RSB SDRs rely on prelaunch calibration coefficients which use a quadratic algorithm to convert the detector’s response to calibrated radiance. This paper will evaluate the performance of these prelaunch calibration coefficients using SDR comparisons between bands with the same spectral characteristics: I2 with M7 (0.865 μm) and I3 with M10 (1.610 μm). Changes to the prelaunch calibration coefficient’s offset term c0 to improve the SDR’s performance at low radiance levels will also be discussed.
KEYWORDS: Calibration, Sensors, Infrared radiation, Reflectivity, Thermography, Space operations, Long wavelength infrared, Infrared sensors, Black bodies, Temperature metrology
The Visible Infrared Imager Radiometer Suite (VIIRS), a primary sensor on-board the Suomi-National Polar-orbiting Partnership (SNPP) spacecraft, was launched October 28, 2011. It has 22 bands: 7 thermal emissive bands (TEBs), 14 reflective solar bands (RSBs) and a Day Night Band (DNB). The TEBs cover the spectral wavelengths between 3.7 to 12 μm and have two 371 m and five 742 m spatial resolution bands. A VIIRS Key Performance Parameter (KPP) is the sea surface temperature (SST) which uses bands M12 (3.7 μm), M15 (10.8 μm) and M16’s (12.0 μm) calibrated Science Data Records (SDRs). The TEB SDRs rely on pre-launch calibration coefficients used in a quadratic algorithm to convert the detector’s response to calibrated radiance. This paper will evaluate the performance of these prelaunch calibration coefficients using vicarious calibration information from the Cross-track Infrared Sounder (CrIS) also onboard the SNPP spacecraft and the Infrared Atmospheric Sounding Interferometer (IASI) on-board the Meteorological Operational (MetOp) satellite. Changes to the pre-launch calibration coefficients’ offset term c0 to improve the SDR’s performance at cold scene temperatures will also be discussed.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) is an instrument on-board the Suomi National Polar-orbiting
Partnership (NPP) spacecraft, which launched on October 28, 2011. VIIRS performs measurements in 14 reflective
solar bands (RSBs) spanning wavelengths from 412 nm to 2.25 um, which are calibrated by using solar radiance
reflected from a Solar Diffuser (SD). The SD reflectance degrades over time, and a Solar Diffuser Stability Monitor
(SDSM) is used to track the changes. The ratio between the calculated solar radiance reflected from the SD and the
VIIRS measurement of this radiance using the pre-launch calibration coefficients is known as the “F factor.” The F
factor is applied in the ground processing as a scale correction to the pre-launch calibration coefficients used to generate
the calibrated radiances and reflectances comprising the Sensor Data Records (SDRs). The F factor is trended over time
to track instrument response degradation. The equation for calculating expected solar radiance, and the coefficients used
to convert the raw digital numbers measured by the detectors into radiance and reflectance values, are based on
parameters stored in various Look-Up Tables (LUTs). This paper will discuss on-orbit RSB calibration for VIIRS, along
with a description of the processing methodology, which includes operational LUT updates based on off-line
calculations of F factor trending behavior.
The Suomi – NPP Visible Infrared Imager Radiometer Suite (VIIRS) reflective bands are calibrated on-orbit
via reference to regular solar observations through a solar attenuation screen (SAS) and diffusely reflected off a
Spectralon ® panel. The degradation of the Spectralon panel BRDF due to UV exposure is tracked via a ratioing
radiometer (SDSM) which compares near simultaneous observations of the panel with direct observations of the
sun (through a separate attenuation screen). On-orbit, the vignetting functions of both attenuation screens are
most easily measured when the satellite performs a series of yaw maneuvers over a short period of time (thereby
covering the yearly angular variation of solar observations in a couple of days). Because the SAS is fixed, only the
product of the screen transmission and the panel BRDF was measured. Moreover, this product was measured
by both VIIRS detectors as well as the SDSM detectors (albeit at different reflectance angles off the Spectralon
panel). The SDSM screen is also fixed; in this case, the screen transmission was measured directly. Corrections
for instrument drift and degradation, solar geometry, and spectral effects were taken into consideration. The
resulting vignetting functions were then compared to the pre-launch measurements as well as models based on
screen geometry.
On October 28th, 2011, the Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched on-board the Suomi
National Polar-orbiting Partnership (NPP) spacecraft. The instrument has 22 spectral bands: 14 reflective solar
bands (RSB), 7 thermal emissive bands (TEB), and a Day Night Band (DNB). The DNB is a panchromatic, solar
reflective band that provides visible through near infrared (IR) imagery of earth scenes with radiances spanning 7
orders of magnitude. In order to function over this large dynamic range, the DNB employs a focal plane array (FPA)
consisting of three gain stages: the low gain stage (LGS), the medium gain stage (MGS), and the high gain stage
(HGS). The final product generated from a DNB raw data record (RDR) is a radiance sensor data record (SDR).
