Limb sounding can provide fine vertical profiles of atmospheric constituents, while tangent height (TH) offsets are the primary source of uncertainty in limb sounding. Due to the absence of a star tracker, the Ozone Monitoring Suite-Limb (OMS-L) aboard the Fengyun-3F (FY-3F) satellite cannot provide direct geometric references for TH validation, making it difficult to quantify the TH offsets. In this paper, an in-orbit TH validation and correction algorithm is developed for OMS-L based on the vertical structure of ultraviolet limb-scattered radiance (LSR) profiles. The knee of the LSR profile at 305 nm is employed as an equivalent TH reference, enabling rapid determination and correction of TH offsets. Sensitivity analysis indicates that the algorithm accuracy is within ±300 m, and the impact of algorithm uncertainty on the 320-nm LSR simulations and the ozone profile retrievals is within ±4% and ±8%, respectively. The above algorithm is applied to OMS-L TH data from November 2024 to March 2025. The results show that OMS-L TH offsets generally remain within ±1 km. After TH correction, the LSR simulations show better agreement with the measurements, with a correlation coefficient of 0.973.

The Visible and Infrared Radiometer (VIRR) onboard China’s Fengyun-3A/B/C (FY-3A/B/C) satellites has delivered essential global Earth observations for over 15 years, enabling critical applications in cloud dynamics research, vegetation assessment, and environmental monitoring. However, VIRR lacks onboard calibration systems for its visible/near-infrared channels, which results in progressive radiometric degradation due to cumulative space radiation and detector aging, challenging the generation of stable long-term climate datasets [e.g., the fundamental climate data record (FCDR)]. By integrating simultaneous nadir overpass (SNO) cross-calibration technique with references from Aqua’s Moderate Resolution Imaging Spectroradiometer (MODIS), we identified pronounced seasonal fluctuations in long-term recalibration coefficients, particularly for the 0.86 μm. To isolate these effects, singular spectrum analysis (SSA) was used to decompose the coefficient series into three components: trend, seasonal fluctuations, and residuals. A hybrid calibration model was then formulated by integrating the isolated trend and seasonal features. Validation across globally distributed pseudo-invariant sites confirmed enhanced radiometric stability. The work highlights the necessity of accounting for seasonally modulated calibration artifacts, which were previously unaddressed in operational protocols, to ensure the stability and accuracy of climate data records (CDRs).