Practical Differences Between Photogrammetric Bathymetry and Physics-Based Bathymetry

Optical satellite remote sensing (RS) is a time- and cost-effective approach for shallow-water bathymetry over large areas. The photogrammetric and physics-based methods, which do not require
in situ
depth calibration data, are two implementations of RS-based bathymetry. This article compares these two bathymetric methods by using the same WorldView-2 imagery product of a study area in the Xisha Islands of the South China Sea. The focus is to investigate the difference between the resulting depths. The resulted accuracy of the photogrammetric method was slightly higher than that of the physics-based method based on the backward image, but both of them were significantly higher than that of the physics-based method based on the forward image. In the calm clear waters, the resulted depth of the photogrammetric method was closer to the ground truth than that of the physics-based method based on the backward image. In the shoal and adjacent waters where the water was turbid or larger waves were present, the photogrammetric method produced a highly noisy digital depth model (DDM), whereas the physics-based method derived a low-noise DDM from the backward image. In conclusion, the photogrammetric method outperforms the physics-based method in calm clear waters, but the physics-based method performs better than the photogrammetric method in shoal and adjacent waters that has turbid water or waves larger than the image spatial resolution. The photogrammetric DDM is noisier than the physics-based DDM. The accuracy of the physics-based method is also influenced by the non-optimal sun-target-sensor geometry of the images used.