Jinghua Mao

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.

China's two ultraviolet-visible atmospheric composition detectors — the Absorbing Aerosol Sensor (AAS), launched in 2021, and the Ozone Monitor Suite-Nadir (OMS-N), launched in 2023 — both provide daily global coverage. They are carried on the morning-orbit satellites GaoFen-5B and FengYun-3F, respectively, which enables mutual calibration between the two instruments. AAS offers a spectral resolution of 1.5 nm and a nadir spatial resolution of 2 km × 4 km, and is primarily designed to observe atmospheric aerosol pollution. OMS-N, in its main observation band, achieves a spectral resolution of 0.6 nm and a nadir spatial resolution of 7 km × 7 km. Its objectives include monitoring total ozone and its vertical profile, trace gases such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and formaldehyde (HCHO), as well as retrieving aerosol and cloud information.Using wavelengths of 354 nm and 388 nm, we successfully obtained Ultraviolet Aerosol Index (UVAI) products from both payloads. These products were validated against GOME-2, which is also onboard a morning-orbit satellite, and the retrieval results from AAS and OMS-N were cross-compared. We utilized the UVAI products to observe pollution processes in the China region, the Indochina Peninsula, and the Indian region, as well as global dust belts and wildfire smoke plumes.We also obtained preliminary near-ultraviolet Aerosol Optical Depth (AOD) retrieval results using the OMAERUV method and validated them with AERONET data. The retrieval algorithm will be continuously refined going forward, and efforts will be made to acquire other aerosol products.

As one of the payloads on board the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) spacecraft, the ultraviolet imager (UVI) aims to capture N2 Lyman–Birge–Hopfield (LBH) aurora continuously on a high-eccentricity orbit. The UVI instrument includes an intensified charge-coupled device (ICCD) for far ultraviolet (FUV) wavelength. It comprises a sealed image intensifier, a relay lens system, a CCD, and a mechanical housing. ICCD’s performance characteristics are evaluated before integrating with the optical system of the UVI, including the quantum efficiency, radiant gain, background characteristics, excess noise factor, image quality, and signal-to-noise ratio (SNR). The testing procedure and results are presented and discussed. The results demonstrate that the comprehensive performance of the detector is good, and provide critical technical support for quantitative applications.

The aurora is the optical manifestation of the global magnetospheric dynamics. Optical imaging of aurora provide insight into the large-scale convections and wave-particle interactions in the magnetosphere, thus provide important information on the mass and energy flow in the solar wind-magnetosphere coupling system. The Ultraviolet Imager (UVI) onboard the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) satellite will image the entire auroral oval in N2 Lyman-Birge-Hopfield (LBH) band (160–180 nm) while effectively mitigating contamination from dayglow, achieving a spatial resolution of approximately 100 km or better. The SMILE spacecraft operates in a highly eccentric orbit characterized by an orbital period of approximately 50 hours. This orbit configuration is particularly well-suited for long-term continuous monitoring of northern auroras. Such insights will significantly enhance our research into energy deposition processes occurring within the ionosphere and upper atmosphere during solar wind-magnetosphere interactions. Here, we will introduce in detail the instrument, laboratory calibrations, in-flight calibration plan, and data products of SMILE UVI.

An Ultraviolet-Visible Hyperspectral Sensors (UVS) instrument is an ultraviolet-visible imaging spectrograph equipped with two-dimensional charge-coupled device detectors. It records both the spectrum and the swath perpendicular to the flight direction, offering a wide 112° swath. This configuration enables global daily ground coverage with high spatial resolution. The absolute values of in-orbit solar irradiance can be evaluated using the bidirectional reflectance distribution function (BRDF), with the measurement accuracy directly affecting the accuracy of constituent inversion. This paper outlines the calibration process for the BRDF of the UVS, detailing the calibration methods and equipment used. It also proposes a BRDF model and discusses key coefficients. The accuracy levels of the UVS in the UV1, UV2, and VIS channels were 2.162%, 2.162%, and 2.173%, respectively.

The Absorbing Aerosol Index (AAI) determines the presence and approximate amount of absorbing aerosol particles. The Absorbing Aerosol Sensor (AAS) equipped on the Gaofen-5B satellite was successfully launched and deployed in orbit on September 7, 2021. Following a period of initial on-orbit testing, reliable AAI observational results were collected. The nadir of the AAS had a design spatial resolution of 4 km × 4 km and a current spatial resolution of 2 km × 4 km, which presented significant benefits in the spatial resolution and clear distribution characteristics of pollutants. The results of AAS were validated by comparing with the observed data of Global Ozone Monitoring Experiment-2 (GOME-2) in the Sahara Desert and surrounding areas. In 2022 and 2023, we utilized AAS observations to study the typical pollution processes. These included the spring pollution distribution around the Bohai Sea, the observation and tracking of long-term dust pollution in China in March and April 2023, the distribution of spring pollution in the Indochina Peninsula in April 2023, and the distribution of wildfires in Canada on June 22, 2023. The results were validated and analyzed using data from Tropospheric Monitoring Instrument (TROPOMI), GOME-2, AErosol RObotic NETwork (AERONET) and Moderate-resolution Imaging Spectroradiometer (MODIS). The results of the observation and evaluation revealed that the AAS AAI can provide reliable information for precise observation of air pollutants at a high resolution.

The Ozone Monitoring Suite-Nadir (OMS-N) instrument is the first hyperspectral remote sensor in the ultraviolet band of China’s Fengyun series satellites. It can be used to detect several kinds of atmospheric constituents. This paper describes the prelaunch spectral calibration of the OMS-N onboard FengYun 3F. Several critical spectral parameters including the spectral resolution, spectral dispersion, and the instrument spectral response function were determined through laser-based measurements. A secondary peak of the instrument spectral response function from the short wavelength side of the ultraviolet band was found, and the possible influence on data applications was analyzed using a reference solar model and radiative transfer model. The results indicate that the spectral resolution and spectral accuracy of OMS-N meet the mission requirements. However, the asymmetries in the instrument spectral response function in the ultraviolet band were found near nadir rows, which are expressed as the “asymmetric central peak” and “secondary peak”. The analysis results show that if the influences of the instrument spectral response function “asymmetric central peak” and “secondary peak” in the ultraviolet band are ignored, they will bring an error as large as 5% at the center of the absorption line.

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 3 August 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 VIS channel, 3% for the UV1 channel, and 2.2% for the UV2 channel. Furthermore, the uncertainty of the radiometric calibration was analyzed. The results indicated an absolute uncertainty of 2.33% for both the UV1 and UV2 channels and 1.69% for the VIS channel. The relative uncertainty was 1.84% for both the UV1 and UV2 channels and 1.45% for the VIS channel. 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.

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.