The NOAA-21 (N-21) VIIRS has successfully operated for more than 1 year since its launch on November 10, 2022. This paper provides a comprehensive assessment of its on-orbit performance based on measurements made during its initial post-launch testing (PLT) and ensuing on-orbit calibration and characterization. Results presented in this paper include performance of its on-board calibrators (OBC), detector noise characteristics, on-orbit changes in its spectral band responses and spatial performance in terms of band-to-band registrations (BBR). In general, the N-21 VIIRS overall performance is comparable to or better than its predecessor S-NPP and N-20 VIIRS, with an exception of large changes in its SWIR band responses at mission beginning. On-orbit assessment also shows a more effective stray light reduction in N-21 day and night band (DNB).

Launched on November 10, 2022, the NOAA-21 (N-21) VIIRS has successfully completed its initial post-launch testing (PLT) and intensive calibration and validation (ICV) activities. It is now operated in its nominal configuration and characterized using measurements from its on-board calibrators (OBC) and lunar observations. In this paper, we provide a brief description of N-21 VIIRS on-orbit operation and calibration activities and present results derived from its early mission performance assessments, including examples of its OBC performance, spectral band responses, as well as detector signal to noise characteristics. As shown in this paper, the overall performance of N-21 VIIRS is better than that of its predecessor currently operated on the S-NPP and comparable to the one onboard the N-20, with an exception of relatively large changes in its SWIR band responses.

The earth-observing visible infrared imaging radiometer suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite regularly calibrates its reflective solar bands (RSBs), primarily through observing an onboard sunlit solar diffuser (SD). The on-orbit change of the value of the SD bidirectional reflectance distribution function (BRDF) is quantified by a numerical factor, called the H-factor, and is determined by the onboard SD stability monitor (SDSM). Because the spectral response function of an SDSM detector spreads in wavelength, the directly measured H-factor is the true H-factor convolved with the spectral response function. To find the true H-factor, we use the traditional direct method and an innovative iterative approach to separately deconvolve the measured H-factor. Our iterative approach relies on two properties of the SDSM detector spectral response function: the central peak width is narrow enough so that the H-factor does not change much over the peak width, and the dominance of the spectral response function’s integral with respect to the wavelength over the width. The iterative approach is more accurate, of a smaller noise impact, much more flexible in terms of interpolation and extrapolation of functional values, and faster. We have used deconvolved H-factors to calibrate the NASA SNPP VIIRS RSB Collections 1 and 2 Level-1B products.

The NOAA-20 (N20) satellite was launched on November 18, 2017 carrying the second Visible Infrared Imaging Radiometer Suite (VIIRS) instrument. Immediately following the launch, the VIIRS passed a series of intensive calibration and validation tests, after which regular calibration and operation activities have continued successfully for more than three years. The production of NASA Collection 2 Level 1B (C2 L1B) for N20 VIIRS began in summer 2019. In this article, we evaluate the early mission performance of the N20 VIIRS reflective solar bands (RSB) covering the first three full years of operation. The calibrated RSB gains are calculated primarily from the onboard solar diffuser (SD) and used in generating the C2 L1B reflectance and radiance products. We also show the on-orbit performance of the instrument noise, signal-to-noise ratio (SNR), and a reflectance uncertainty assessment. Comparisons are made to the first three years of operation of the first VIIRS instrument, aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. We evaluate the long-term stability of the calibrated N20 RSB reflectance product by looking at the long-term trends of lunar observations and data from the pseudo-invariant Libya 4 desert site. The N20 RSB have had excellent early mission performance, with changes in the gain of less than 0.5% in the first three years across all detectors, stable L1B reflectance, and very stable values of detector SNR and reflectance uncertainty.

