Intercalibration of Advanced Himawari Imager's Infrared Channels With IASI/Metop-B 1C Data

Abstract

This work addresses the intercalibration of infrared channels 7 to 16 of the Advanced Himawari Imager (AHI) aboard Himawari-8 against the hyperspectral channels of the Infrared Atmospheric Sounding Interferometer (IASI) on board Metop-B using the hyperspectral convolution method. The matching measurements in January, March, July, and November 2016 are collected over a tropical intercalibration area (100 °E∼180 °E, 10 °S∼10 °N) under the conditions of collocation, absolute observation time difference of less than 5 min ${(\vert \Delta \text{time}\vert } , absolute viewing azimuth angle difference of less than 10° ${(\vert \Delta \text{VAA}\vert } , and ${{\vert \cos}}\,\theta _{1}{{/ \cos}}\,\theta _{2}-{{ 1\vert }} , where $\theta _{1}$ and $\theta _{2}$ are the viewing zenith angles of AHI and IASI measurements, respectively. The daytime matching measurements in the channel 7 (centered at about ${\text{3.88 }} \mu {\text{m}}$ ) contaminated by strong and fast changing specular reflected solar irradiance have weak correlation and consequently are excluded from the intercalibration. The results show that the AHI and IASI matching measurements have strong linear correlation, and the intercalibration coefficients (slope and intercept) are obtained through linear regression on the qualified matching measurements. The linear fit results indicate that the in-orbit calibration of the AHI infrared channels is stable in the four months; however, more or less calibration biases exist against IASI/Metop-B hyperspectral channels. The intercalibration results in this work are basically consistent with that of the Meteorological Satellite Center of Japan Meteorological Agency.