In-Flight, Full-Pixel Calibration of Reflectance in Spatial Dimension for Environmental Trace Gases Monitoring Instrument

Calibrating the top-of-atmospheric reflectance measurements of spaceborne hyperspectral atmospheric composition monitoring instruments is necessary to ensure the accuracy during cloud and aerosol retrieval. Here, we present a method for calibrating full-pixel reflectance data collected by the Environmental Trace Gases Monitoring Instrument (EMI). This method compares EMI reflectance data with simulation using a radiative transfer model (RTM). To simplify the radiative transfer calculations, a clear observation situation without clouds or aerosols was chosen. Correction coefficients for each spatial dimensional pixel were obtained by comparing the EMI Earth reflectance with the simulated reflectance under clear sky conditions. The corrected reflectance data were cross-compared with Tropospheric Monitoring Instrument (TROPOMI) reflectance data, highlighting that there were relative errors of >20% at 345, 388, 425, and 440 nm before correction. After correction, however, the errors of all selected wavelength bands were < 5%, demonstrating that the developed method can help in calibrating EMI in-flight reflectance measurements.