The infrared Fourier spectrometer is based on interferometric spectroscopy, which features high spectral resolution and high sensitivity. Due to the ultra-fine spectral resolution of infrared hyperspectral atmospheric detection instruments, minor errors in spectral calibration can cause radiation measurement errors. High precision spectral calibration is an important prerequisite for quantitative inversion and the application of infrared remote sensing. The spectral calibration accuracy is affected by the limited field of view and off-axis effect. The traditional method is to obtain the spectral calibration coefficient by fitting multiple spectral lines. However, for issues such as ultra-high spectral resolution and wide observation spectral bands, most spaceborne infrared hyperspectral instruments employ forward modeling methods to build instrument spectral response models and remove various spectral effects.

Based on the optical field of view characteristics, we conduct spectral simulations of limited field of view and off-axis effect, and study spectral correction methods for the plane array Fourier spectrometer. Firstly, the influence of instrument line shape function (ILS) is analyzed to determine the analysis methods for different influencing factors (such as finite optical path difference, finite field of view, and off-axis effect). Next, by taking a planar circular detector as an example, the ILS function is constructed by combining the optical characteristics of the instrument itself. Then, the spectral calibration error and spectral sensitivity caused by the off-axis effect are simulated by gas absorption spectroscopy. Finally, test data of the optical field of view is obtained via slit scanning. Based on the pre-launch spectral calibration data of FY-3F/HIRAS-Ⅱ, spectral correction and calibration accuracy verification are carried out.

The experimental results indicate that the limited field of view and off-axis effect cause the spectrum to broaden and shift to a low wavenumber direction. There is a quadratic relationship between the off-axis angle θ_rc and the pixel field of view angle θ_R and the spectral calibration accuracy. The off-axis angle is more sensitive, and its contribution to the spectral calibration accuracy is much greater than that to the pixel field of view angle. When θ_R =60′, the error caused by measurement accuracy of 2′ is approximately 1.3×10^-6. When θ_rc =101.82′(-72′, 72′), the error caused by the measurement accuracy of 2′ in a certain direction is about 12×10^-6. After spectral calibration and correction, the spectral calibration accuracy of the center worst pixel decreases from -24.69×10^-6 to 0.54×10^-6, and the edge worst pixel reduces from -513.38×10^-6 to -0.15×10^-6. All pixels in the three bands meet the indicator requirement of less than 7×10^-6.

Based on the characteristics of the infrared hyperspectral atmospheric detector for the FY-3F satellite, the ILS function and spectral comprehensive effect matrix are constructed. The sensitivity analysis is conducted on the spectral calibration accuracy. By adopting the simulated results of HITRAN as the standard spectral line, the spectral calibration accuracy of long-wave NH₃ absorption spectral lines under different off-axis angles and pixel field of view angles is studied. There is a quadratic function relationship between the spectral calibration accuracy and the angles. The sensitivity to off-axis angles is much higher than that to the pixel field of view angles, the spectral calibration accuracy of the central pixel is -18.84×10^-6, and the spectral calibration accuracy of the outermost pixel is -451×10^-6. Meanwhile, the spectral calibration accuracy caused by position error and pixel size error under the existing optical field of view testing conditions is 1.3×10^-6 and 12×10^-6 respectively. We have studied pre-launch spectral calibration and calibration methods based on instrument optical characteristics and completed the pre-launch spectral performance evaluation of FY-3F/HIRAS-Ⅱ. After spectral correction, the maximum spectral calibration accuracy of each pixel in the three bands is 2.23×10^-6, which meets the spectral calibration index requirement of 7×10^-6. Additionally, our study also has guiding significance for designing and testing optical field parameters in the future and improving spectral calibration accuracy.