A Study on the Delineation of Coral Reefs in Andaman and Lakshadweep Islands Using RISAT-1 Data

Synthetic Aperture Radar (SAR) for Ocean: A Review

“…Yet, they are very vulnerable to coastal development and water quality degradation [131]. Although most of the studies about aquatic vegetation and coral reef mapping and monitoring using satellite data have focused on multispectral imagery [132], a significant correlation has been proved between the SAR backscattering coefficient and both above-water dry biomass and height of the plants [19]. SAR data can be utilized for mapping coral reef and underwater plants, depending on the sea state and acquisition quality [19], [133].…”

“…10 demonstrates the distribution of different salt marsh samples from SAR features in (a) Yellow River Estuary and (b) Yangtze River Estuary [134]. Coral reef and aquatic vegetation are indirectly detectable in SAR images due to the interaction of the water currents with the underwater features, which modulates the sea surface roughness and the interaction of the radar wave with the sea surface [19], [133]. Most of the studies on aquatic vegetation monitoring through SAR data combined field campaign data with SAR backscattering coefficient to map above-and underwater plants to obtain a better accuracy [135].…”

“…Most of the studies on aquatic vegetation monitoring through SAR data combined field campaign data with SAR backscattering coefficient to map above-and underwater plants to obtain a better accuracy [135]. Various supervised and unsupervised classification algorithms have also been used for aquatic vegetation mapping from SAR images [19], [135]. For instance, Nair et al [19] investigated the applicability of RISAT-1 SAR images for coral reefs mapping in Andaman and Lakshadweep Islands in the Indian Ocean.…”

“…Various supervised and unsupervised classification algorithms have also been used for aquatic vegetation mapping from SAR images [19], [135]. For instance, Nair et al [19] investigated the applicability of RISAT-1 SAR images for coral reefs mapping in Andaman and Lakshadweep Islands in the Indian Ocean. Preprocessing steps, including the land mask and speckle filtering, were applied to the dual-polarized georeferenced RISAT-1 SAR images.…”

“…Optical and LiDAR data are the most frequently used satellite data for aquatic vegetation studies [132], [240]; however, SAR systems are also proved to be very useful for deriving information about the plant structure and physical properties, especially over shallow waters [241]. Moreover, the ability of SAR systems to detect underwater topography, due to the sea surface roughness variations, is helpful for underwater vegetation monitoring [19]. However, the detectability of above/under water vegetation on SAR images is heavily influenced by the incident angle [137].…”