Inter-calibration of VIRR/FY-3A/B split-window channels with AIRS/Aqua and IASI/Metop-A measurements

Abstract

ABSTRACTThis work addressed the inter-calibration of the two split-window channels 4 and 5 (IR4, around 10.8 µm; IR5, around 12.0 µm) of Visible and Infrared Radiometer (VIRR) aboard FengYun 3 (FY-3) A and B satellites against the hyperspectral channels of Atmospheric Infrared Sounder (AIRS) on Aqua and Infrared Atmospheric Sounding Interferometer (IASI) on Metop-A over the Arctic area (180ºW–180ºE, 60ºN–90ºN) using the hyperspectral convolution (HSC) method in June and December of 2010–2013. First, the satellite data were re-sampled into the gridded study area using the area-weighted pixel-aggregation method. Then, besides the collocation condition, the measurements acquired by different instruments were matched with the following criteria: 1) the absolute observation time difference is less than 20 min (|∆time|< 20ʹ), and 2) |cosθ1 /cosθ2 – 1|< 0.015, where θ1 and θ2 are the at-surface view zenith angles (VZAs) of the VIRR/FY-3 measurement and the hyperspectral measurement, respectively. Finally, linear regression analyses on the matching measurements were carried out to obtain the inter-calibration coefficients, and re-calibrated VIRR/FY-3A/B measurements were achieved. The results showed that the calibrations of AIRS/Aqua and IASI/Metop-A channels were quiet consistent, whereas, against the hyperspectral channels, the calibrations of VIRR/FY-3A/B channels 4 and 5 were biased, and they presented certain seasonal and annual variations, especially for VIRR/FY-3A channel 4. In contrast to VIRR/FY-3A channels, the calibration discrepancies of VIRR/FY-3B channels 4 and 5 were smaller. Moreover, no obvious impact of solar illumination on VIRR/FY-3A/B measurements was observed.