Visible Infrared Imaging Radiometer Suite (VIIRS) radiometrically calibrates its reflective solar bands (RSBs) primarily through a sunlit onboard solar diffuser (SD). The sunlit SD provides a known radiance under the condition that the absolute product of the SD screen transmittance and the bidirectional reflectance distribution function (BRDF) along the SD-to-telescope direction is accurately known. The BRDF changes due to solar exposure. The change, referred to as the H-factor, is monitored by the onboard SD stability monitor (SDSM). The accuracy of the retrieved H-factor propagates to the retrieved F-factor which corrects the scene spectral radiance. High accuracy of the retrieved H-factor relies on high accuracies in the SDSM screen relative effective transmittance and the relative product of the SD screen effective transmittance and the BRDF at the mission start, and a high SDSM detector signal-to-noise ratio (SNR). This article briefly reviews the algorithms used for the NOAA-20 (N20) VIIRS RSB on-orbit radiometric calibration. Additionally, we show the performance of the N20 VIIRS SDSM, giving the SDSM detector SNRs and the SDSM detector gain temporal changes. We develop a model for the SNRs. The model shows that the decreased SNRs in time are due to the detector gain decreases. We also show the N20 VIIRS SD on-orbit performance, measured by the retrieved H-factor and the estimated standard deviation of its error. The H-factor for the telescope view is obtained from the H-factor for the SDSM view, multiplied by an H-factor angular dependence term. We use an innovative method to determine the angular dependence, using the dependence obtained for the Suomi National Polar-orbiting Partnership (SNPP) VIIRS.

The Earth-observing Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite regularly performs on-orbit radiometric calibration of its reflective solar bands (RSBs), primarily through observations of an onboard sunlit solar diffuser (SD). The on-orbit change of the SD bidirectional reflectance distribution function (BRDF) value, quantified by a numerical factor called the H-factor, is determined by the onboard SD stability monitor. Our previous study showed that the H-factor is solar angle- and view direction-dependent. In this study, we determine the dependence of the H-factor on the detector SD view footprint location. We fit an empirical model to the NASA Collection 1 SNPP VIIRS Level 1B (L1B) spectral reflectance difference across the detectors in an RSB over uniform Earth scenes of the Libya 4 desert and deep convective clouds (DCCs). We apply the model predicted SD-positional-dependent H-factor to calibrate the RSBs. Under this new calibration scheme, the original unreal striping is removed from the homogeneous Libya 4 desert and the DCC images, as well as the original unreal striping from the Dunhuang desert image. The SD-positional-dependent H-factor has been used to calculate the SNPP VIIRS RSB radiometric correction factor for the NASA Collection 2.0 SNPP VIIRS L1B products.

The NOAA-20 (N-20) VIIRS has successfully operated for more than two years since its launch in November 2017. Shortly after completing its initial instrument check-outs and post-launch testing (PLT) activities, the N-20 VIIRS sensor data records (SDR) achieved the beta, provisional, and validated maturity status in January, February, and April 2018, respectively. In this paper, we briefly describe the instrument on-orbit operation and calibration activities, provide an overall assessment of its on-orbit performance, and discuss the methodologies developed to maintain and improve sensor calibration and data quality. As illustrated in this paper, the N-20 VIIRS continues to perform with excellent stability, allowing high-quality environmental data records (EDR) to be generated from its well-calibrated SDR.

Launched in November 2017, the NOAA-20 (N-20) VIIRS has successfully completed more than 1.5 years of on-orbit operations. In addition to initial post-launch check-outs followed by a series of intensive calibration and validation activities, the instrument performed a mid-mission outgassing in March 2018 to remove the ice buildup on the dewar window of the long-wave infrared (LWIR) focal plane assembly that had caused gradual degradation of detector responses (gains) of several LWIR spectral bands. Since then, the instrument has been in nominal operations. This paper provides an update of N-20 VIIRS on-orbit calibration activities and performance assessments using data from its on-board calibrators (OBCs) and regularly scheduled lunar observations, and discusses issues identified and efforts made to improve the calibration and data quality. Also briefly described in this paper are remaining challenges in terms of calibration consistency between NOAA-20 and S-NPP VIIRS.

