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Discussion » Statements » Rosie's Corner » Can bat radar identify something as fine as spider web? What about military radar? What can it pick up and what can it NOT pickup?

Can bat radar identify something as fine as spider web? What about military radar? What can it pick up and what can it NOT pickup?

Posted - June 23, 2019

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  • 46117
    This might help   It does not address exactly what a bat can pick up, but it shows how it is done.  

    HELLLOOO! LOOH. Looh. looh.

    If you have ever heard an echo, you’ll be familiar with the basic principle behind three similar technologies: radar, sonar and lidar.

    An echo is the reflection of sound waves off of some distant object. If you shout in a canyon, the sound waves travel through the air, bounce off the rocky walls and then come back to you.

    Sonar (SO-nahr) is the most similar to this scenario. This technology also relies on sound waves to detect objects. However, sonar is typically used underwater.

    This sonar image shows the entrance to Portsmouth Harbor, N.H. Lower areas are in blue, higher areas in red.

    NOAA/NOS/Office of Coast Survey

    Medical technicians also may use sound waves to peer inside the human body (which is mostly water). Here, the technology is known as ultrasound. When bats, dolphins and other animals use sonar naturally, usually to find prey, it’s called echolocation (EK-oh-lo-CAY-shun). These animals send out a series of short sound pulses. Then they listen for the echoes to determine what’s in their environment.

    Radar and lidar (LY-dahr) rely on echoes, too. Only they don’t use sound waves. Instead, these two technologies use radio waves or light waves, respectively. Both are examples of electromagnetic radiation.

    Scientists made up the words radar, sonar and lidar. Each reflects a technology’s usefulness:

    ·         Radar: ra(dio) d(etection) a(nd) r(anging)

    ·         Sonar: so(und) na(vigation) (and) r(anging)

    ·         Lidar: li(ght) d(etection) a(nd) r(anging)

    Detection (or navigation) refers to locating objects. Depending on the technology, these objects may be underwater, in the air, on or below the ground, or even in space. Radar, sonar and lidar  can determine an object’s distance, or range. For that measurement, time plays an important role.

    This radar image shows a December 19, 2009, snowstorm (blue, green and yellow) as it approaches the U.S. Mid-Atlantic region.

    NOAA/National Weather Service

    Lidar, radar and sonar systems all include timing devices. Their clocks record the length of time needed for a wave to travel to an object and back. The farther the distance, the longer it takes for an echo to return.

    Radar, sonar and lidar also can reveal information about an object’s shape, size, material and direction. Air traffic controllers use radar to spot aircraft in the sky. Police use it to detect speeders. Navies use sonar to map the ocean bottom — or to look for enemy submarines. And lidar helps read the lay of the land or features on Earth’s surface. Lidar’s laser pulses can penetrate forest cover to record the shape of the ground below. That makes this technology especially valuable for mapping.

     

    Power Words

    (for more about Power Words, click here)

    echo    To bounce back. For example, sound bouncing off walls of a tunnel, and returning to their source. Radio waves emitted above the surface can also bounce off the bedrock underneath an ice sheet — then return to the surface.

    echolocation   (in animals) A behavior in which animals emit calls and then listen to the echoes that bounce back off of solid things in the environment. This behavior can be used to navigate and to find food or mates. It is the biological analog of the sonar used by submarines.

    laser   A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.

    lidar   (short for light detection and ranging) A tool to measure the shape and contour of the ground from the air. It bounces a laser pulse off a target and then measures the time (and distance) each pulse traveled. Those measurements reveal the relative heights of features on the ground struck by the laser pulses.

    navigate   To find one’s way through a landscape using visual cues, sensory information (like scents), magnetic information (like an internal compass) or other techniques.

    radar   (short for radio detection and ranging) A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land — even land covered by ice.

    radio waves    Waves in a part of the electromagnetic spectrum; they are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals; it is also used in radar.

    range   The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (In math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

    sonar  (short for sound navigation and ranging) A system for the detection of objects and for measuring the depth of water. It works by emitting sound pulses and measuring how long it takes the echoes to return.

    sound wave    A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

    ultrasound    (adj. ultrasonic) Sounds at frequencies above the range that can be detected by the human ear. 

    This post was edited by WM BARR . =ABSOLUTE TRASH at June 24, 2019 2:44 AM MDT
      June 23, 2019 10:42 AM MDT
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  • 113301
    Thank you for your thoughtful informative and extremely comprehensive reply to my question Sharon. I appreciate. It all started with wonder why flies get caught in spider webs if they can "see" them. From small pebbles we build pyramids? :)
      June 24, 2019 2:45 AM MDT
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  • 44175
    Bats use echolocation, or what some refer to as sonar. With sonar, anything that can be vibrated by the waves can be detected, So a bat should be able to detect a spiderweb. I doubt if there is any research about it. Radar waves can reflect from  anything larger than it's wavelength, although the detection receivers are not sensitive enough to give a visualization of very small objects. We can detect rain, but not individual raindrops.
      June 23, 2019 3:54 PM MDT
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  • 113301
    I wondered how flies get caught in spider webs if they can SEE them. Why they don't avoid them? Then I wondered about bats and other forms of "seeing" without really looking. So radar can detect rain (the forest) but does not distinguish the individual raindrops (individual trees). I wonder if humans do that too? See the grand scheme of things but are unable to comprehend the details? I'm gonna ask. Thank you for your helpful explanation. That's a very nifty word. Echolocation. Echo location.  :)
      June 24, 2019 2:49 AM MDT
    1

  • 3680
    I found some basic figures. The wavelength of a bat call at, say, 120kHz, is about 0.3mm. And it's not "radar" but equivalent to sonar.

    Spider silk seems typically to be around 0.004 mm diameter, so in very round figures approaching one-hundredth of the call's wavelength,

    To detect anything, the wavelength has to be significantly larger than the target's width, so on those figures a bat will not locate a single spider silk, though it might obtain echoes from a dense web.

    You can see this effect with wind-blown ripples on a pond, with a wavelength of a couple of inches or so. They pass thin plant stems without change, but if they hit something wide like a rock or tree-trunk sticking out of the water, are reflected or refracted by it.

    Wavelength decreases as frequency increases, but so does range, so even if the bat could call at sufficiently high pitch to detect a spider thread, the call would have an extremely short range.
    '

    Military radar performance is not very likely something you'll find easily, though it does not have to detect anything very small. Most ordinary  marine radar seems able to pick up reflectors about a foot or so across, the size of the radar reflector you sometimes see on yacht masts.

    One application of radar though, that can find small items by using millimetric wavelengths, is the airport security scanner the dozy Press keeps calling an "X-Ray Machine". The power is very low and the exposure time very short, so it's safe; but it will as intended, find metallic objects hidden under clothes.

    I don't know how meteorological radar works, but I wonder if the mass of rain returns a sort of diffuse, overall reflection that strengthens with the intensity of the rain. 
      June 25, 2019 11:21 AM MDT
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