Design of spectral indices for the detection of soil pollutants associated with the disappearance of persons: The case of Mexico

Studies on soil contamination detection through remote sensing have so far focused on pollutants from agricultural, mining and industrial activities. However, the extended practice of using chemical substances for the disappearance of people and/or evidence of crimes by criminal organizations can cause soils disturbance and contamination that may be detected through remote sensing methods. This article describes an experiment that simulated soil contamination with substances related to criminal activities. The visible-infrared spectral reflectance of contaminated and non-contaminated areas was measured for six months and measurements were analyzed to design spectral indices involving one, two or three wavebands. The analyzes showed that nine of twelve polluted soils could be detected at least once with at least one index, of which those contaminated with diesel and chlorhydric acid required a hyperspectral resolution (less than 24 nm). Furthermore, by limiting the wavebands to those from 15 commercial satellites and one unmanned aerial vehicle (UAV) camera, we showed that only four substances could be detected using one of the 15 indices with different detection rates, and only the WorldView-3 (WV3) satellite contained the required wavebands to detect these four substances. Some of these multispectral indices were further demonstrated in a couple real-world forensic search areas, indicating a great potential for forensic searches.