Laser Airborne Depth Sounder (LADS) bathymetry data (Australian Hydrographic Office)

Brief description

LADS is a swath sounding system that collects data in a grid 240 metre wide, with a sounding at approximately every 10 - 11 metres. During normal survey operations parallel LADS survey runs are flown at 200 metre intervals, resulting in a 40 metre overlap between runs. A LADS survey run will have 24 columns of sounding data, of which 22 are useable. The soundings in columns 1 and 24 are not used for hydrographic purposes. Data along a LADS run is divided up into "FRAMES". One frame equates to two seconds of LADS data, an area 240 metres wide and 150 metres long. Each row or swath of soundings within a frame is known as a "SCAN". There are 14 scans to a frame. Thus a frame can contain up to a theoretical maximum of 336 soundings (pulses of the laser) in 24 columns and 14 scans (14 x 24 = 336). However as soundings in columns 1 and 24 are not used, therefore the total number of soundings in a frame is 308. Consecutive frames of data do not overlap. The centre of each frame has a GPS position applied to it. All other soundings within that frame will have their position calculated from the central position of the frame. Each frame also has a frame correction; corresponding to the tidal reduction, which is applied to all soundings within that frame.LADS survey runs are typically planned to be around 45 nm in length, although this can be varied. A run of this length will typically contain 550 frames of useable data or 169400 possible soundings. On a typical LADS sortie with 4.5 hours on task it is possible to fly 10 of these runs, as well as conduct a navigation calibration and fly a benchmark run. This equates to approximately 1.69 million possible soundings or an area surveyed of 52 sq nm. The largest area ever surveyed in a single sortie was 88 Sqnm. The area surveyed per sortie increases marginallyif the run lengths are increased but decreases drastically as run lengths are decreased, due to the lost time in turning between lines. Raw LADS data collected in the air is stored in binary form on Magneto Optical Disks. On returning to the ground the data is copied onto a single DAT tape, and is then automatically processed using the Ground Analysis Sub System (GASS) into a recognisable form.The available data covers the following survey areas:HI185: Flinders PassageHI193: Bunker Reef to Fairway ChannelHI220: Cooks Passage to Trinity OpeningHI221: Cape Weymouth to Blackwood ChannelHI221_2: Fairway Channel (NW Extension)HI241: Hope Island to Lark Pass© Commonwealth of Australia (Australian Hydrographic Office).

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Data validation:An overview of the LADS digital data and processing and validation techniques is given in the document titled "Laser Airborne Depth Sounder (LADS) Digital Survey Data".