Generation of the SDR requires accurate knowledge of the dark offsets and gain coefficients for each DNB stage.
These are measured on-orbit and stored in lookup tables (LUT) that are used during ground processing. This paper
will discuss the details of the offset and gain measurement, data analysis methodologies, the operational LUT update
process, and results to date including a first look at trending of these parameters over the early life of the instrument.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched onboard the Suomi National Polar-orbiting
Partnership (NPP) spacecraft on October 28, 2011. Among the bands on VIIRS are 14 reflective solar bands (RSBs).
The RSBs are calibrated using the sun as a source, after attenuation and reflection of sunlight from a Solar Diffuser (SD).
The reflectance of the SD is known to degrade over time, particularly at the blue end of the visible spectrum. VIIRS
incorporates a separate instrument, a Solar Diffuser Stability Monitor (SDSM), in order to measure and trend the SD
Bidirectional Reflectance Distribution Function BRDF changes over time. Inadequate knowledge of the SDSM screen
transmission as a function of solar geometry and SDSM detector dependent modulation effects require a unique
processing methodology to eliminate unphysical artifacts from the SD BRDF trending. The unique methodology is used
to generate periodic updates to operational Look-up Tables (LUTs) used by the Sensor Data Record (SDR) operational
code to maintain the calibration of the RSBs. This paper will discuss on-orbit SD BRDF behavior along with the
processing methodology used to generate RSB LUT updates incorporating the trended SD BRDF behavior.
KEYWORDS: Calibration, Sensors, Temperature metrology, Black bodies, Reflectivity, Detection and tracking algorithms, Space operations, Atmospheric sensing, Sensor performance, Staring arrays
The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched October 28, 2011 on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft as a primary sensor. It has 22 bands: 14 reflective solar bands (RSBs), 7 thermal emissive bands (TEBs) and a Day Night Band (DNB). VIIRS TEB on-orbit calibration uses a quadratic algorithm with its calibration coefficients derived from pre-launch measurements and an on-board calibration blackbody (OBC BB) to provide scan-to-scan gain drift compensation. This paper will discuss the calibration methodology, OBC BB performance and stability, detector signal-to-noise and radiometric performance.
KEYWORDS: Sensors, Calibration, Signal to noise ratio, MODIS, Reflectivity, Mirrors, Ultraviolet radiation, Space operations, Bidirectional reflectance transmission function, Data modeling
The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a key instrument on-board the Suomi National Polarorbiting
Partnership (NPP) spacecraft that was launched on October 28th 2011. VIIRS was designed to provide
moderate and imaging resolution of the planet Earth twice daily. It is a wide-swath (3,040 km) cross-track scanning
radiometer with spatial resolutions of 375 m and 750 m at nadir for imaging and moderate bands, respectively. It has
22 spectral bands covering the spectrum between 0.4 μm and 12.5 μm, including 14 reflective solar bands (RSB), 7
thermal emissive bands (TEB), and 1 day-night band (DNB). VIIRS observations are used to generate 22
environmental data record (EDRs). This paper will briefly describe NPP VIIRS calibration strategies performed by
the independent government team, for the initial on-orbit Intensive Calibration and Validation (ICV) activities. In
addition, this paper will provide an early assessment of the sensor on-orbit radiometric performance, such as the
sensor signal to noise ratios (SNRs), dual gain transition verification, dynamic range and linearity, reflective bands
calibration based on the solar diffuser (SD) and solar diffuser stability monitor (SDSM), emissive bands calibration
based on the on-board blackbody calibration (OBC), and cross-comparison with MODIS. A comprehensive set of
performance metrics generated during the pre-launch testing program will be compared to VIIRS early on-orbit
performance, and a plan for future cal/val activities and performance enhancements will be presented.
The Suomi National Polar-orbiting Partnership (NPP) satellite was launched on Oct. 28, 2011, and began the
commissioning phase of several of its instruments shortly thereafter. One of these instruments, VIIRS, was found to
exhibit a gradual but persistent decrease in the optical throughput of several bands, with the near-infrared bands being
more affected than those in the visible. The rate of degradation quickly increased upon opening of the nadir door that
permits the VIIRS telescope to view the earth. Simultaneously, a second instrument on NPP, the Solar Diffuser Stability
Monitor (SDSM), was experiencing a similar decrease in response, leading the investigation team to suspect that the
cause must be the result of some common contamination process. This paper will discuss a series of experiments that
were performed to demonstrate that the VIIRS and SDSM response changes were due to separate causes, and which
enabled the team to conclude that the VIIRS sensor degradation was the result of ultraviolet light exposure of the
rotating telescope assembly. The root cause investigation of the telescope degradation will be addressed in a separate
paper.
