The Challenge

The U.S. Army Corps of Engineers (USACE) is responsible for maintaining approximately 25,000 km of navigation channels and more than 600 ports and harbors. These channels must be assessed, often annually, for the movement of sand and sediment into shoals that impede safe navigation. Many channels require repeated dredging. Conventional hydrographic surveys using boats with acoustic fathometers are costly, slow, and do not meet all the USACE requirements for navigation and shore protection project monitoring.

Remote Sensing Application

USACE developed an airborne lidar system that allowed it to survey more channels without increasing its budget. The lidar technology works by transmitting green and infrared laser signals into the water. The green signal reflects off the sea bottom, and the infrared signal reflects off the water’s surface; the time differential between the two signals provides the water depth. The USACE’S objective was to stimulate private industry interest and investment in the technology by demonstrating the viability of lidar through the development of the Scanning Hydrographic Operations Airborne Lidar Survey (SHOALS). SHOALS was initiated in 1994. After demonstrating the technology and characterizing its capabilities, the USACE adopted the technology and SHOALS for operational use. SHOALS remains a government-owned, privately operated system.

Results

The lidar system can survey waters too shallow to allow boats to collect data and can extend the hydrographic survey onto the beach or shore. The information obtained by SHOALS at a navigation project, including ebb and flood shoals, adja