Evaluation of SWOT Level 3 Sea Surface Height Data

The SWOT satellite was launched in December 2022 and employs a novel SAR-in technology to achieve high-precision measurements over inland waters and the ocean. For ocean observations, SWOT provides low-rate data products, referred to as LR data. Currently, the mainstream post-processed LR products are released at Level-3 (L3). However, the accuracy level of the SWOT L3 data still requires comprehensive evaluation and analysis. This study primarily focuses on the assessment of SWOT SSH data in both coastal regions and the open ocean.

First, a crossover analysis was conducted using 2-km spatial resolution data over the open ocean and coastal areas. The results indicate that the mean and standard deviation of SSH crossover differences from SWOT are consistent with the accuracy levels of conventional satellite altimetry missions. Second, in situ tide gauge observations were used to evaluate SWOT L3 SSH data with spatial resolutions of 2 km and 250 m within 20 km of the coastline. The results demonstrate good correlation between SWOT L3 data at both resolutions and tide gauge measurements. However, at certain stations—such as those located in regions with complex nearshore bathymetry or around islands and atolls—the correlations are relatively lower.

In addition, an evaluation was performed for SWOT L3 data across different cross-track distance ranges. The results similarly show that, provided valid data are available, SWOT L3 SSH data exhibit good correlation with tide gauge observations across various cross-track distances. Both datasets reveal a consistent pattern of degraded data quality toward the swath edges, while relatively higher quality is observed near the nadir region. Furthermore, a statistical analysis of data loss rates within 5 km of the coastline indicates that the average data loss rate reaches approximately 70% for the 2-km resolution data, whereas the 250-m resolution data exhibit an average loss rate of about 31% within the same nearshore zone.

Finally, comprehensive analysis of all results reveals noticeable differences in data quality between the left and right swaths, which may be related to the satellite’s flight attitude. This issue requires further investigation.