Abstract
The automatic detection and analysis of ocean eddies has become a popular research topic in physical oceanography during the last few decades. Compact polarimetric synthetic aperture radar (CP SAR), an emerging polarimetric SAR system, can simultaneously acquire richer polarization information of the target and achieve large bandwidth observations. It has inherent advantages in ocean observation and is bound to become an ideal data source for ocean eddy observation and research. In this study, we simulated the CP data with L-band ALOS PALSAR fully polarimetric data. We assessed the detection and classification potential of ocean eddies from CP SAR by analyzing 50 CP features for 2 types of ocean eddies (“black”and “white”) based on the Euclidean distance and further carried out eddy detection and eddy information extraction experiments. The results showed that among the 50 CP features, the dihedral component power (Pd), shannon entropy (SEI), double bounce (Dbl), Stokes parameters (g0 and g3), eigenvalue (l1), lambda, RVoG parameter (ms), shannon entropy (SE), surface scattering component (Ps), and σHH all performed better for detecting “white” eddies. Moreover, the H-A combination parameter (1mHA), entropy, shannon entropy (SEP, SEI, and SE), probability (p2), polarization degree (m), anisotropy, probability (p1), double bounce (Dbl), H-A combination parameter (H1mA), circular polarization ratio (CPR), and σVV were better CP features for detecting “black” eddies.
Highlights
Ocean eddies represent an important ocean phenomenon, affecting both surface currents and the transportation of chemical substances, which play a significant role in theocean circulation structure and marine ecology
The above features are used for white eddies (W-E) extraction, and it should be noted that since the detection of W-E is mainly to identify bright bands generated by wave–current interaction, only the edges of W-E are discussed
The intensity of E with diameters of km (E-1) was relatively large, and the roughness of the sea surface caused by wave–current interaction was greater, which resulted in a larger difference in the backscattering between the eddy edge and the ocean background, having a relatively good detection result
Summary
Ocean eddies represent an important ocean phenomenon, affecting both surface currents and the transportation of chemical substances, which play a significant role in theocean circulation structure and marine ecology. Ocean eddies affect atmospheric phenomena, such as wind, clouds, and rainfall through air–sea interactions [1,2]. Tracking and observing eddies has become one of the most critical advances in ocean remote sensing in the 21st century. Since ocean eddies were first discovered in the 1970s, the observation of mesoscale eddies has primarily relied on dynamic sea surface height data obtained from satellite. 2021, 13, 4905 altimeters to retrieve and track eddies [5,6]. Owing to the low spatial resolution of traditional satellite altimeter data, it is difficult to detect sub-mesoscale eddies and small-scale eddies ranging from 1 to 100 km, severely restricting eddies’ identification [7]
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