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The National Oceanic and Atmospheric Administration (NOAA)-20 Visible Infrared Imaging Radiometer Suite (VIIRS) was launched on November 18, 2017, and it has been operational for more than two years and follows the first Joint Polar Satellite System (JPSS) series of the Suomi National Polar-orbiting Partnership (S-NPP) mission. VIIRS has 14 reflective solar bands (RSBs) covering a spectral range of 0.41– $2.3~\mu \text{m}$. The primary source of RSB calibration is the solar diffuser (SD), and the time-dependent SD degradation is monitored by the SD stability monitor (SDSM). The initial instability of the SD degradation (H-factor) was resolved by updating SDSM sun screen transmittance function combining yaw maneuver data and on-orbit SDSM data sets. After the H-factor improvements, the VIIRS RSB calibration coefficients (F-factors) are updated and applied to the operational Sensor Data Record (SDR) product generation. To validate the SD F-factors, the lunar F-factors are calculated by using a lunar irradiance model and comparing the trend differences between them. Over the two years of operation, decreasing trends have been calculated with the SD F-factors, whereas constant lunar F-factors were observed in bands M1–M4. With these discrepancies, the operational F-factors remained unchanged since April 2018 because the deep convective cloud (DCC) and cross-calibration comparison results did not show any further degradations in these bands. All the possible radiometric calibration sources, such as SD and lunar F-factors, DCC trends, and cross-calibration results, are monitored, compared, and applied by the NOAA VIIRS SDR science team for the best quality of the VIIRS SDR product. [ABSTRACT FROM AUTHOR]

The accuracy of ocean surface wind vectors measured by satellite-borne scatterometers depends on measured backscattering coefficient (σ°). Hence, an in-flight calibration of a satellite scatterometer is essential as this is not guaranteed by its prelaunch absolute calibration. The postlaunch calibration of σ° is also required to monitor the time evolution of the accuracy of measured σ °. This is performed using relative calibration over land targets with minor spatiotemporal variation of σ°. A few such targets are the Amazon rainforest, Greenland, Antarctica, etc. In this paper, relative calibration of σ° from the OceanSAT-2 Scatterometer (OSCAT) has been carried out by comparing it with a similar quantity from the Quick Scatterometer (QuikSCAT) for November 2009. The differences between the average σ° of QuikSCAT and that of OSCAT have been calculated globally to check the overall consistency. Over the calibration sites, the differences are within ±0.25 dB. Histograms of differences in ascending/descending passes and fore/aft looks of OSCAT have also been analyzed over the calibration sites. These indicate that look bias in OSCAT σ° is within the range of ±0.5 dB. It is also evident that pass biases, i.e., differences between ascending and descending passes, exist over the Amazon rainforest for both QuikSCAT and OSCAT. This diurnal variation in σ° may go up to 1.25 dB in OSCAT. Further, computations of daily average and standard deviation over the calibration site show that mean OSCAT σ° is consistent with mean QuikSCAT σ°, whereas the standard deviation in OSCAT is marginally higher. Further, time-series analysis of OSCAT σ° shows its temporal stability. [ABSTRACT FROM PUBLISHER]

The present paper describes the cross calibration of the Remote Sensing Instrument (RSI) onboard Formosat-2 using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra as a reference, which has been continuously calibrated by means of the onboard and vicarious calibration methods. The data integration system for multi-satellite sensor databases on the Global Earth Observation Grid (GEO Grid) is used in order to find pairs of images acquired by both satellite optical sensors over the radiometric calibration sites on the same days. Radiative transfer simulations that consider different imaging conditions using the Second Simulation of a Satellite Signal in the Solar Spectrum (6S) code are performed based on the Moderate-resolution Imaging Spectroradiometer (MODIS) atmosphere and land products, and the optimum methodology for this cross calibration is discussed under the assumption of no ground-based measurements. The derived calibration coefficients are normalized by the values of preflight calibration and are compared with the results of in-flight cross calibration by the Centre National d'Études Spatiales (CNES) and vicarious calibration described in our previous paper. The average degradations of sensor sensitivity since preflight calibration until 2009 are estimated to be 10% (Band2), 11% (Band3), and 8% (Band4). The derived long-term degradation trends are almost consistent with the results of our vicarious calibration within the precision. The cross-calibration methodology used in the present paper facilitates the in-flight radiometric calibration of satellite optical sensors. [ABSTRACT FROM AUTHOR]