Estimation of error in large area underwater photomosaics using vehicle navigation data

Creating geometrically accurate photomosaics of underwater sites using images collected from an AUV or ROV is a difficult task due to dimensional errors which grow as a function of 3D image distortion and the mosaicking process. Although photomosiacs are accurate locally their utility for accurately representing a large survey area is jeopardized by this error growth. Evaluating the error in a mosaic is the first step in creating globally accurate photomosaics of an unstructured environment with bounded error. Using vehicle navigation data and sensor offsets it is possible to estimate the error present in large area photomosaics independent of the mosaic construction method. This paper presents a study of the error sources and an estimation of the error growth across an underwater photomosaic. World coordinate locations of the individual image centers are projected into the image coordinate space of the mosaic. The spatial error is then shown as the divergence between the position of the corresponding image centers in the mosaic and the positions determined by the navigation projection. Accurate world coordinate system position estimates of the image centers are obtained from the on board navigation sensors and the EXACT acoustic navigation system. Several large area mosaics using imagery collected by the JASON ROV are shown as examples.