|
The NASA Clouds and the Earth's Radiant Energy System (CERES) energy balanced and filled (EBAF) product provides top of atmosphere SW and LW fluxes for monitoring the Earth’s energy budget and to validate climate models. The current EBAF Ed4.1 products, based on the Terra and Aqua CERES instrument observed radiances, rely on MODIS cloud properties to determine the scene-selected angular distribution model used to convert the CERES radiances into fluxes. The CERES EBAF Ed4.2 product will be based on NOAA-20 CERES observations beginning with the data month of April 2022. A seamless transition of fluxes and clouds can only occur if the analogous MODIS and VIIRS channels are properly inter-calibrated. The spectral response functions (SRF) of these bands differ noticeably and will require scene-dependent spectral band adjustment factors (SBAF) for proper radiometric scaling between them. VIIRS I1 and M5 same-granule reflectance measurements provide the optimal opportunity to validate SBAFs over many surface and cloud conditions. The CERES project maintains SCIAMACHY-, GOME-2-, and Hyperion-based scene-stratified hyper-spectral reflectance measurements that can be convolved with sensor pair SRFs to compute the corresponding SBAFs. The SCIAMACHY 2nd order and GOME-2 linear fit SBAFs were optimal in providing spatially uniform M5/I1 spectrally corrected reflectance ratios over all-sky tropical ocean scenes, which corrected both clear-sky and bright cloud reflectances simultaneously by varying the SBAF as a function of the reflectance. Dome-C and deep convective cloud (DCC) SBAFs had a small M5/I1 SBAF reflectance correction of ~1.03, whereas Libya-4 had a large M5/I1 SBAF reflectance correction of ~1.085. DCC, Dome-C and Libya-4 are spectrally uniform spatial targets with site M5/I1 reflectance ratio spatial homogeneity within 0.2%. The impact of cloud contamination from both the cloud tops and shadows over Libya-4 reduced the M5/I1 reflectance ratio. Over Dome-C, cloud contamination did not significantly shift the M5/I1 reflectance ratio. The Hyperion spectral reflectances are too coarse to be convolved with the narrow M5 SRF, which resulted in M5/I1 SBAFs that differed significantly from those based on SCIAMACHY and GOME-2.
|
