Low Altitude Coastal Aerial Photogrammetry for High-Resolution Seabed Imaging and Habitat Mapping of the Shallow Areas

摘要

This paper explores the application of Kite Aerial Photography at the coastal environment along with digital photogrammetry for seabed geomorphological mapping. The procedure of acquisition, processing and interpretation of kite aerial imagery from the sub-littoral zone up to 5 meters depth is analysed. Using a calibrated non-metric digital compact camera we managed to acquire several near-vertical aerial images from two neighboring coastal sites in the Attica Peninsula (Greece). Both sites express significant geomorphological variability and they have a relatively smooth slope profile. For the photogrammetric processing topographic and bathymetric survey simultaneously with Kite Aerial Photography using a portable DGPS of sub-meter accuracy are acquired. Processing steps included the interior and exterior orientation as well as ortho-rectification of images. This produced final orthomosaics for each site, at approximately 1:500 scales, with spatial resolution of a few centimeters. Interpretation of the seabed was based on colour and texture features of certain areas with explicit seabed reflectivity and was supported by underwater photographs for ground truthing. At the final stage of image analysis, the boundaries (contrasting reflectivity) between different bottom types were recognised and were digitised as 2D objects using GIS. Concluding, this project emphasizes on the advantages and physical restrictions of Kite Aerial Photography in mapping small-scale geomorphological features in shallow water environments with accepted water clarity. Furthermore, this study appoints the suitability of the KAP method for mapping shallow water habitats such as soft/hard substrates, coastal reefs and sea grass meadows. Consequently, the application of low altitude digital photogrammetry is proposed for shallow water surveying as an alternative or supplementary to the side scan sonar and backscatter recorder until a maximum depth of 10 meters, along with certain improvements.