AVHRR, MODIS, and VIIRS radiometric stability and consistency in SST bands

Monitoring of IR Clear‐Sky Radiances over Oceans for SST (MICROS; www.star.nesdis.noaa.gov/sod/sst/micros ) is NESDIS near‐real time web‐based radiance monitoring system. It analyzes Model (Community Radiative Transfer Model, CRTM) minus Observation (M‐O) biases in brightness temperatures (BT) in three bands centered at 3.7 (IR37), 11 (IR11), and 12 µm (IR12), for several AVHRR (NOAA‐16, ‐17, ‐18, ‐19, Metop‐A, ‐B), VIIRS (Suomi National Polar Partnership, S‐NPP), and MODIS (Terra, Aqua) sensors. Double‐differences (DD) are employed to check BTs for radiometric stability and consistency. All sensors are stable, with the exception of two AVHRRs, onboard NOAA‐16 and to a lesser extent NOAA‐18, and generally consistent. VIIRS onboard S‐NPP, launched in October 2011, is well in‐family, especially after its calibration was fine‐tuned on 7 March 2012. MODIS M‐O biases were initially out‐of‐family by up to −0.6 K, due to incorrect CRTM transmittance coefficients. Following MICROS feedback, CRTM Team updated coefficients and brought MODIS back in‐family. Terra and Aqua BTs are very consistent in IR11 and IR12 but show cross‐platform bias of 0.3 K in IR37, likely attributed to MODIS characterization. Work with MODIS Characterization Support Team is underway to resolve this. Initial analyses of AVHRR onboard Metop‐B launched in September 2012 suggest that its BTs are offset from Metop‐A by up to ∼0.3 K. Overall, MICROS DDs are well suited to evaluate the sensors stability, but dedicated effort is needed to ensure consistent radiative transfer modeling (RTM) calculations for various sensors before DDs can be used in Global Space‐based Inter‐Calibration System (GSICS) quantitative applications.