Abstract
Synthetic aperture radar (SAR) altimeters represent a new method of microwave remote sensing for ocean wave observations. The adoption of SAR technology in the azimuthal direction has the advantage of a high resolution. The Sentinel-3 altimeter is the first radar altimeter to acquire global observations in SAR mode; hence, the data quality needs to be assessed before extensively applying these data. The European Space Agency (ESA) evaluates the Sentinel-3 accuracy on a global scale but has yet to perform a detailed analysis in terms of different offshore distances and different water depths. In this paper, Sentinel-3 and Jason-2 significant wave height (SWH) data are matched in both time and space with buoy data from the United States East and West Coasts and the Central Pacific Ocean. The Sentinel-3 SWH data quality is evaluated according to different offshore distances and water depths in comparison with Jason-2 SWH data. In areas more than 50 km offshore, the Sentinel-3 SWH accuracy is generally high and less affected by the water depth and sea conditions (root-mean-square error of 0.28 m and correlation coefficient of 0.98); in areas less than 50 km offshore, the SWH data accuracy is slightly affected by water depth and sea conditions (especially the former). Compared with Jason-2, the observation ability of the Sentinel-3 altimeter in nearshore areas with water depths of 0 m-500 m is greatly improved, but in some deep water areas with stable sea conditions, the Jason-2 SWH data accuracy is higher than that of Sentinel-3. This work provides a reference for the refined application of Sentinel-3 SWH data in offshore deep water areas and nearshore shallow water areas.
Highlights
Waves represent an important dynamic marine process
Yang and Zhang [24] compared the significant wave height (SWH) data of the Sentinel-3 altimeter with the data of National Data Buoy Center (NDBC) buoys in open sea areas and the Jason-3 altimeter in global sea areas; the results showed that the root-mean-square error (RMSE) is 0.2–0.3 m, and the accuracy slightly decreases with increasing SWH data, confirming that Sentinel-3 SWH data have high accuracy
The traditional radar altimeter has the disadvantage of a low resolution, especially in nearshore observations, which are affected by land
Summary
Wave parameters are obtained mainly by the following means: wave buoy observations, wave numerical model predictions, and remote sensing observations, including altimeters, synthetic aperture radar (SAR), and video monitoring. With the introduction of SAR technology in the azimuth direction, radar altimeters have achieved a high resolution and have great potential in the observation of waves and water bodies in areas characterized by complex conditions. The ESA quality evaluation report, which is conducted over a wide spatial range and long period, verifies that the data of the Sentinel-3 altimeter have the advantage of high accuracy; the relationship between the accuracy and factors such as the distance from shore and water depth has not been analyzed in detail. The observation ability of the Sentinel-3 altimeter under different observation conditions has been analyzed, and the advantages of the Sentinel-3 SAR altimeter compared with the traditional Jason-2 altimeter have been verified, thereby providing a basis for specific applications of Sentinel-3 SWH data
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