Object-oriented extraction of beach morphology from video images

The ARGUS system is a shore-based, optical video system offering a suitable remote sensing technique for the purpose of long-term, high-resolution monitoring of coastal morphodynamics. Ten-minute time-exposure (timex) images obtained by the ARGUS cameras during low tide show the intertidal morphology (bars, troughs and rips) by the differences between water, wet sand and dry sand, where dry sand represents bars, and wet sand and water represent troughs and rips. A semi-automatic object-oriented algorithm was developed for classification of intertidal beach in low-tide video images and was tested on 13 low-tide ARGUS images collected at Noordwijk aan Zee, The Netherlands. Because of the strong relation between the visual observations and object-oriented image analysis, the ARGUS images are subdivided in small homogeneous areas (i.e. objects) by segmentation. Maximum likelihood classification creates a model for each day using a random selection of the objects, which are manually labelled, and their accompanying variables. Of the three classes, class wet sand had a classification fit of 43.4% when compared to an in situ classification; class water was correctly classified for 90.1% and dry sand could be classified best (92.8%). By combining their cross-shore position and their classification, objects can be directly linked with the respective morphological features.