Jinduo Wang

The Ozone Monitor Suite-Nadir (OMS-N) onboard the FY-3F satellite is a key payload for global atmospheric ozone and trace gas detection. The data quality depends on the accuracy of ground calibration. This study presents a systematic ground calibration of OMS-N. The instrument operates over 250–500 nm, with a spatial resolution of 7 × 7 km² and a spectral resolution of 0.5–1 nm. Radiometric calibration was performed using an integrating sphere, spectral calibration using a tunable laser, and geometric calibration using a precision turntable. All tests were conducted under controlled environmental conditions (20 ± 3 °C and 50% ± 10% humidity). The absolute radiometric calibration uncertainty was below 2.33% for UV1/UV2 and 1.69% for VIS, with relative uncertainties ≤1.84%. The spectral wavelength error was ≤0.01 nm for the VIS channel and ≤0.03 nm for the UV1/UV2 channels, and the geometric positioning uncertainty was better than 0.1 pixels. All performance indicators met or exceeded the design requirements. These results provide technical support for the quantitative application of OMS-N data in atmospheric monitoring and establish a reference framework for the ground calibration of similar ultraviolet hyperspectral instruments.

This paper presents the prelaunch radiometric calibration of the Ozone Monitor Suite - Nadir (OMS-N) instrument, a vital payload on the FY-3F satellite. FY-3F achieved a successful launch on August 3, 2023. The radiance calibration of the OMS-N instrument was achieved using an integrating sphere, with known exit radiance ascertained through a transferring radiometer. The calibration model incorporates six energy levels. The Solar Simulator Standard System was employed to validate the calibration results, selecting specific rows to represent varying spatial dimensions. Considering the influence of xenon lamp characteristic peaks and transmission errors during the calibration process, the average deviation remained within 2.3% for the UVIS channel, 3% for the UV1 channel, and 2.2% for the UV2 channel. Furthermore, this study analyzed the uncertainty of the radiometric calibration. The results indicated an absolute uncertainty of 2.32% for both UV1 and UV2 channels, while the VIS channel exhibited an uncertainty of 1.67%. The relative uncertainty was 1.84% for both UV1 and UV2 channels, with the VIS channel exhibiting an uncertainty of 1.45%. The obtained calibration coefficients are accurate and reliable and can be used for the inversion of product parameters, which is of great significance to the quantitative application of satellite data and the advancement of scientific research on quantitative remote sensing.

Spectral calibration consists of the calibration of wavelengths and the measurement of the instrument’s spectral response function (SRF). Unlike conventional slits, the absorbed aerosol sensors (AAS) are used as a slit homogenizer, in which the SRF is not a conventional Gaussian curve. To be more precise, the SRF is the convolution of the slit function of the spectrometer, the line spread function of the optical system, and the detector response function. The SRF of the slit homogenizer is a flat-topped multi-Gaussian function. Considering the convenience of fitting, a super-Gaussian function, which has a distribution similar to the flat-topped multi-Gaussian function, is employed to fit the measured data in a spectral calibration. According to the results, the SRF’s shapes resembling a Gaussian curve with a flat top could be derived, which contains a full width at half maximum (FWHM) of 1.78–1.82 nm for the AAS. The results show that the correlation is about 0.99, which indicates the usefulness of the fitting function that could better characterize the SRF of the instrument.

Spectral calibration consists of the calibration of wavelengths and the measurement of the instrument's spectral response function (SRF). Unlike conventional slits, the absorbed aerosol sensors (AAS) are used as a slit homogenizer, in which the spectral response function (SRF) is not a conventional Gaussian curve. To be more precise, the SRF is the convolution of the slit function of the spectrometer, the line spread function of the optical system, and the detector response function. The SRF of the slit homogenizer is a flat-topped multi-Gaussian function. Considering the convenience of fitting, a super-Gaussian function, which looks like a similar distribution to the flat-topped multi-Gaussian function, is used to fit the measured data in a spectral calibration. According to the results, the SRF’s shapes, due to the Earth port, resemble a Gaussian curve with a flatted top could be concluded, which contains an FWHM of 1.78–1.82 nm for the AAS. The results show that the correlation coefficients are about 0.99, which proves that the fitting function could better characterize the SRF of the instrument.