On the Performance of the MPI Algorithm for the Retrieval of Significant Wave Height From ERS Synthetic Aperture Radar

2003 ◽  
Author(s):  
Nelson Violante-Carvalho ◽  
Ian S. Robinson
Keyword(s):  
Synthetic Aperture Radar ◽  
Wave Height ◽  
Significant Wave Height ◽  
Synthetic Aperture ◽  
Wave Spectra ◽  
Sar Images ◽  
Significant Wave ◽  
Directional Wave ◽  
Better Than ◽  
Aperture Radar

Spaceborne Synthetic Aperture Radar (SAR) is to date the only source of two dimensional directional wave spectra with continuous and global coverage when operated in the so-called SAR Wave Mode (SWM). Since the launch in 1991 of the first European Remote Sensing Satellite ERS-1 and more recently with ENVISAT millions of SWM imagettes containing detailed spectral information are now available in quasi-real time. This huge amount of directional wave data has opened up many exciting possibilities for the improvement of our knowledge of the dynamics of ocean waves. However the retrieval of wave spectra from SAR images is not a trivial exercise due to the nonlinearities involved in the mapping mechanism. The Max-Planck Institut (MPI) scheme was the first ever proposed and most widely used algorithm to retrieve directional wave spectra from SAR images. In this work significant wave height retrieved from SAR images using the MPI scheme are compared against one year of directional buoy measurements obtained in deep water and against WAM spectra. Our results show that for periods shorter than 12 seconds the WAM model performs better than the MPI method, even considering the fact that the model is used as first guess to the MPI scheme. However, for periods longer than 12 seconds (the part of the spectrum directly observed by SAR) the MPI method performs better than WAM. This is in contrast with the results obtained by Voorrips et al. (2001), who found that the performance of the WAM model is superior even when only the low wavenumber part of the spectrum is considered.

scholarly journals An Empirical Algorithm to Retrieve Significant Wave Height from Sentinel-1 Synthetic Aperture Radar Imagery Collected under Cyclonic Conditions

2018 ◽  
Vol 10 (9) ◽  
pp. 1367 ◽  
Author(s):  
Weizeng Shao ◽  
Yuyi Hu ◽  
Jingsong Yang ◽  
Ferdinando Nunziata ◽  
Jian Sun ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Wave Height ◽  
Significant Wave Height ◽  
Synthetic Aperture ◽  
Training Dataset ◽  
Sar Images ◽  
Data Set ◽  
Significant Wave ◽  
Sar Imagery ◽  
Aperture Radar

In this study, an empirical algorithm is proposed to retrieve significant wave height (SWH) from dual-polarization Sentinel-1 (S-1) synthetic aperture radar (SAR) imagery collected under cyclonic conditions. The retrieval scheme is based on the well-known CWAVE empirical function that is here updated to deal with multi-polarization S-1 SAR measurements collected using the interferometric wide (IW) and the Extra Wide-Swath (EW) imaging modes, under cyclonic conditions. First, a training dataset that consists of six S-1 SAR images collected under cyclonic conditions is exploited to both tune the retrieval function and to check the soundness of the retrievals against the co-located WAVEWATCH-III (WW3) numerical simulations. The comparison of simulation from the WW3 model and measurements from altimeter Jason-2 shows a 0.29m root mean square error (RMSE) of significant wave height (SWH). Then, a testing data-set that consists of two S-1 SAR images is exploited to provide a preliminary validation. The results, verified against both WW3 and European Centre for Medium-Range Weather Forecasts (ECMWF) data, show the soundness of the herein approach.

scholarly journals On the retrieval of significant wave heights from spaceborne Synthetic Aperture Radar (ERS-SAR) using the Max-Planck Institut (MPI) algorithm

2005 ◽  
Vol 77 (4) ◽  
pp. 745-755 ◽  
Author(s):  
Nelson Violante-Carvalho
Keyword(s):  
Data Assimilation ◽  
Synthetic Aperture Radar ◽  
Synthetic Aperture ◽  
Wave Spectra ◽  
Max Planck ◽  
Sar Images ◽  
Significant Wave ◽  
Wave Heights ◽  
Significant Wave Heights ◽  
Directional Wave

Synthetic Aperture Radar (SAR) onboard satellites is the only source of directional wave spectra with continuous and global coverage. Millions of SAR Wave Mode (SWM) imagettes have been acquired since the launch in the early 1990's of the first European Remote Sensing Satellite ERS-1 and its successors ERS-2 and ENVISAT, which has opened up many possibilities specially for wave data assimilation purposes. The main aim of data assimilation is to improve the forecasting introducing available observations into the modeling procedures in order to minimize the differences between model estimates and measurements. However there are limitations in the retrieval of the directional spectrum from SAR images due to nonlinearities in the mapping mechanism. The Max-Planck Institut (MPI) scheme, the first proposed and most widely used algorithm to retrieve directional wave spectra from SAR images, is employed to compare significant wave heights retrieved from ERS-1 SAR against buoy measurements and against the WAM wave model. It is shown that for periods shorter than 12 seconds the WAM model performs better than the MPI, despite the fact that the model is used as first guess to the MPI method, that is the retrieval is deteriorating the first guess. For periods longer than 12 seconds, the part of the spectrum that is directly measured by SAR, the performance of the MPI scheme is at least as good as the WAM model.

scholarly journals Deep Learning for Predicting Significant Wave Height From Synthetic Aperture Radar

