CHIRPing bottom all the way to Bermuda, maybe fish too!

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

10 Responses

  1. Bill Bishop says:

    Ben, I’m betting it isn’t a fish, although I would like to think so. Given the cone width at that depth, and the apparent scale of the structure/fish it would have to be huge. That being said, the Kraken has to live somewhere.

  2. Ben Ellison Ben Ellison says:

    Interesting comment about that last screen shot from a friend:
    “I don’t know— I’d venture at that scale you’d see bottom features but it would be tough to see fish—if fish were even to school at 11,000 feet.
    It pretty dark down there, and only the occasional blind copepod or annelid to dine upon.
    I’d say what we are seeing is a piece of bottom geography.
    This {bit from the Garmin blog} indicated to me that detail may be lacking, though its a good example of reading the bottom , useful perhaps more for bathy data than creatures.
    “”Keep in mind that at these depths, the ping rate is very slow – limited to the speed of sound in water – this screen image represents over 2 hours of time and about 24 miles of bottom.””
    This is a huge area in which to attempt to see a fish. Even a 10 foot fish—let see:
    24 miles= 126,720 feet
    15-inch screen is 1,024 pixels wide.
    126,720 feet of travel / 1024 pixels = 124 horizontal feet represented by each pixel.
    Seems you’d have to have a fish at least 124 feet long to register as a pixel
    Does this make sense?”

  3. Rick R says:

    Maybe its a sunken ship

  4. AaronH says:

    That’s pretty amazing to keep a bottom lock that deep!!! I’m curious if they took some screen shots of the mystery echo in the last imaged with the plotter “zoomed in” on the bottom range, because your math makes sense. Here’s some other math that I’ve been pondering:
    The R599 Low-Chrip’s beam is 9 degrees, so by my trigonometry:
    2 * 16787 * (tan 4.5) =
    2 * 16787 * 0.0787017068 =
    2 * 1,321.16555 =
    2,642.3311 ft
    At the seabed, the beam is now about 2,642 ft wide!! So even a small fish may return quite large on the screen anyway.
    I’d be curious to see what the sonar’s inherent resolution is at that range, independent of the display’s resolution.

  5. Ben Ellison Ben Ellison says:

    Thanks, Aaron. This is becoming a good lesson in how sonar “sees”. I’ve always liked how the “A” Scope on Raymarine sounders shows the cone diameter of the bottom seen (if it knows the specifics of the transducer). In other words, it (and maybe other fishfinders?) does the trig you just did.
    You can sort of see what I’m talking about in this five year old Panbo entry:
    Which also speaks to how far the technology and particularly Garmin’s has come.

  6. Larry Brandt says:

    But WHY does one need a sonar with that kind of capability? And at WHAT COST to the environment?
    What frequency does this thing operate at? Have any studies been done, or marine biology experts been consulted, to ensure that the marine life down there aren’t under threat from all that sonar banging?
    How would you like to have some kid banging on a trash can lid whenever they pass by, day or night?
    This device must be a very high power transducer, which means LOUD. And if it operates in or near the audio range that sensitive marine life depend on for their existence it shouldn’t be produced. In fact, I wish my relatively puny Raymarine depth sounder had a ‘transducer disable’ offering on its menu so that I could disable my transmissions (without disabling my other instrumentation) when I am in the vicinity of whales here in the Pacific Northwest.

  7. Brian Vlad says:

    Raymarine echosounders have a ping enable/disable which turns the transmitter off.

  8. Bill Bishop says:

    Larry, it is an important question, but in this case the frequencies used don’t bother fish or whales. Whales communicate at around 300 HZ. The current Chirp fish finders operate from 28kHZ to about 210 kHz. The power output is 3000 watts max. Much lower frequency, high powered sonars used for military applications are generally believed to bother some sea life, and especially whales. The Garmin GSD 26 can also disable the ping/chirp, and both system moderate power based on depth.

  9. Ben Ellison Ben Ellison says:

    I sure don’t think we should be abusing sea life, but like Bill I’m not sure that CHIRP sonar will do that. It performance enhancement is mainly derived from more information (frequencies) being put in the water, and lots of signal processing of what comes back, not more power. It just happens that Garmin also puts lots of power in its CHIRP fishfinder and I think it’s the combination that results in such amazing depth performance.
    But sonar power is relative, and I doubt that any recreational sonar is exceeding what the commercial, scientific, and military worlds are up to. Years ago when I visited Simrad’s Horten, Norway, sonar facility (now part of Kongsberg Maritime’s Simrad Fisheries division), I saw side scanning transducers more than three feet in diameter that they wouldn’t let me photograph.

  10. Reed Erskine says:

    On a cruising sailboat in offshore waters, the depth sounder is just another battery drain. I put a relay on the power supply to my Raymarine depth sounder module and ran a line back to a switch on the helm to depower the sounder. A “lost data” alarm sounds when I turn off the sounder, but the alarm quits squawking after a minute. Unless the device is being used as a fishfinder, a sailboat only needs continuous depth info in specific cruising areas like the Bahamas or the Coast of Maine.

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