Validation of Sentinel-3A/3B and Jason-3 Altimeter Wind Speeds and Significant Wave Heights Using Buoy and ASCAT Data

Abstract

This study validated wind speed (WS) and significant wave height (SWH) retrievals from the Sentinel-3A/3B and Jason-3 altimeters for the period of data beginning 31 October 2019 (to 18 September 2019 for Jason-3) using moored buoy data and satellite Meteorological Operational Satellite Program (MetOp-A/B) Advanced Scatterometer (ASCAT) data. The spatial and temporal scales of the collocated data were 25 km and 30 min, respectively. The statistical metrics of root mean square error (RMSE), bias, correlation coefficient (R), and scatter index (SI) were used to validate the WS and SWH accuracy. Validation of WS against moored buoy data indicated errors of 1.19 m/s, 1.13 m/s and 1.29 m/s for Sentinel-3A, Sentinel-3B and Jason-3, respectively. The accuracy of Sentinel-3A/3B WS is better than that of Jason-3. All three altimeters underestimated WS slightly in comparison with the buoy data. Errors in WS at different speeds or SWHs increased slightly as WS or SWH increased. Over time, the accuracy of the Jason-3 altimeter-derived WS improved, whereas that of Sentinel-3A showed no temporal dependence. The WSs of the three altimeters were compared with ASCAT wind data for validation purposes over the global ocean without in situ measurements. On average, the WSs of the three altimeters were lower in comparison with the ASCAT data. The accuracy of the three altimeters was found to be consistent and stable at low/medium speeds but it decreased when the WS exceeded 15 m/s. Validations of SWH against buoy wave data indicated that the accuracy of Jason-3 SWH was better than that of Sentinel-3A/3B. However, the accuracy of all three altimeters decreased when the SWH exceeded 4 m. The accuracy of Sentinel-3A and Jason-3 SWH was temporally stable, whereas that of Sentinel-3B SWH improved over time. Analyses of SWH accuracy as a function of wave period showed that the Jason-3 altimeter was better than the Sentinel-3A/3B altimeters for long-period ocean waves. Generally, the accuracy of WS and SWH data derived by the Sentinel-3A/3B and Jason-3 altimeters satisfies their mission requirements. Overall, the accuracy of WS (SWH) derived by Sentinel-3A/3B (Jason-3) is better than that retrieved by Jason-3 (Sentinel-3A/3B).

Ocean Surface Wind Speed Dependence and Retrieval From Off‐Nadir CFOSAT SWIM Data

“…It thus brings the model error and the subsequent bias for the retrieved wind speed. The bias at low winds also appears in wind retrievals from other sensors such as altimeter, SAR, and TRMM PR (Monaldo et al., 2016; Ren et al., 2016; Yang et al., 2020). For this problem, if the approximate wind speed range is known in advance, the bias may be corrected using a separated low wind model.…”

Results of the Dragon 4 Project on New Ocean Remote Sensing Data for Operational Applications

“…Starting with Sentinel-3 performance, the results show that the accuracy of WS and SWH data derived by the Sentinel-3 satisfy their mission requirements. It is found that the accuracy of WS derived from Sentinel-3A/3B is better than that retrieved by Jason-3, while SWH accuracy derived from Jason-3 is better than the one from Sentinel-3A/3B [46]. Sentinel-3A SRAL data quality has been assessed by verifying data availability and monitoring the parameters of altimeter and radiometer through the global statistical analyses of Sentinel-3A Non-Time-Critical (NTC) Marine Level 2 products, in comparison with self-crossovers and cross-calibration with the Jason-3 mission, and the systemic bias of SSH about 2.96 cm shows consistency of the observation between Sentinel-3A SRAL and Jason-3, noting that Sentinel-3A SRAL has good and stable data quality [47].…”

Tropical Cyclone Wind Speed Estimation From Satellite Altimeter‐Derived Ocean Parameters

“…The Pierson-Moskowitz (solid black) line indicates that the majority of the data is in developing seas closely associated with rain. Yang et al (2020) suggested that the accuracy of U 10 reduced when the H S measurement exceeds 4 meters, yet more than half of the data are populated in this state (H S > 5 m). In spite of the H S,Ku depicts many outliers for measurements above 5 m, the H S,C is more consistent with * 10 U even in wet conditions (above the average of W L ).…”

“…Matching criteria with spatial distance of less than 0.25° from the MetOps center pixel to the Jasons point and the temporal difference less than 30 min were applied. Similar criteria were applied by Yang et al (2020) when they validated Jason-3 to MetOps U 10 in normal conditions. This study only accepts the closest MetOps U 10 pixel to the Jasons point to preserve the highly dynamic variation that exists inside the tropical cyclone.…”