Since launch in November 2018, the VIIRS on-board the NOAA-20 (or JPSS-1) satellite has completed its initial intensive on-orbit check-outs and several key calibration and validation activities scheduled to help evaluate sensor at launch performance. This paper provides a brief overview of NOAA-20 VIIRS on-orbit operation and calibration activities, presents early results derived from its on-board calibrators and lunar observations, and discusses potential improvements and future effort to assure sensor data product quality.

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor was on board the Suomi National Polar-Orbiting Partnership (S-NPP) launched on 28 October 2011. The VIIRS includes a day-night band (DNB), which is panchromatic with the wavelengths from 500 nm to 900 nm. Its dynamic range covers from full sunlit scenes to lunar-illuminated images. With successful calibration after launch, DNB on-orbit performance is very well, meeting most of its specifications with some minor exceedances. In this paper, the DNB calibration uncertainty is focused on different modes, ham-side and detectors. The DNB gain coefficients, dark offsets and the solar diffuser (SD) digital-count variance are mainly considered, together with the BRDF, transmittance of pin-hole screen, RSR and H-factor uncertainties. The case of Low gain stage (LGS) is addressed. The results help quantify the uncertainty in the performance trends which better define the roles of each parameters in DNB imaginary and calibration.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite uses its 14 reflective solar bands to passively collect solar radiant energy reflected off the Earth. The Level 1 product is the geolocated and radiometrically calibrated top-of-the-atmosphere solar reflectance. The absolute radiometric uncertainty associated with this product includes contributions from the noise associated with measured detector digital counts and the radiometric calibration bias. Here, we provide a detailed algorithm for calculating the estimated standard deviation of the retrieved top-of-the-atmosphere spectral solar radiation reflectance.

In this paper the calibration methodology, data and models, and the absolute bias of HY-2A, Jason-2, and Saral/AltiKa based on the Qianliyan CAL/VAL site will be presented.

To ensure data quality, the Earth-observing Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellite regularly performs on-orbit radiometric calibration of its 22 spectral bands. The primary radiance source for the calibration of the VIIRS reflective solar bands (RSBs) is a sunlit onboard solar diffuser (SD). During the calibration process, sunlight goes through a perforated plate (the SD screen) and then strikes the SD. The sunlight, scattered off the SD of near-Lambertian property, is used for the calibration. Consequently, the spectral radiance of the scattered sunlight is proportional to the product of the SD screen transmittance and the SD bidirectional reflectance distribution function (BRDF) value at the observation direction. The BRDF value is decomposed to the product of its initial value at launch and a numerical degradation factor that quantifies the decrease from the initial value. The degradation factor is determined by an onboard SD stability monitor (SDSM). During the BRDF degradation factor determination process, the SDSM receives the SD scattered sunlight and the sunlight that goes through another perforated plate at almost the same time. The ratio of the signal strengths from the two observations is used to determine the BRDF degradation factor. Consequently, the RSB radiometric calibration requires the accurate knowledge of the product of the SD screen transmittance and the initial BRDF value as sensed by the RSB and the SDSM detectors. We use both yaw maneuver and a small portion of regular on-orbit data to determine the products.

Using an onboard sunlit solar diffuser (SD) as the primary radiance source, the visible infrared imaging radiometer suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellite regularly performs radiometric calibration of its reflective solar bands (RSBs). The SD bidirectional reflectance distribution function (BRDF) value decreases over time. A numerical degradation factor is used to quantify the degradation and is determined by an onboard SD stability monitor (SDSM), which observes the sun and the sunlit SD at almost the same time. We had shown previously that the BRDF degradation factor was angle-dependent. Consequently, due to that the SDSM and the RSB view the SD at very different angles relative to both the solar and the SD surface normal vectors, directly applying the BRDF degradation factor determined by the SDSM to the VIIRS RSB calibration can result in large systematic errors. We develop a phenomenological model to calculate the BRDF degradation factor for the RSB SD view from the degradation factor for the SDSM SD view. Using the yearly undulations observed in the VIIRS detector gains for the M1-M4 bands calculated with the SD BRDF degradation factor for the SDSM SD view and the difference between the VIIRS detector gains calculated from the SD and the lunar observations, we obtain the model parameter values and thus establish the relation between the BRDF degradation factors for the RSB and the SDSM SD view directions.