KEYWORDS: Space operations, Sensors, Aerospace engineering, Quality measurement, Polarization, Aerosols, Infrared radiation, Long wavelength infrared, Clouds, Signal to noise ratio
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.
Verification of the Visible Infrared Imager Radiometer Suite (VIIRS) End-to-End (E2E) sensor calibration is
highly recommended before launch, to identify any anomalies and to improve our understanding of the sensor onorbit
calibration performance. E2E testing of the Reflective Solar Bands (RSB) calibration cycle was performed
pre-launch for the VIIRS Flight 1 (F1) sensor at the Ball Aerospace facility in Boulder CO in March 2010.
VIIRS reflective band calibration cycle is very similar to heritage sensor MODIS in that solar illumination, via a
diffuser, is used to correct for temporal variations in the instrument responsivity. Monochromatic light from the
NIST T-SIRCUS (Traveling Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources)
was used to illuminate both the Earth View (EV), via an integrating sphere, and the Solar Diffuser (SD) view,
through a collimator. The collimator illumination was cycled through a series of angles intended to simulate the
range of possible angles for which solar radiation will be incident on the solar attenuation screen on-orbit. Ideally,
the measured instrument responsivity (defined here as the ratio of the detector response to the at-sensor radiance)
should be the same whether the EV or SD view is illuminated. The ratio of the measured responsivities was
determined at each collimator angle and wavelength. In addition, the Solar Diffuser Stability Monitor (SDSM), a
ratioing radiometer designed to track the temporal variation in the SD Bidirectional Reflectance Factor (BRF) by
direct comparison to solar radiation, was illuminated by the collimator. The measured SDSM ratio was compared
to the predicted ratio. An uncertainty analysis was also performed on both the SD and SDSM calibrations.
The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor carried on the
NPOESS (National Polar-orbiting Operational Environmental Satellite System) Preparatory
Project (NPP) mission [1] (http://jointmission.gsfc.nasa.gov/viirs.html), and is
scheduled to launch in October 2011. VIIRS sensor design draws on heritage instruments
including AVHRR, OLS, MODIS, and SeaWiFS. It has on-board calibration components
including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the
reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB),
and a space view (SV) port for background subtraction. These on-board calibrators are
located at fixed scan angles. The VIIRS response versus scan angle (RVS) was
characterized prelaunch in lab ambient conditions and will be used on-orbit to
characterize the response for all scan angles relative to the calibrator scan angle (SD
for RSB and blackbody for TEB). Since the RVS is vitally important to the quality of
calibrated radiance products, several independent studies were performed and their
results were compared and validated. This document provides RVS results from three
groups: the NPP Instrument Calibration Support Team (NICST), Raytheon, and the Aerospace
Corporation. A comparison of the RVS results obtained using a 2nd order polynomial fit to
measurement data is conducted for each band, detector, and half angle mirror (HAM) side.
The associated RVS fitting residuals are examined and compared with the relative
differences in RVS found between independent studies. Results show that the agreement is
within 0.1% and comparable with fitting residuals for all bands except for RSB band M9,
where a difference of 0.2% was observed. Band M9 is highly sensitive to the atmospheric
water vapor variations during the sensor ambient testing at Raytheon, and its correction might be a contributor to the observed RVS uncertainty differences. In general, NICST
results have shown slightly larger RSB RVS uncertainties but still well within the 0.3%
total uncertainty allowed for the RVS characterization defined in the Performance
Verification Plan.
KEYWORDS: Sensors, Signal to noise ratio, MODIS, Camera shutters, Aerospace engineering, Optical filters, Absorption, Optical design, Polarization, Long wavelength infrared
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.
The Modulation Transfer Function (MTF) is a standard measure of the spatial quality of an imaging sensor. The MTF is
calculated by a normalized Fourier Transform of a Point Spread Function (PSF), which is a two-dimensional function.
For simplicity of calculation, a one-dimensional PSF, or Line Spread Function (LSF) is utilized in the along-scan
direction. The along-scan direction LSF model is sub-divided into the component level LSFs and the proper LSF is
constructed by the design specification information. To construct the modeled LSF, a spatial convolution is performed
for the three major components: optical, detector, and integration time LSFs. The optical LSF is calculated using Zemax.
The detector LSF is modeled as a rectangular function of the nominal detector size. Similar to the detector LSF, the
integration time LSF is modeled as a rectangular function by using the sampling frequency and the integration pulse
duration time. The modeling LSF is compared with the measured LSF from a prelaunch ground calibration device, the
Integrated Alignment Collimator (IAC). Because the IAC test slit has a width of 0.1 MODIS IFOV, an extra step pulse
convolution is added to the final LSF model. The comparison results show an excellent agreement between the modeled
and measured LSFs in the spatial domain and MTFs in the frequency domain for selected reflective solar bands (RSB).
