Sonar

I am definitely not an expert in sonar, but I did a quick search and found several examples of sonar working at 300m and 1000m, and even up to 6000m. Here are a couple of them:

• Cavity Profiling Sonar Systems
• Imaging sonar

Hope this helps.

thank you for replying. But most of the info was based on underwater systems. but actuall i'd like to know if sonar works for long range in air?

Sorry, I didn't get that part of your question - a very different question indeed.

Perhaps you are asking about SODAR

http://www.sodar.com/about_sodar.htm (link no longer available)

"Sodar (sonic detection and ranging) systems are used to remotely measure the vertical turbulence structure and the wind profile of the lower layer of the atmosphere. Sodar systems are like radar (radio detection and ranging) systems except that sound waves rather than radio waves are used for detection. Other names used for sodar systems include sounder, echosounder and acoustic radar. A more familiar related term may be sonar, which stands for sound navigation ranging. Sonar systems detect the presence and location of objects submerged in water (e.g., submarines) by means of sonic waves reflected back to the source. Sodar systems are similar except the medium is air instead of water and reflection is due to the scattering of sound by atmospheric turbulence."

SODAR is used in ranges from a few 10's m to 4-5 Km (depending on the frequency)for vertical profiling of the low atmosphere (the boundary layer). Since raindrops, birds, nearby tall buildings, and airplanes are causes of false echoes, I assume that SODAR mods could also be used in those kinds of detection applications, with proper design. I do not know of any references for these kinds of applications.

Sonar is specific to underwater sound applications. I presume you are inquiring about acoustic location. There are two types: Passive techniques (object being detected emits sound) were used before the advent of radar to detect incoming aircraft. The technique had the advantage of long range detection and could be used for approximating a bearing to the object. Your concern appears to be active techniques. There are few uses of active acoustic location techniques in use. This is due to the many issues which limit the useful range of sytems using sound. Therefore, the simple answer to your question is No. To build a reasonably accurate systems, you would utilize the higher acoustic frequencies (ie: ultrasound) but the signal loss limits the useful range. For your application you would require a large, broadband focused emitter and sophisticated signal and sensor processing to mitigate the effects of signal loss, reflection and multi-path fading, pressure, humidity, temperature, wind effects, gas composition (especially carbon dioxide) etc..etc..etc.. In contrast low frequency techniques would allow for a huge range but accuracy is compromised due to ambiguity and fading. Hope this helps.

Bingo.

Fairly recently it was discovered that elephants use infrasound to communicate and coordinate among themselves at distances up to 4 km. Ordinary frequencies perceptible to we humans do not travel such distances without considerable attenuation. Higher frequencies are attenuated faster, which explains why only the deepest rumblings of distant thunder are heard but not the crash and crackle from nearby lightning. Acoustically speaking, air becomes more and more lossy as the sound frequency increases. Eventually the energy of the sound wave is dissipated as heat. The higher the frequency, the faster the decay.

So, at its simplest level, the problem basically boils down to one of trading range for resolution. Engineering is truly the Art of Compromise, yes?

-e

The answer is definately YES, if you need to have some information on sonars let me know , contact me on Don@hydro-products.co.uk

Pleased to help

Cheers

Don

sound propagates well in water as water is not compressible. In air you get a lot more attenuation and the return signal is similarly attenuated.

That said, for short rages it works quite well, as bats use it happily.

I am not sure if you could get 1000s of meters of range in air with any resolution

From your answer I gather you are enquiring about acoustic detection/location of a reflector in air. As well as many other factors, i.e., power transmitted, sensitivity of echo detectors etc, it depends a lot on the size, nature etc of the target/reflector. I regret that your question is too simplified to give an informed answer but simply put, the answer is yes. Basically you need to understand that in order for sound energy to be returned (echoed) there has to be a physical discontinuity in the transmission path. It would help if you understood a little about electrical transmission line theory because this is most highly developed and lends readily to mathematical analysis. You will see that echoes depend on a change in the characteristic impedance of air to that of the target. The transmission line analogy is simpler because the target (line termination) does not have a shape as might a building or an aircraft for example and all the reflected energy goes back up the line. There is no spatial scattering although there might be frequency shift.

What are you trying to detect? I am not sure about Sonar in particular, but Lidar and Radar are very good at long ranges - we have the doppler systems that give us coverage of the entire state with a few transmitters. I have seen some Lidar security systems that work out to the ranges you mention.