The first VIIRS instrument has successfully operated for more than 4 years on-board the Suomi-National Polar-orbiting Partnership (S-NPP) spacecraft. The sensor data records (SDR) derived from VIIRS on-orbit observations have been used to produce many environment data records (EDR), enabling a wide range of applications by the users from operational and research community. This paper provides an overview of instrument operations and its calibration activities, and presents an update of its radiometric performance, in terms of on-orbit changes in sensor spectral band responses and noise characterization. It also describes the effort made to improve sensor calibration, and the strategies developed in support of producing consistent SDR and, consequently, the EDR with improved quality.

When illuminated by the Sun, the onboard solar diffuser (SD) panel provides a known spectral radiance source to calibrate the reflective solar bands of the Visible Infrared Imaging Radiometer Suite on the Suomi-NPP satellite. The SD bidirectional reflectance distribution function (BRDF) degrades over time due to solar exposure, and this degradation is measured using the SD stability monitor (SDSM). The SDSM acts as a ratioing radiometer, comparing solar irradiance measurements off the SD panel to those from a direct Sun view. We discuss the design and operations of the SDSM, the SDSM data analysis, including improvements incorporated since launch, and present the results through 1000 days after launch. After 1000 days, the band-dependent H-factors, a quantity describing the relative degradation of the BRDF of the SD panel since launch, range from 0.716 at 412 nm to 0.989 at 926 nm. The random uncertainty of these H-factors is about 0.1%, which is confirmed by the similar standard deviation values computed from the residuals of quadratic exponential fits to the H-factor time trends. The SDSM detector gains have temperature sensitivity of up to about 0.36% per kelvin, but this does not affect the derived H-factors. An initial error in the solar vector caused a seasonal bias to the H-factors of up to 0.5%. The total exposure of the SD panel to UV light after 1000 orbits is equivalent to about 100 h of direct sunlight illumination perpendicular to the SD panel surface.

The Visible Infrared Imaging Radiometer Suite aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite performs radiometric calibration of its reflective solar bands primarily through observing a sunlit onboard solar diffuser (SD). The SD bidirectional reflectance distribution function (BRDF) degradation factor is determined by an onboard SD stability monitor (SDSM), which observes the Sun through a pinhole screen and the sunlit SD. The transmittance of the SDSM pinhole screen over a range of solar angles was determined prelaunch and used initially to determine the BRDF degradation factor. The degradation-factor-versus-time curves were found to have a number of very large unphysical undulations likely due to the inaccuracy in the prelaunch determined SDSM screen transmittance. To refine the SDSM screen transmittance, satellite yaw maneuvers were carried out. With the SDSM screen relative transmittance determined from the yaw maneuver data, the computed BRDF degradation factor curves still have large unphysical ripples, indicating that the projected solar horizontal angular step size in the yaw maneuver data is too large to resolve the transmittance at a fine angular scale. We develop a methodology to use both the yaw maneuver and a small portion of regular on-orbit data to determine the SDSM screen relative transmittance at a fine angular scale. We determine that the error standard deviation of the calculated relative transmittance ranges from 0.00030 (672 nm) to 0.00092 (926 nm). With the newly determined SDSM screen relative transmittance, the computed BRDF degradation factor behaves much more smoothly over time.