2020 ◽  
pp. 1-9
Author(s):  
Brandon Quach ◽  
Yannik Glaser ◽  
Justin Edward Stopa ◽  
Alexis Aurelien Mouche ◽  
Peter Sadowski
Keyword(s):  
Deep Learning ◽  
Synthetic Aperture Radar ◽  
Wave Height ◽  
Significant Wave Height ◽  
Synthetic Aperture ◽  
Significant Wave ◽  
Aperture Radar

scholarly journals The Influence of Air–Sea Roughness, Sea Spray, and Storm Translation Speed on Waves in North Atlantic Storms

2008 ◽  
Vol 38 (4) ◽  
pp. 817-839 ◽  
Author(s):  
Weiqing Zhang ◽  
William Perrie
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Storm Track ◽  
Wave Drag ◽  
Sea Spray ◽  
Wave Spectra ◽  
Translation Speed ◽  
Significant Wave ◽  
Directional Wave ◽  
The Impact

Abstract A coupled atmosphere–wave–sea spray model system is used to evaluate the impact of sea spray and wave drag on storm-generated waves, their height variations, and directional wave spectra in relation to the storm location and translation speed. Results suggest that the decrease or increase of significant wave height due to spray and wave drag is most significant in high-wind regions to the right of the storm track. These processes are modulations on the maximum-wave region and tend to occur several hours after the peak wind events, depending on the storm translation velocity. The translation speed of the storm is important. The directional variation between local winds and wind-generated waves within rapidly moving storms that outrun the waves is notably different from that of trapped waves, when the dominant waves’ group velocity approximates the storm translation speed. While wave drag and spray can increase or reduce the magnitudes of wind and significant wave height, their nondirectional formulations allow them to have little apparent effect on the directional wave spectra.

Extreme Waves Detected by Satellite Borne Synthetic Aperture Radar

2002 ◽  
Author(s):  
Susanne Lehner ◽  
Johannes Schulz-Stellenfleth ◽  
Andreas Niedermeier ◽  
Jochen Horstmann ◽  
Wolfgang Rosenthal
Keyword(s):  
Synthetic Aperture Radar ◽  
Wave Height ◽  
Sampling Rate ◽  
Ocean Wave ◽  
Synthetic Aperture ◽  
Extreme Waves ◽  
Sar Images ◽  
Data Set ◽  
Sar Data ◽  
Aperture Radar

Within the last 20 years at least 200 supercarriers have been lost, due to severe weather conditions. In many cases the cause of accidents is believed to be ‘rouge waves’, which are individual waves of exceptional wave height or abnormal shape. I situ measurements of extreme waves are scarce and most observations are reported by ship masters after the encounter. In this paper a global set of synthetic aperture radar (SAR) images is used to detect extreme ocean wave events. The data were acquired aboard the European remote sensing satellite ERS-2 every 200 km along the track. As the data are not available as a standard product of the Europea Space Agency (ESA), the radar raw data were focused to complex SAR images using the processor BSAR developed by the German Aerospace Center. The entire SAR data set covers 27 days representing 34000 SAR imagettes with a size of 5km×10km. Complex SAR data contain information on ocean wave height, propagation direction and grouping as well as on ocean surface winds. Combining all of this information allows to extract and locate extreme waves from complex SAR images on a global basis. Special algorithms have been developed to retrieve the following parameters from the SAR data: Wind speed and direction, significant wave height, wave direction, wave groups and their individual heights. The satellite ENVISAT launched in March 2002 acquires SAR data with an even higher sampling rate (every 100 km). It is expected that a long-term analysis of ERS and ENVISAT data will give new insight into the physical processes responsible for rogue wave generation. Furthermore, the identification of hot spots will contribute to the optimization of ship routes.

Study on Wave Spectra in South Coastal Waters of Jiangsu

2012 ◽  
Vol 212-213 ◽  
pp. 193-200 ◽  
Author(s):  
Wei Bin Feng ◽  
Bin Yang ◽  
Hai Jing Cao ◽  
Xing Ye Ni
Keyword(s):  
Wave Height ◽  
Water Waves ◽  
Significant Wave Height ◽  
Spectral Characteristics ◽  
Peak Frequency ◽  
Spectral Peak ◽  
Wave Spectra ◽  
Spectral Parameters ◽  
Significant Wave ◽  
Better Than

The paper examined the spectral characteristics of shallow water waves, which was based on the wave data collected along the south coast of Jiangsu. It proposes a tentative spectra model which can work better than Joint North Sea Wave Project (JONSWAP)spectra. Both of the value of tentative spectral parameters (α and γ) increase with significant wave height and spectral peak frequency. According to a regression analysis, empirical equations are achieved, which is related to the parameters with significant wave height and spectral peak frequency. The study shows that the measured wave spectra can be represented by tentative spectra, and the fitting results in high-frequency tail of tentative spectra are better than that of JONSWAP spectrum with modified parameters.

scholarly journals Evaluation of the Significant Wave Height Data Quality for the Sentinel-3 Synthetic Aperture Radar Altimeter

2020 ◽  
Vol 12 (18) ◽  
pp. 3107
Author(s):  
Yong Wan ◽  
Rongjuan Zhang ◽  
Xiaodong Pan ◽  
Chenqing Fan ◽  
Yongshou Dai
Keyword(s):  
Synthetic Aperture Radar ◽  
Data Quality ◽  
Wave Height ◽  
Water Depth ◽  
Deep Water ◽  
Significant Wave Height ◽  
Synthetic Aperture ◽  
Radar Altimeter ◽  
Significant Wave ◽  
Water Depths

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.

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