Evaluation of the spectral misalignment on the Earth Clouds, Aerosols and Radiation Explorer/multi-spectral imager cloud product

[摘要] A cloud identification and profiling algorithm is beingdeveloped for the multi-spectral imager (MSI), which is one of the fourinstruments that the Earth Clouds, Aerosols, and Radiation Explorer(EarthCARE) spacecraft will feature. During recent work, we noticed that the MSI response function could shift substantially among some wavelengths (0.67 and 1.65  µ m bands) owing to the spectral misalignment (SMILE), in which a shift in the center wavelength appears as a distortion in the spectral image. We evaluated how SMILE affects the cloud retrieval product qualitatively and quantitatively. We chose four detector pixels from bands 1 and 3 with the nadir pixel as the reference to elucidate how the SMILE erroraffects the cloud optical thickness ( τ ) and effective cloud dropletradius ( r e ) by simulating the MSI forward radiation with ComprehensiveAnalysis Program for Cloud Optical Measurement (CAPCOM). We also evaluatedthe error in simulated scenes from a global cloud system-resolving model and a satellite simulator to measure the effect on actual observation scenes. For typical shallow warm clouds ( τ   =  8, r e   =  8  µ m), the SMILE error on the cloud retrieval was not significant in most cases (up to 6 % error). For typical deep convective clouds ( τ   =  8, r e   =  40  µ m), the SMILE error on the cloud retrieval was evenless significant in most cases (up to 4 % error). Moreover, our resultsfrom two oceanic scenes using the synthetic MSI data agreed well with theforward radiation simulation, indicating that the SMILE error was generallywithin 10 %. Generally, this negligible impact of the SMILE is true forwater surfaces, but it still needs to be investigated further for landsurfaces in future works.

[学科分类] 内科医学