Implementation of the Community Radiative Transfer Model in Advanced Clear‐Sky Processor for Oceans and validation against nighttime AVHRR radiances

Abstract

The fast Community Radiative Transfer Model (CRTM) has been integrated into National Environmental Satellite Data and Information Service's newly developed Advanced Clear‐Sky Processor for Oceans (ACSPO). CRTM is used in conjunction with the National Centers for Environmental Prediction (NCEP) Global Forecast System atmospheric profiles and Reynolds weekly version 2 sea surface temperatures (SST) to simulate clear‐sky brightness temperatures (BT). Model BTs are used to improve the ACSPO clear‐sky mask, monitor quality of advanced very high resolution radiometer (AVHRR) BTs, and explore physical SST retrievals. This paper documents CRTM implementation in ACSPO version 1 and evaluates nighttime “model minus observation” (M‐O) BT biases in three bands (3.7, 11, and 12 μm) of four AVHRR/3 instruments onboard NOAA‐16, NOAA‐17, NOAA‐18, and MetOp‐A. With careful treatment of input atmospheric and SST data, the agreement is generally good, showing only weak dependencies of M‐O biases on view zenith angle, column water vapor, and wind speed. The agreement improves if Reynolds weekly SST is used instead of NCEP SST. Including surface reflection also reduces the M‐O bias. After all optimizations, the M‐O biases are within several tenths of a Kelvin. Consistency between different platforms is ∼0.1K, except for NOAA‐16 channel 3B, which is biased low compared to other platforms by ∼0.4K. Our future plans include extending the analyses to daytime data and exploring physical SST retrievals. A web‐based tool is being established to continuously monitor the M‐O biases and physical SSTs. The validation methodology employed in this paper will be used to quantitatively measure the effect of each improvement on the M‐O bias and physical SST.