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Integrated Cal/Val of IR SmallSat Sensor


SNO-based Inter-IR Sensor Radiometric Bias Evaluation

The Simultaneous nadir Overpass (SNO) event selection criteria usually includes cloud screening, nadir view, and confined time and distance difference. Comparison of simultaneous measurements between two or more IR sensors at their orbital intersection under nearly identical viewing conditions makes this approach highly suitable for reducing the uncertainties associated with the atmospheric variability. Using CrIS on NPP and NOAA-20, and IASI on MetOp-A satellite as proxy SmallSat hyperspectral IR instruments, SNO-based Cal/Val technique for IR sensor has been developed, implemented and evaluated to provide assessment of challenges in calibration and validation of SmallSat data.

Figures below show inter-IR sensor brightness temperature bias determined with SNO method. Double difference of SNO-based radiometric bias enables inter-comparison of IR sensor pair without SNOs. Construction of SNO-based radiometric bias map provides systematic and searchable means to inter-compare radiometric qualities among swam of sensors and makes SmallSat sensor quality traceable to legacy sensors.


Example of SNO-based BT Bias Evaluation among IR Sensors


image: Image acquired by SmallSat

Construction of SNO-based Inter-IR sensor BT bias Map


image: Image acquired by SmallSat

O-B Bias Evaluation for IR Sensor

O-B bias analysis scheme enables evaluation of spectral radiometric bias of SmallSat IR sensor w.r.t. atmospheric reanalysis background data through comparison with the Community Radiative Transfer Model (CRTM)-modeled brightness temperature (BT) using the global atmosphere reanalysis data from European Centre for Medium-Range Weather Forecasts (ECMWF). In the figure below, NPP and NOAA-20 CrIS sensor data are used as the proxy SmallSat IR sensor data to demonstrate the prototype O-B based SmallSat IR sensor Cal/Val system. ECWMF global reanalysis data on 11 June 2018 have been used in the radiative transfer modeling.


O-B Bias between NPP/NOAA-20 CrIS BT and CRTM-modeled BT and BT Bias
between NPP and NOAA-20 CrIS with Double-Difference


image: Image acquired by SmallSat


Inter-IR/RO Sensor Bias Evaluation

The evaluation of temperature bias between IR and RO instruments on SmallSat is enabled through inter-comparison between
CRTM-simulated BT from RO (COSMIC/MetOp-A/B) measurement and observed BT by proxy IR SmallSats. NPP and NOAA-20
CrIS are used as the proxy SmallSat IR sensors. Figure below shows example of inter-instrument (IR vs. RO) comparison with radiative transfer modeling.


Inter-comparison of NPP/NOAA-20 CrIS BT and CRTM-modeled BT using RO
Temperature/Humidity Profiles and NPP vs. NOAA-20 CrIS BT Bias


image: Image acquired by SmallSat