Ning Lei

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key Earth-observing satellite sensor utilized to generate nearly 30 products for environmental studies and weather forecasting. Fourteen of the 22 VIIRS spectral bands are reflective solar bands (RSBs), which are calibrated on orbit through a sunlit solar diffuser (SD). Upon exposure to the Sun, the SD’s bidirectional reflectance distribution function (BRDF) changes its value, quantified by the H-factor. We observe that the H-factor depends on the location of the SD surface. Here, we compare the H-factor SD positional dependence across the three VIIRS instruments currently in operation, aboard the SNPP, the N20, and the N21 satellites. We determine the relative amount of solar exposure using the temporal trend difference in the H-factor before and after the nadir door is opened. Using the relative amount of solar exposure, we derive the striping model coefficients which generally agree well with the published values. Hence, our methodology can be applied early to destripe future VIIRS RSBs.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is an Earth-observing satellite sensor. Out of the 22 VIIRS spectral bands, five are the short-wave infrared (SWIR) bands. Earth views of these bands for the VIIRS instrument aboard the NOAA-20 (N20) satellite have unexpected striping. The scene spectral radiance is retrieved by using a cubic polynomial of the background removed detector digital number with the offset set to zero. To minimize the striping, we develop an algorithm to find the offsets from the striping assessments of the satellite images of the Sahara Desert, deep convective clouds (DCCs) around the equator, and the Moon. We use the average of the offsets obtained from these three scenes and the other coefficients in the original cubic polynomial to update the polynomial coefficient look-up-table that is used for the NASA N20 VIIRS top-of-the-atmosphere spectral radiance and reflectance retrievals in Collection 2.1. After the application of the derived offsets, the striping from the scenes and the Libya 4 Desert is significantly reduced, except bands I3 and M10 over the DCC scene. For the DCC scene, the original striping for bands I3 and M10 is reduced but not significantly. In the case that the quadratic term in the polynomial also contributes to the observed striping, we further develop an algorithm to find both the offset and the quadratic term coefficient from striping assessments of two scenes whose spectral radiance levels differ significantly.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is one of the key instruments on the recently launched NOAA-21 (previously known as JPSS-2) satellite. The VIIRS, like its predecessors on the SNPP and NOAA-20 satellites, provides daily global coverage in 22 spectral bands from 412 nm to 12 μm. The geometrically and radiometrically calibrated observations are the basis for many operational applications and scientific research studies. A total of 14 of the 22 bands are reflective solar bands (RSBs), covering photon wavelengths from 412 nm to 2.25 μm. The RSBs were radiometrically calibrated prelaunch and have been regularly calibrated on orbit through the onboard solar diffuser (SD) and scheduled lunar observations. The on-orbit SD’s reflectance change is determined by the onboard solar diffuser stability monitor (SDSM). We review the calibration algorithms and present the early mission performance of the NASA N21 VIIRS RSBs. Using the calibration data collected at both the yaw maneuver and regular times, we derive the screen transmittance functions. The visible and near-infrared bands’ radiometric gains have been stable, nearly independent of time, and so were the radiometric gains of the shortwave-infrared bands after the second mid-mission outgassing. Further, we assess the Earth-view striping observed in the immediate prior collection (Collection 2.0) and apply a previously developed algorithm to mitigate the striping. The N21 VIIRS RSB detector signal-to-noise ratios are all above the design values with large margins. Finally, the uncertainties of the retrieved Earth-view top-of-the-atmosphere spectral reflectance factors at the respective typical spectral radiance levels are estimated to be less than 1.5% for all the RSBs, except band M11 whose reflectance factor uncertainty is 2.2%.