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite is an imaging radiometer, collecting data of the Earth's surface in wavelengths ranging from 0.41 to 12.5 μm. To maintain and improve data quality, the VIIRS calibrates its reflective solar bands using a sunlit onboard solar diffuser (SD) panel as the radiance source. Due to exposure to solar radiative energy and high-energy particles and perhaps on-orbit contamination, the surface property of the SD panel changes with time. An onboard SD stability monitor (SDSM) measures the change in the value of the bidirectional reflectance distribution function (BRDF) of the SD at the SDSM SD view direction. The SDSM measurements show that the BRDF value decreases over time and that the degradation is wavelength dependent. The degradation varies monotonically with the wavelength and becomes much smaller at a longer wavelength. However, the SDSM design band wavelengths (412-926 nm) are much shorter than the VIIRS short-wave infrared (SWIR) band wavelengths (1238-2257 nm). Consequently, for simplicity, for SNPP VIIRS, it has been assumed that the degradation is zero at the SWIR band wavelengths. Nevertheless, at the present time, the degradation at the shorter end of the SWIR band wavelengths may not be small enough to be negligible to satisfy the 0.1% (at least) radiometric calibration stability required by the Ocean Color products. We propose empirical models to calculate the BRDF degradation in the SWIR wavelength region.

The absolute SSH (sea surface height) biases of three satellite altimeters Jason-2, Saral/AltiKa and HY-2 were determined using our GPS buoy at the Qian Li Yan Island of China, which are 9.3cm, 1.3cm and 66.8cm, respectively. In addition, the altimetry SWH (significant wave height) were assessed using GPS retrieved SWH, which shows good agreement between the GPS buoy and satellite altimeters. The detailed method and result are described in the paper.

The on-orbit radiometric calibration of the reflective solar bands (RSBs) of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership satellite is carried out primarily through observations of a fully illuminated solar diffuser (SD) panel. Accurate knowledge of the solar spectral radiance scattered from the SD is available. The sensor aperture spectral radiance is assumed to be a quadratic polynomial function of a VIIRS detector's background-subtracted response in digital number. The coefficients of the polynomial were initially determined prelaunch. Once on orbit, we assume that these coefficients change uniformly by a common calibration factor, which is referred to as the F-factor. The known solar spectral radiance scattered from a fully illuminated SD allows for the determination of these F-factors. We describe the methodology and the associated algorithms used in the calculation of the RSB F-factors. Our results show that the F-factors change over time, with the largest change occurring at a wavelength of 862 nm (with a value of about 1.55 on day 950 after the satellite launch, relative to its value at the beginning of the launch) . In addition, we estimate the relative error standard deviations of the computed top-of-the-atmosphere reflectance at the detector pixel level. On day 950 of the mission, the relative error standard deviations are all less or equal to 0.016, except for the M11 band (band central wavelength of 2257 nm) , which has a relative error standard deviation of about 0.049 due to a very low signal-to-noise ratio.

