LIght Detection And Ranging, or lidar, is a method used by NOAA's contractors to measure elevation or depth by analyzing pulses of laser light reflected off an object. These survey systems are typically aircraft-mounted and provide seamless coverage between land and sea. Bathymetric lidar refers to its use to determine water depth.
Bathymetric lidar systems use laser pulses received at two frequencies. Water depths are determined by measuring the time delay between the transmission of a pulse and its return signal detecting the seafloor. A lower frequency infrared pulse is reflected off the sea surface, while a higher frequency green laser penetrates through the water column and reflects off the bottom.
Analyses of these two distinct pulses are used to establish water depths and shoreline elevations. Depending on water clarity, these systems can reach depths of 50 meters.