Investigating Thermal Infrared Imaging Technology for Passive Marine Mammal Detection

Passive methods to detect the presence of marine mammals in their natural environment are needed. Most current methods involve some level of harassment that results in avoidance behaviors such as course alteration, increased dive time, and group dispersal. This study explored the feasibility of using a thermal infrared imaging (TII) sensor to detect marine mammals. Recent advances in TII technology have enabled the detection of objects of different temperature gradients with portable, reasonably priced camera systems. Although infrared energy does not penetrate water, the heat signature during a surfacing interval may be sufficient for detection of some animals. Under captive conditions, six days of observations were conducted utilizing three models of Raytheon infrared cameras. Comparative observations were made between Florida manatees (Trichechus manatus latirostris), killer whales (Orcinus orca), Pacific whitesided dolphins (Lagenorhynchus obliquidens), bottlenose dolphins (Tursiops truncatus), a juvenile sperm whale (Physeter macrocephalus), California sea lions (Zalophus californianus), and harbor seals (Phoca vitulina). Infrared images were digitally recorded at varying times of day and activity states. Results were highly dependent on the type of TII camera used due to differences in spectral response, sensitivity, image resolution, and lens configurations. Both color and monochrome (black and white) images were obtained, with black-and-white images providing better detection. Images were also affected by length of surface interval, time of dive, and amount of body surface exposed. The portion of the visible range of the electromagnetic spectrum nearest to infrared also impacted images due to heat reflections of surface ripples. Continuing studies will provide the data necessary for the development of an accurate and costeffective passive detection and tracking system for marine mammals