Abstract: To evaluate the observational performance and applicability of different significant wave height products from SWIM (Surface Waves Investigation and Monitoring) onboard CFOSAT (China-France Oceanography Satellite) over the Northwest Pacific Ocean, this study constructs spatiotemporally matched datasets for five categories of SWH (significant wave height) products, including nadir, 6°, 8°, 10° off-nadir beams and combined wave spectrum products, using drifting buoy observations from the Japan Meteorological Agency spanning 2019 to 2024. Correlation coefficient, RMSE (root mean square error), mean BIAS and scatter index are used to systematically assess retrieval accuracy. The results show that the five SWIM products are highly consistent with buoy measurements. All correlation coefficients exceed 0.96, and the RMSE ranges from 0.298 m to 0.324 m, demonstrating high overall retrieval precision. The 10° off-nadir beam product delivers the best performance, with an SWH RMSE of 0.298 m and a BIAS of 0.107 m. Measurement errors generally increase with growing sea state. The discrepancies among different products are relatively small under moderate and low sea states, and the nadir product has the lowest accuracy among them. In contrast, the nadir product exhibits the smallest error under high sea states, with an RMSE of 0.45 m. There is a trade-off between accuracy and spatial coverage for different products. The 10° beam achieves the optimal stability and precision, while the combined wave spectrum product has the maximum number of matched samples. This study indicates that different observation geometries of CFOSAT SWIM exert systematic effects on wave retrieval accuracy. Off-nadir beam observations are generally superior to nadir measurements, and the 10° beam presents the best comprehensive performance in the Northwest Pacific Ocean.

Key words: Significant wave height (SWH), China-France Oceanography Satellite (CFOSAT), SWIM spectrometer, Drifting buoy, Northwestern Pacific