Tide normalized change detection using multitemporal satellite imagery to decipher the turtle rookery dynamics of Gahirmatha, India

A GIS based tide normalized change detection method is developed and tested for analyzing multi-temporal satellite imagery to decipher the morphological change pattern of the two major Olive Ridley sea turtle nesting landforms, namely Ekakula spit and Nasi sandbar situated in the Gahirmatha coast, India. The shoreline position of the coastal landforms at the time of satellite capture is variable as it is dependent on the dynamic nature of the tidal conditions. To normalize the tidal effect, reference Digital Elevation Models (DEM) were constructed from seven-change position of the shoreline, derived from the satellite images sampled between Dec'98 and March'99 under varied tidal conditions. According to the associated tidal levels of the historical images, the corresponding Reference shorelines were extracted from the constructed DEM for quantitative estimation of change in surface area. The methodology has recorded an error up to 4% in the self-consistency check. The ephemeral nature of the rookery was deciphered from the change computation of surface area from the 25 historical images sampled between the years 1988 and 2004 and demonstrated that the geomorphological characteristic of the rookery is one of the major deciding factors for the mass-nesting of the turtles.