Inaccurate solar vector orientation knowledge can considerably deteriorate calibration results for the Visible Infrared Imaging Radiometer Suite (VIIRS). We develop a methodology to use the Suomi National Polar-orbiting Partnership (SNPP) VIIRS solar diffuser stability monitor (SDSM) sun view data to assess the knowledge accuracy of the solar angles that reside in the onboard calibrator intermediate product (OBCIP) files used for on-orbit radiometric calibration. We applied an initial version of this methodology in 2013 and found that the solar declination angle had a relative error that varied between ∼0 deg to 0.17 deg. The relative error is referenced to the error at the SNPP satellite yaw maneuver time that occurred on February 15 to 16, 2012. Our mission long results from the current methodology show that the solar vector angular knowledge error occurred from the early mission until mission day 1129 (November 30, 2014). The error undulates yearly with the largest error in the solar declination angle increasing from ∼0.17 deg in the first year to 0.19 deg in the third year, agreeing with the solar vector error root cause understanding realized in early 2014. With the reprocessed OBCIP files, we find the solar vector declination and azimuth angular knowledge errors have near zero biases. The detection limit of this methodology strongly depends on how finely the solar angle is sampled by the SDSM detectors. With the SDSM sun view data collected when the SDSM operated once per day, this methodology yields detection standard deviations of 0.013 deg and 0.024 deg for the solar declination and azimuth angles. With a 3-sigma criterion, at the detection limits, the solar orientation errors result in a calibration error of 0.088%. This method can be applied to other Earth-orbiting sensors.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument on the recently launched NOAA-21 (previously JPSS-2) satellite. The VIIRS, like its predecessors on the SNPP and NOAA-20 satellites, provides daily global coverage in 22 spectral bands from 0.41 to 12.0 micrometers. The geometrically and radiometrically calibrated observations are the basis for numerous operational applications and scientific research studies. Fourteen of the 22 bands are reflective solar bands (RSBs), covering wavelengths from 0.41 to 2.25 micrometers. The RSBs were radiometrically calibrated prelaunch and are regularly calibrated on orbit through the onboard solar diffuser (SD) and scheduled lunar observations. The on-orbit SD’s reflectance change is determined by the onboard solar diffuser stability monitor (SDSM). Here, we report our findings on the early mission NOAA-21 VIIRS RSB radiometric performance, and the performance of the SD and the SDSM.

The VIIRS instrument on the NOAA-20 satellite continues to have excellent performance in its reflective solar bands (RSB), with detector gains changing by less than 0.5% over the first four and a half years of the mission. The calibration of the RSB for NASA’s Collection 2 Level 1B product relies primarily on data from the on-board solar diffuser (SD). Recently, we updated the calibration algorithm to include corrections to the long-term gain trends based on regularly scheduled lunar observations. Earlier in the NOAA-20 mission, due to insufficient lunar data, the long-term correction applied to the SD trends was based on scaled results from the first VIIRS instrument on the SNPP satellite. In this paper, we show updated NOAA-20 data trends of the solar diffuser degradation and the RSB gains derived from every-orbit SD observations. We also show updated lunar data and describe our algorithm for using the lunar data to correct the long-term gain trends. The gain differences between the previous algorithm, using scaled SNPP lunar data, and new algorithm, directly using NOAA-20 lunar data, are largest for bands M2 (0.4%), M3 (0.4%), M4 (0.5%), and I1 (0.6%), and negligible (<0.2%) for the other RSB. The updated algorithm began to be implemented in forward production of the NASA VIIRS Level 1B product starting in September 2021 and will allow for more accurate tracking of the long-term RSB gain in the future.

The Earth-observing Visible Infrared Imaging Radiometer Suite (VIIRS) has 14 reflective solar bands (RSBs), covering wavelengths from 412 to 2250 nm. The first VIIRS instrument is aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite launched on October 28, 2011. The RSBs use a sunlit onboard solar diffuser (SD) to calibrate, with the dark count obtained through viewing the Space View (SV) port. Stray light contaminations in the SV and/or the SD View, if present, could negatively impact on the radiometric calibration accuracy. Here, we assess the stray light contamination in the SNPP VIIRS Space View, focusing on band M1 (412 nm).

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.

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) has successfully operated on-orbit for nearly ten years since its launch in October 2011, continuously making global observations and improving studies of changes in the Earth’s climate and environment. VIIRS has 22 spectral bands, among which 14 are reflective solar bands (RSBs) covering a spectral range from 0.41 to 2.25 μm. The SNPP VIIRS RSBs are primarily calibrated by the onboard solar diffuser (SD), with its on-orbit degradation tracked by an onboard SD stability monitor (SDSM). The near-monthly scheduled lunar observations, together with the sensor responses over stable ground targets, have contributed to the sensor’s mission-long on-orbit calibration and characterization. Numerous improvements have been made in the RSB calibration methodology since SNPP VIIRS was launched, and the RSB calibration has reached a mature stage after almost ten years of on-orbit operation. SNPP is a joint NASA/NOAA mission and there are two teams, the NASA VIIRS Calibration Support Team (VCST) and the NOAA VIIRS Sensor Data Record Team, which are dedicated to SNPP VIIRS on-orbit calibration. In this paper, we focus on the calibration performed by the NASA VCST. The SNPP VIIRS RSB calibration methodologies used to produce the calibration coefficient look up tables for the latest NASA Level 1B Collection 2 products are reviewed and the calibration improvements incorporated in this collection are described. Recent calibration changes include the removal of image striping caused by non-uniform degradation of the SD, improvements to the method for combining lunar and SD data, mitigation of the effects due a recent anomaly in the SD measurements, estimation of the SD degradation beyond 935 nm, and fitting strategy improvements for look-up table delivery. Overall, the SNPP VIIRS RSBs have performed well since its launch and continue to meet design specifications.

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.