Modeling the satellite instrument visibility range for detecting underwater targets

To assess the ability of a satellite instrument to detect submerged targets, we constructed a semi-analytical relationship to link target reflectance and the contrast threshold of the satellite instrument to visibility ranges. Using numerical simulation, we found that the contrast threshold of the satellite instrument was equal to 50 % of the residual error contained in satellite R_rs data. We evaluated our model using known sea depths of optically shallow water and found that the model produced ∼ 16 % uncertainty in retrieving the visibility range around the edge of the optically shallow water. By comparison, the contrast threshold of the human eye was more than 20 times larger than the satellite instrument contrast threshold. In addition, using a Secchi disk submerged in the shallow water, we found that the Secchi disk was invisible to the human eye when the disk was still visible to a high-quality camera handheld or mounted on an unmanned aerial vehicle. Moreover, when the image data quality was as well as MODIS instrument, we found that the maximum instrument visibility range reached 130 m in theory, which was approximately four times larger than the maximum reached by the human eye. Our findings suggest that high-quality cameras such as satellite instruments are more effective than the human eye for detecting underwater targets.