The Visible/Infrared Imager/Radiometer Suite (VIIRS) collects visible/infrared imagery and radiometric data. The
radiometric requirements are such that the instrument's polarization sensitivity must be very well understood. This paper
presents the ZEMAX and FORTRAN polarization ray trace models of the instrument's visible light path. This will include
the measured optical surface reflectance data, the band pass shapes and a comparison of the results of the two models.
The Moderate Resolution Imaging Spectroradiometer (MODIS) flight model 1 (FM-1) was launched on-board NASA's EOS Aqua spacecraft on May 04, 2002. MODIS has 20 reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μm and 16 thermal emissive bands (TEB) with wavelengths from 3.7 to 14.4μm. Typical sensor spectral characterization includes measurements of in-band (IB) and out-of-band (OOB) relative spectral responses (RSR) or spectral response functions (SRF), center wavelengths (CW) and bandwidths (BW). During MODIS instrument pre-launch calibration and characterization, these parameters were measured using a spectral measurement assembly (SpMA) by the instrument vendor. In addition to its on-orbit radiometric calibration capability, MODIS has a unique on-board calibrator, spectro-radiometric calibration assembly (SRCA) that can be used to monitor RSB on-orbit spectral performance. This paper presents an overview of MODIS spectral characterization methodologies, from pre-launch to on-orbit. It describes Aqua MODIS SRCA operational activities in spectral mode, summarizes the results from its four-years of on-orbit spectral measurements, and discusses lessons learned for future sensor design and development. The results show that on-orbit changes of Aqua MODIS RSB center wavelengths and bandwidths have been very small, typically less than 0.5nm for the CW and less than 1nm for the BW.
Twenty of the 36 MODIS spectral bands are reflective solar bands (RSB). They are calibrated on-orbit by an onboard solar diffuser (SD). For the high-gain ocean color bands (8-16), an attenuating solar diffuser screen (SDS) is used in front of the SD panel to avoid detector saturation caused by direct solar illumination of the SD. The use of the SDS, a metal plate with uniformly distributed pinholes, introduces an additional factor to the radiometric calibration uncertainty. Since a system level characterization of the SDS transmission versus SD viewing geometry was not performed pre-launch, the vignetting function (VF) for both Terra and Aqua MODIS had to be characterized on-orbit. The VF can be derived either from SD observations made with and without the SDS in place during specially planned spacecraft yaw maneuvers or by using routine SD calibration pairs (with and without the SDS) accumulated over a long period in order to cover all possible viewing geometries. In this paper we present details of the methods used to characterize the MODIS SDS VFs and examine the results derived from both spacecraft yaw maneuvers and long-term SD calibration pairs. The VF results obtained for Terra and Aqua MODIS are discussed and compared. In addition, an estimate of the calibration uncertainties introduced by the SDS is provided.
On-orbit optical sensors are the primary data source for the remote sensing community. A rigorous pre-flight characterization and calibration is a key to the success of their mission. Indeed, preliminary calibration and correction factors are determined during this process. As part of this process, prior to the launch of NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) its polarization sensitivity was measured. In this work, our goal was to simulate these measurements using computer ray tracing software. Based on that, we could evaluate the evolution of the different coatings (Mirror, Beam splitters, Anti-reflection and Band pass filters) due to degradation over time. We were able to simulate the measurements and obtained what the theoretical polarization sensitivity should be. The results were compared to the pre-launch measurements and an analysis of the whole MODIS optical system was performed in order to explain these differences. A full description of the MODIS polarization ray tracing procedure along with a discussion on the results and their implications on past, present and future work will be given.
A computer model of the MODIS attenuated (with screen down) solar calibration has been developed. Observed (visible) focal plane variations are presented and compared with modeled results. The agreement is quite good over the full range of scan mirror and solar motions. Causes for discrepancies are discussed.
The MODIS instrument relies on solar calibration to achieve the required radiometric accuracy. This solar calibration occurs as the TERRA spacecraft comes up over the North Pole. The earth underneath the spacecraft is still dark for approximately one minute and the sun is just rising over the earth's north polar regions. During this time the sun moves through about 3.3 degrees, the scan mirror rotates about 19 times and about 50 exposures (frames) are taken each time the field of view is directed to the approximate center (sweet spot) of the solar diffuser. For some of MODIS's bands the brightness of the diffuser is reduced, to prevent detector saturation, by means of a retractable pinhole screen, which produces approximately 600 pinhole images of the sun, within the field of view of any one detector. Previous attempts at creating a radiometric model of this, reduced intensity, calibration scenario produced intensity variations on the focal planes with insufficient detail to be useful. The current computational approach, gets around these limitations and is fast enough to permit simulation of the motion of the sun and the scan mirror. The results resemble the observed focal plane temporal and spatial intensity variations well enough to be useful. The computational approach is described and a comparison with observational data is presented.
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