LAUSR

This paper addresses the intercalibration of the infrared channels 1–19 of Infrared Atmospheric Sounder (IRAS) on FengYun 3B (FY-3B) against the hyperspectral channels of the infrared atmospheric sounding interferometer (IASI) aboard Metop-A. Matching measurements were collected over the Arctic area (60 °N–90 °N) and Antarctic area (60 °S–90 °S) with collocation, absolute observation time difference of less than 20 min (|Δtime| < 20 min), and |cosθ₁/cosθ ₂ − 1| < 0.02, where θ₁ and θ ₂ are, respectively, the viewing zenith angles of IRAS/FY-3B and IASI/Metop-A measurements. The results show that the measurements in channels 1–12, 14, and 15 are linearly related to the convolved IASI/Metop-A measurements, and no obvious impact of direct solar illumination on these channels is observed. Although the measurements in channels 13, and 16–18 are also linearly related to the convolved IASI/Metop-A measurements, they are strongly influenced by direct solar illumination: The measurements with satellites illuminated by the Sun and with satellites in the Earth shadow are distributed on different lines. The measurements in channels 18 and 19 present certain nonlinear characteristics. Against the convolved IASI/Metop-A measurements, the measurements in IRAS/FY-3B channels 1–12, 14–17, and 19 were averagely 1.0–2.0 K underestimated, whereas the measurements in IRAS/FY-3B channels 13 and 18 were 2.0–4.0 K overestimated. Linear/nonlinear regressions were conducted on the matching measurements and intercalibration coefficients were obtained. Corrections of the measurements in IRAS/FY-3B channels 1–19 with the intercalibration indicate that the calibration of IASI/Metop-A hyperspectral channels was successfully transferred to IRAS/FY-3B channels 1–19.