Spectral indices for enhancing aquatic vegetation: a case study of seaweed on the Arabian coast of Pakistan using Worldview-2 data

Abstract

ABSTRACT This study assessed the performance of widely used aquatic vegetation indices and introduced a novel index – the normalized difference aquatic vegetation enhancing index (NDAVEI). The NDAVEI was used to map seaweed resources in Pakistan along the 1,050 km long Karachi coast, and the results were compared with those obtained from other vegetation indices. Due to their widespread use in food, cosmetics and industrial goods, seaweed resources have great economic potential. They also play a significant role in aquaculture and fish breeding. Many sea species rely on seaweeds for their shelter and food requirements. The conservation of marine biodiversity needs seaweeds’ systematic monitoring and mapping to maintain the dependent species’ vital biological associations. Despite rich seaweed stock, these resources remain largely unmapped in Pakistan. Given these precious coastal resources’ significant economic and ecological importance, there is a pressing need to preserve and map seaweed sites in Pakistan. Traditionally, marine scientists have used sampling methods to describe shallow intertidal water marine habitats, but these methods are time intensive. Remote sensing (RS) data and geographical information system (GIS) tools are efficient and less time-consuming for mapping and classifying marine resources. This study compared the effectiveness of commonly used indices and NDAVEI to extract and map seaweed resources using high-resolution WorldView-2 satellite data. The results were verified through site observations. The NDAVEI can potentially improve the effectiveness and efficiency of seaweed mapping efforts. When combined with object-based image analysis (OBIA), it provides more precise area estimation than other indices.