Right after the opening of the nadir door of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership satellite, the detector gains of the near-infrared bands had decreased much faster than expected, indicating large degradation of the VIIRS optical system. To help determine the root cause and to access the potential outcome of the degradation, we developed a mathematical model based on a physical hypothesis that the observed degradation was due to the sensor Rotating Telescope Assembly (RTA) mirror surface contamination. To date, the detector gains have been consistent with a physical model of a thin contaminant layer of material on each of the four RTA reflective mirrors. The contaminated material, after exposure to solar radiation, reduces the mirror reflectance over the reflective solar band (RSB) wavelength region. We describe the mathematical model and apply the model to predict the RSB detector gains at the end of seven-year mission operation. The model also projects that the signal-to-noise ratios of the RSB will all be larger than the design requirements with a margin of at least 25% at the end of seven years of mission operation. In addition, the detector relative spectral response (RSR) is modulated by the wavelength-dependent optical throughput degradation. We compute the modulated RSR and its impacts on sensor radiometric calibration and the computed top-of-the-atmosphere spectral reflectance at the Sensor Data Record level.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument onboard the Suomi National Polar-orbiting Partnership (S-NPP) spacecraft that was launched on October 28, 2011. VIIRS is designed to provide top of the atmosphere radiometric measurements and imaging of the entire planet Earth twice daily. It is a wide-swath (3040 km) cross-track scanning radiometer with spatial resolutions of 375 and 750 m at nadir for imaging and moderate bands, respectively. It has 22 spectral bands covering the spectrum between 0.4 and 12.5 μm, including 15 reflective solar bands and 7 thermal emissive bands. VIIRS observations are used to generate 22 environmental data records used by various operational applications and for climate research. This paper describes the prelaunch radiometric calibration and characterization methodologies used by the NASA VIIRS Characterization Support Team, including performance assessments for the reflective and emissive band radiometric calibration, the signal-to-noise ratios, dual gain transition, and dynamic range. Other aspects of the sensor performance such as scattered light response, response versus scan angle, polarization sensitivity, relative spectral response, and crosstalk will also be briefly described. A comprehensive set of performance metrics generated during the prelaunch testing program will be compared to the sensor requirements, and a list of lessons learned will be presented to enhance testing and performance assessment for future Joint Polar-Orbiting Satellite System VIIRS sensors.

The S-NPP VIIRS was launched on October 28, 2011 and activated on November 8, and then went through a series of intensive functional tests in order to establish the sensor's baseline characteristics and initial on-orbit performance. With the exception of large optical degradation in the NIR and SWIR spectral regions that is due to pre-launch mirror coating contamination, both the VIIRS instrument and its on-board calibrators continue to operate and function normally. With continuous dedicated effort, it is expected that most of the sensor calibration parameters will continue to meet their design requirements and that high quality data products will be continuously generated and used by the operational as well as research community.

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) spacecraft was launched on October 28, 2011. The S-NPP is orbiting the Earth in a sun-synchronous plane with nominal 13:30 local equatorial crossing time. The VIIRS nadir aperture door was opened on November 21, followed by cryo-cooler door opening on January 18, 2012. The NASA VCST team has carried out a series of VIIRS pre-launch and on-orbit calibration activities and analyses in support of the sensor data records validation and improvement. The sensor and its on-board calibrators have been successfully operated for more than one and a half years.

The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a primary sensor onboard the National Polar-orbiting Partnership (NPP) satellite launched on October 28, 2011. It collects data over the spectral range of 0.4-12.5 um and consists of 15 reflective solar bands (RSB) and 7 thermal emissive bands (TEB). Like the heritage sensor MODIS (MOderate Resolution Imaging Spectroradiometer), VIIRS has a set of On-Board Calibrators (OBC) that provide data for radiometric calibration of the instrument in offline ground processing. The reflective bands use sunlight reflected from a Solar Diffuser (SD) after passing through an attenuating Solar Diffuser Screen (SDS) as a reference illumination source. The emissive bands use an On-Board Calibrator Blackbody (OBC BB) maintained at a constant elevated temperature as a reference illumination source. The Space View (SV) port provides a dark reference scene for background subtraction to remove any detector biases for both reflective and emissive bands.

Automated test data generation is always a hot topic in software engineering, and evolutionary testing (ET) is an emerging and promising technology for this purpose. However, in structural testing, the presence of flag variables lead evolutionary testing degenerate to random testing. All previous work only focused on the flag problem in structural programs, and no attention has been paid to unstructured programs with flag conditions, although numerous industrial real-world programs are of this kind. In this paper, as a further step of the author's research, a fitness calculation rule for flag conditions in unstructured programs is proposed. The experiments on exemplifications recurrent in industrial real-world programs, such as Linux and NS2, show that our new fitness calculation rule could effectively guide evolutionary search to successfully find the required test data at low cost, while all previous approaches failed.