REFLECTIVE SPECTROSCOPY OF OTTAWA SAND, UREA, AND METHYLENE BLUE: A PROOF-OF-CONCEPT STUDY TOWARD DEVELOPING HYPERSPECTRAL REMOTE SENSING / IMAGE SPECTROSCOPY CAPABILITIES FOR HUMAN WASTE INVESTIGATIONS

Human urine is of significant interest to forensic studies. The detection of urine in outdoor environments by hyperspectral remote sensing / image spectroscopy (HRS/IS) could be a valuable capability for supporting crime scene investigations, search and rescue efforts, and monitoring releases of human waste. Urea is a major component of human urine. Methylene blue (MB) is a well-studied distinctive compound that can be used as a pharmaceutical and is excreted essentially unmodified in urine. This study investigated combination experiments using purchased Ottawa sand, urea, urea solutions, and MB solutions to assess the detection and spectral behavior of these materials. Sand and liquid combinations were analyzed using an ASD FieldSpec 4 High Resolution spectroradiometer with a contact probe. Analytical work on Ottawa sand including SEM and light microscopy analysis aid in better interpreting combination experiments and indicate minor Fe-oxides, glass inclusions, and fluid inclusions are common and influence the spectra of Ottawa Sand. Infrared spectroscopy studies of urea and solutions are common, however, reflected spectroscopy (350 – 2500 nm) investigations are less common. Bond assignments for some major reflective features of urea are found to be ~1160 nm (C=O, fourth overtone); ~1460 nm (symmetric N-H stretch, first overtone); ~1520 nm (N-H stretch, first overtone); ~1990 nm (N-H stretch and N-H bend combination), ~2030 nm (C=O stretch second overtone); ~2070 nm (N-H deformation and overtone); ~2180 nm (N-H bend, C=O stretch, C-N stretch); ~2300 nm (N-H stretch and C=O stretch). Solutions of urea had limited detection on Ottawa sand and crystalline urea could be detected routinely for most conditions. MB has a reasonably distinct reflective spectra and can be detected at all experimental conditions. The behavior of MB opens questions regarding the behavior of other pharmaceuticals and if they may effectively trace human urine using HRS/IS. Results from this study should support global HRS/IS efforts for searching for missing persons. Specific contexts include outdoor habitation sites, trails, and human trafficking sites. IS of indoor crime scenes would also benefit from this data. Results may also support HRS/IS monitoring of refugee camps and disaster sites.