Lasers are useful for a great many things, certainly up to and including being placed on the heads of irritable sea bass. For no reason whatsoever, this weekend will be the weekend of the laser here at Atomic Toasters, and we are going to start out by taking a look at a laser system that has proven to be quite useful indeed for those friendly fellows from down under. In the 1970s, the Royal Australian Navy noticed a lack of progress made in the surveying Australia’s territorial waters. There was much of the sea area that was was unsurveyed or simply old data from the age of sail, prompting the RAN to seek a method of effectively surveying large areas from the air. The Defence Science and Technology Organisation developed the LADS system, which stands for Laser Airborne Depth Sounder. The system began feasibility trials in is 1977, and although it was not operational until 1993, it is still flying today.
The basis of the LADS system is a Nd:YAG laser, which emits an infra-red beam at 990 hertz. This initial beam is frequency doubled to produce a green laser, which is then split into two beams, one infra-red and one green, by an optical coupler. The infra-red beam is aimed directly below the aircraft, and the green beam is scanned across the target area with a mirror. Each beam also serves a separate function with the system, as the infra-red laser does not penetrate the water’s surface, and its reflected beam gives the height of the aircraft above the surface. The green laser can penetrate the water down to the ocean floor, and that return pulse reflection indicates the height of the aircraft from the ocean floor. The system then takes the difference between the two values and calculate the water’s depth. In order to reduce system weight, the data collected from the laser is not processed by an onboard computer, but by a ground support team that syncs the data with the GPS information from the aircraft. The aircrew takes the laser on multiple overlapping passes to ensure full coverage and accuracy. “The LADS system is capable of taking 990 soundings per second, with data points positioned 2 to 6 metres (6 ft 7 in to 19 ft 8 in) apart across a swath up to 288 metres (945 ft) wide.The system is capable of working with waters up to 70 metres (230 ft) deep.” (Wikipedia)
Initially fitted to a Fokker F27 aircraft, and in 2010, the system was installed in a De Havilland Dash 8 aircraft. Typical crews consist of 2 civilin pilots, 2 Navy Hydrographic Survey Officers and 5 Sailors (Hydrographic Specialization). The laser system itself was upgraded in 2008 with the following changes:
–240m laser swathe (at a 5 x 5m grid pattern)
–Variable grid pattern of 5x5m, 4×4, 3×3, 2x2m (depending on what is being investigated)
–990 soundings per second (compared to 168 per second on the old system)
–49800 soundings per square km
Variable sounding height of aircraft from 1200ft to 2000ft
–Sounding speed 175 kts
Read more at hydro.gov.au!