Application of PlanetScope-based Depth Invariant Index method in Seagrass Mapping: The study in Thi Nai Lagoon, Binh Dinh Province

Abstract

The seagrass ecosystem is one of the most critical coastal and marine ecologies. The seagrass meadows can protect the seabed coastal erosion, absorb nutrients from coastal runoff and stabilize sediments, act as bio-filters, and provide a habitat for marine animals. Nevertheless, under the impact of socio-economic growth, seagrass in the Thi Nai lagoon has disappeared and been severely deteriorated. Therefore, mapping seagrass in this area is important in informing ecologists and economists to improve sustainable marine ecosystem management strategies. This study aims to detect seagrass in Thi Nai lagoon, Vietnam, by remote sensing method. PlanetScope (PS) satellite images have high spatial (3m) resolution that is applied to extract seagrass using Lyzenga's Depth Invariance Index technique for water column correction and Maximum Likelihood Classifier (MLC). After that, evaluate the accuracy of the results using field data collected from July 29, 2020, to August 1, 2021. The study results achieved high accuracy in isolating seagrass subjects with an overall accuracy of 85.09% and Cohen's Kappa value of 0.8. There are approximately 180 hectares of seagrass in the study area. Moreover, the results also show that seagrasses are mainly distributed on the sand, muddy sand, and sandy mud along the west shore of Thi Nai lagoon and dunes such as Con Chim, Con Trang, and Con Tau, with depths ranging from 1 to 2.5 meters (90.97 %).