The Arctic Ocean presents significant challenges for estimating sea surface wave fields using C-band synthetic aperture radar (SAR) due to the distortion caused by the reflection of sea ice. This article introduces a novel procedure to successfully consider the influence of sea ice in SAR wave retrieval at latitude <80°. A total of 1600 Sentinel-1 (S-1) images, which were acquired in interferometric wide mode in vertical–vertical (VV) and horizontal–horizontal (HH) polarization, were collected. All the S-1 images are collocated with wave simulations from a numerical wave model WAVEWATCH-III (WW3) to expand the evaluation data set for the wave retrieval algorithm. The validation of hindcasting significant wave heights (SWHs) against operational products from the Haiyang-2B (HY-2B) altimeter from January 2021 to April 2021 yields a root-mean-squared error (RMSE) of 0.48 m, a correlation coefficient (COR) of 0.98, and a scatter index (SI) of 0.11. The K-means clustering algorithm was applied to estimate sea ice concentration from the images. Using 1000 images in the training data set, the tilt mapping model transfer functions (MTFs) in VV and HH polarization are generated under various sea ice concentration conditions. Then, a theoretical wave retrieval algorithm, namely, the parameterized first-guess spectrum method, that uses the updated tilt MTF was implemented for an additional 600 images in a test data set for wave retrieval in the Arctic Ocean. Compression of the SAR-derived SWHs and WW3 simulations yields an RMSE of 0.45 m, a COR of 0.91, a bias of 0.38 m, and an SI of 0.11 using the updated tilt MTF, which is an improvement upon the RMSE of 0.60 m, a bias of 0.41 m, a COR of 0.88, and an SI of 0.14 obtained using the previous tilt MTF. Moreover, the accuracy of VV-polarized SAR-derived SWH by using the updated tilt MTF is improved by approximately 0.15-m RMSE and 0.08-m bias, which is based on validating SAR-derived SWHs against the measurements from the HY-2B altimeter. However, the noise in the retrievals still needs further mitigation.
Sea Surface Wave Retrieval From C-Band Sentinel-1 Images in the Arctic Ocean
Migliaccio, Maurizio;Nunziata, Ferdinando;
2025-01-01
Abstract
The Arctic Ocean presents significant challenges for estimating sea surface wave fields using C-band synthetic aperture radar (SAR) due to the distortion caused by the reflection of sea ice. This article introduces a novel procedure to successfully consider the influence of sea ice in SAR wave retrieval at latitude <80°. A total of 1600 Sentinel-1 (S-1) images, which were acquired in interferometric wide mode in vertical–vertical (VV) and horizontal–horizontal (HH) polarization, were collected. All the S-1 images are collocated with wave simulations from a numerical wave model WAVEWATCH-III (WW3) to expand the evaluation data set for the wave retrieval algorithm. The validation of hindcasting significant wave heights (SWHs) against operational products from the Haiyang-2B (HY-2B) altimeter from January 2021 to April 2021 yields a root-mean-squared error (RMSE) of 0.48 m, a correlation coefficient (COR) of 0.98, and a scatter index (SI) of 0.11. The K-means clustering algorithm was applied to estimate sea ice concentration from the images. Using 1000 images in the training data set, the tilt mapping model transfer functions (MTFs) in VV and HH polarization are generated under various sea ice concentration conditions. Then, a theoretical wave retrieval algorithm, namely, the parameterized first-guess spectrum method, that uses the updated tilt MTF was implemented for an additional 600 images in a test data set for wave retrieval in the Arctic Ocean. Compression of the SAR-derived SWHs and WW3 simulations yields an RMSE of 0.45 m, a COR of 0.91, a bias of 0.38 m, and an SI of 0.11 using the updated tilt MTF, which is an improvement upon the RMSE of 0.60 m, a bias of 0.41 m, a COR of 0.88, and an SI of 0.14 obtained using the previous tilt MTF. Moreover, the accuracy of VV-polarized SAR-derived SWH by using the updated tilt MTF is improved by approximately 0.15-m RMSE and 0.08-m bias, which is based on validating SAR-derived SWHs against the measurements from the HY-2B altimeter. However, the noise in the retrievals still needs further mitigation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
