Hydrographic surveys are the best and most accurate means of obtaining detailed and specific information concerning the BLS. However, these are normally prepared only for large-scale amphibious landings by U.S. Navy sea-air-land (SEAL) units or United States Marine Corps (USMC) reconnaissance (recon) units. It is not always possible to obtain as much detailed information on a BLS because of time limitations and the covert nature of the mission. Army terrain teams may also be able to supply applicable hydrographic information. Their duties include supplying information on coasts and beaches as well as inland waterway analysis. In these instances, up-to-date nautical charts, tide and current data, and photo reconnaissance provide the minimum data needed.