# Study on the Elimination Method of Wind Field Influence in Retrieving a Sea Surface Current Field
###### Abstract  
An along-the-track interferometric synthetic aperture radar (ATI-SAR) system can estimate the radial velocity of a moving target on the ground and on a sea surface current. This acquires the interference phase by combining two composite SAR images obtained by two antennas spatially separated along the direction of movement of the platform. The key to retrieving the sea surface current is to remove the interference of sea surface waves, wind-generated current, and Bragg phase velocity in the interference Doppler velocity. Previous methods removed the surface waves, Bragg phase velocity, and other interferences based on externally-assisted wind fields (e.g., ECMWF), using the M4S or other models. However, the wind fields obtained from ECMWF and other external information are often average results of a large temporal and spatial scale, while the images obtained from SAR are high-resolution images of sea surface transients, which are quite different in time and space. This paper takes the SAR image data of the Gaofen-3 satellite as the research object and employs an SAR-based wind field retrieval method to obtain an SAR-observed transient wind field. Combined with the CDOP model, the interference of Doppler velocities, such as the sea surface wave, wind-generated current, and Bragg wave phase velocity, was calculated and subtracted from the Doppler velocity, to obtain the sea surface velocity result. Then, the current field measured by the shore-based HF radar was compared with that obtained by correcting the ATI Doppler velocity based on the SAR retrieved wind field and the ECMWF wind field. The comparison of results indicated that the wind field correction result based on the SAR retrieved wind field was closer to the current field measured by the shore-based HF radar than the wind field correction result based on the ECMWF wind field. sea surface current; along-track interferometric SAR; Gaofen-3 satellite; CDOP model 202  
on space-borne SAR concerns ocean interpretation and qualitative comparison of ocean currents to verify its ability to detect various ocean physical phenomena [3] (such as ocean fronts, eddies, internal waves, etc.). Currently, two techniques can be adopted to achieve current field inversion based on SAR: doppler centroid analysis (DCA) and along-track interferometric (ATI). Both can obtain the radial velocity in the current field. The DCA-based currents are less accurate than the ATI-based ones, but close to short-baseline ATI can produce quality results; meanwhile, DCA is an alternative to divided-antenna mode ATI, and the results demonstrate the true potential of the ATI technique at near-optimum baselines [4]. Along-track interferometric synthetic aperture radar (ATI-SAR) has the unique ability to measure sea surface velocity. In 1987, [PERSON] and [PERSON] [5] of NASA's Jet Propulsion Laboratory first proposed the method of using ATI to measure high-resolution sea currents, and its feasibility was verified through experiments. [PERSON] et al. [6; 7] used two L-band radar antennas to investigate the measurement of tidal current at the outlet of the Gulf, and two antennas were installed on an aircraft. This was the first feasibility study. In addition, the ability of ATI-SAR to measure surface velocity was demonstrated by [PERSON], [PERSON], and others through several studies with airborne radar. The fundamental concept for measuring surface velocity is that the phases of two complex SAR images obtained from the same scene and the same antenna have a short time delay, and the phase difference is proportional to the line-of-sight velocity of the target [8; 9]. The theoretical background and numerical model of ATI-SAR are presented in [8]. Meanwhile, many experiments on different platforms have been conducted to validate ATI technologies, such as airborne, space shuttle, and satellite [9; 10; 11]. The first study based on bistatic TanDEM-X (TDX) was reported in [13].