Alaska Peninsula deployment of laser airborne bathymetric system

Abstract

Laser Airborne Depth Sounder (LADS) systems provide an accurate, rapid, safe and cost effective method of surveying coastal areas. The system has been used by governments and commercial organisations over the last decade to conduct surveys for nautical charting, coastal zone management, territorial sea baseline determination, offshore exploration and defense applications. In the field of nautical charting, commercial LADS surveys have been performed in Europe, the Middle East, Australasia and Scandinavia. This paper describes the conduct of LADS Mk II survey's for NOAA in Alaska during April - July 2003. The LADS Mk II system consists of an Airborne System for data collection and a Ground System for data processing. The Airborne System is fitted inside a Dash 8-200 series aircraft, which has a transit speed of 250 knots at altitudes of up to 25,000 feet (7,620 metres) and an endurance of up to eight hours. The aircraft is certified by the Civil Aviation Safety Authority Australia, to Regular Passenger Transport standards and is fitted with the Traffic Alert and Collision Avoidance System. Survey operations are conducted from heights between 1,200 feet (366 metres) and 1,800 feet (549 metres) at ground speeds between 140 and 175 knots. The aircraft is fitted with a Nd: YAG laser on a stabilised platform. The laser operates at 900 Hertz to provide 5/spl times/5 metre laser spot spacing in the main line sounding mode of operation across a swath width of 240 metres. The electromechanical scanner also provides higher density modes of operation with laser spot spacings of 4/spl times/4, 3/spl times/3 and 2/spl times/2 metres with reduced swath widths. Green laser pulses are scanned beneath the aircraft in a rectilinear pattern. The pulses are reflected from the land, sea surface, within the water column and from the seabed. The green returned laser energy from the land or sea surface and the sea floor is captured by the green receiver and then digitised and logged to Digital Linear Tape. An infrared laser is directed vertically beneath the aircraft. The height of the aircraft is determined by the received infrared laser pulses and this is supplemented by an AHRS inertial height reference and GPS height. The LADS Mk II system can operate by day and night. Real-time positioning is provided by Wide-Area Differential GPS (WADGPS) and civilian GPS. During the survey in Alaska no WADGPS service was available. The Airborne System also contains GPS signal logging for use in determining post-processed DGPS and KGPS positions.