Pushing Boundaries

Egads! LADS!

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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.

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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)

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Red Laser is fixed vertically/stationary to measure height.
Green Laser scans a 240m swathe maping the ocean floor.

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

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Read more at hydro.gov.au!

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Images and research via 5dme.net, navy.gov.au, Wikipedia, airliners.net, and hydro.gov.au.

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  • nanoop

    Nd:YAGs are around 1064nm, ca. 3x10e14Hz, and the 990Hz are a modulation, FSL or something? The rest makes sense.
    EDIT: it's "990 soundings per second".

  • cruisintime

    Did you Lube Your Cube ?

  • Felis_Concolor

    You misspelled Patagonian Toothfish.

  • texlenin

    Civilin pilot? that some kinda new gangsta thing?
    Also, how well does this rig find fish?

    • http://hooniverse.com/ HycoSpeed

      Well, crap. Either I can't type or I can't spell! Now, do I fix it, or just leave it to become a staple of slang?

  • nanoop

    Me too, even the same company. They were cheap mid-power in the nineties, I guess. There was a phase in my life when I shared more time with that thing than with Mrs. nanoop, which wasn't her fault.

    I still wonder if 1064nm is just a coincidence or a design target, because it's perfect: just visible with Si detectors, the doubled frequency is perfectly visible for human eyes and not red (HeNe already available then), and usable for pumping Ti:Sa, which can be tripled to be blue, or Rhodamine to lase in orange etc… aah, the good old times, I get the Atomic Toasters feeling…

    Sorry HycoSpeed if I sounded like I meant to correct the internet, me in paper correction mode must be an ugly sight.

    • http://www.washington.edu/news/archive/52703 mdharrell

      Mine was an early Model 416, making it a bit long in the tooth when I started in the mid-'90s. It's still in use.

  • OA5599

    Wouldn't it have been easier to simply obtain a Ph.D. through one of the several providers that advertise in in-flight magazines instead of having to acquire an instrument that generates one?

    • http://www.washington.edu/news/archive/52703 mdharrell

      Right, as if I had money for commercial flights while in grad school.

      To answer your question, however, yes.

      • OA5599

        With diploma processing specialists, life experience can substitute for grad school. Instead of paying years of tuition, you could have stocked up on tiny bottles of booze, and still ended up with a piece of paper displaying your name and some consonants.

    • nanoop

      Well, as a former minister of defense..
      <img src="http://assets.diylol.com/hfs/fd1/566/e2d/resized/guttenberg-meme-generator-ctrl-c-ctrl-v-ebbd28.jpg&quot; width="200">
      He couldn't defend that.

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