APPLICATION OF SIDE SCAN SONAR TECHNOLOGY TO FORENSIC RECOVERY OF HUMAN REMAINS IN UNDERWATER ENVIRONMENTS

This study evaluated the effectiveness of side scan sonar (SSS) technology in identifying submerged human remains in various underwater sediment facies. This application offers improvements in search efficiency and coverage when compared to deploying a traditional dive team. Impedance values from the literature were used to calculate reflection coefficients (R) between seawater and 1) sediments of different grain sizes and 2) targets of forensic interest.

Two locations with differing grain sizes were chosen in the North River (Salem, MA). This field site was chosen due to its close proximity to campus, diverse sediment types, and surrounding geography and urban infrastructure that could potentially allow for illicit criminal activities such as body dumping. A 200 kHz (SyQwest AquaScan SSS System) base scan was conducted using gridded parallel transects (area = 0.22 km²), followed by secondary data collection of targets deployed in two locations. A 115kg, 0.9m long domestic pig (Sus scrofa domesticus) was used as a human body analog and was locally sourced ~12 hours before deployment. To mimic the shape of a human body, a 1.8m plastic mannequin was also deployed. To sink the targets, the mannequin was filled with sand and both the mannequin and the pig were harnessed to concrete blocks. Each target was scanned a minimum of 4 times in each location, with each approach being orthogonal to the last. The highest image quality was achieved when the vessel traveled perpendicular to the body axis. The system settings for this imaging included a 20-meter range with a gain setting of 8 dB. Additionally, a 40-meter range was used for the base scan with a gain setting of 18 dB, while a gain setting of 8 dB was applied for the 40-meter scans of the target objects to serve as comparison. The 20-meter range provided accurate reflections of the target objects relative to the surrounding sediment, but the shapes of the objects were less clearly defined. In contrast, the 40-meter range sonar imaging provided well-defined shapes of the target objects but did not accurately represent the target objects’ reflections due to sonar absorption caused by the surrounding sediment type.