## 3 RS Applications in Ocean
### Ocean Tide (OT)
#### 3.5.3 SAR  
SAR data have also been utilized for waterline extraction, which is an important step for studying tidal flats. This can be performed through measuring the roughness of the surface based on the differences in surface roughness between the smooth tidal flats and the water surface [287]. Thus, an efficient edge detection method should be applied to delineate the border between open water and tidal flats [288]. For instance, [PERSON] et al. [288] obtained the border between tidal flats and adjacent water areas by applying a multiscale edge detection algorithm using ERS-2 images. To this end, they used the computationally efficient wavelet transform method in combination with a segmentation algorithm. Additionally, SAR data are the most popular RS resources for studying tidal currents. Thus, different SAR methods, such as radar Line of Sight (LOS), Fourier transformed images, and interferometry, have been so far implemented for tidal current studies. The components and variations of tidal currents can be found in the radar LOS [269]. Moreover, along-track InSAR has been widely applied to monitor surface tidal currents [289]. To this end, ocean waves are detected using SAR and transfer functions applied to the image spectra. Furthermore, Doppler measurements by the along-track interferometry of two SAR images can retrieve surface currents. For this purpose, phase differences between coregistered pixels of two images are obtained using the signal phase [269; 289]. The phase difference is transferred into LOS scatterer velocity, and then the average effect of the horizontal wave motion is subtracted from the current field [269]. Moreover, tidal currents are mapped using equations including angular frequency, acceleration of gravity, two-dimension wave number, water depth, and the surface current [270]. MCC is another method for tidal current mapping using SAR data. Since this method cannot address the large spatiotemporal variations in a typical diurnal or semidiurnal tidal current, temporal decorrelation is minimized by a virtual SAR constellation data pair [290]. InSAR has also been used for OTL studies. Due to small changes caused by OTL, InSAR techniques are the most common RS methods for OTL studies. However, it is challenging to distinguish the OTL effects from similar signals in Differential InSAR (DInSAR) measurements. Since existing tools readily calculate the OTL effect, the OTL prediction model should be subtracted from an interferogram before tectonic analysis [291]. The dominant component of OTL displacement is vertical, and the LOS look angle of most SAR satellites makes them sensitive to vertical-ground deformation [291]. The proposed methods first accurately remove the orbit errors under the constraint of the relative displacements of the GPS PPP solutions in the LOS direction. Then, the crustal deformations caused by the OTL in DInSAR interferograms are analyzed. Finally, the OT model is applied to correct the OTL effect in the DInSAR interferograms [292]. Many studies have investigated the applications of the DInSAR technique for OTL analysis. For example, [PERSON] and [PERSON] [291] investigated the capability of OTL correction in DInSAR using an empirical OT model to illustrate the superiority of an OT model in correcting the OTLeffect in DInSAR results. The focus was on displacements from mass loading due to the OT to study processes occurring using ERS and ENVISAT data. Additionally, [PERSON] et al. [292] measured the OTL effect as a potential error source exploiting DInSAR data and tried to use empirical models to correct the error. They proposed a linear surface model to correct the relative displacements of the GPS PPP in LOS over the Los Angeles basin. Then, an OT model was applied to correct the OTL effect in the DInSAR interferograms. It was observed that the bilinear ramp function model was in agreement with the experimental results. Finally, multitemporal SAR data have been extensively used for tidal wetland mapping [293; 294; 295; 273]. For instance, [PERSON] et al.