Oh and system currently has GPS speed correction very high accuracy has a stainless steel body with user serviceable boards, adjustable transducer angle and a set of filters for improving data quality. I originally modified any fish I could get second hand but have now produced my own. the software and firmware took 6 months to make but is not expensive to build.

Making from scratch the transducers are the hardest bit to make or most costly bit to build. Any one want any info on building buying or fixing them let me know.
Robin

With reference to your email see below:

Hi, You cant classify something as how highres is it but Ill try.
It depends upon the transducer beam width, frequency ping repetition rate, signal to noise ratio and the boat speed mainly although the ADC capture hardware should be good enough to not limit the resolution available by the transducers. The transducer frequency effects resolution. The lower the frequency the wider the scan but the lower the resolution in a straightforward traditional system.

Think of the transducers as a camera lens and the cheaper they are the worse the picture.

The main factor in new sidescan is the dynamic range as this allows you to pick out the detail and surface undulations. The monitor unfortunately will only display so much dynamic range and your eyes will only pick out so much so the latest sonars including the one we are just finishing are variable dynamic range so if you cant see all of something because its too dark you can shift it to bring out the detail in the lower or higher areas. Its not a contrast or brightness control its allowing you to digitise more data than you can see and then choosing which bit you want to see. in 256 shades of grey you cant notice a change in 6 shades if next to each other but if you shift the difference between each shade to be larger you can see the changes more accurately.


Any way we havent finished testing this yet but the system will be the same it will be a fish about 2ft long with two transducers to suit the application.

Standard fish is 200kHz which resolves objects about 1-2ft across on short range and much bigger at long range. You can resolve on close range to 2" if you up the sample rate BUT the picture will not be as good as the beamwidth allows only longitudinal resolution equivalent to a the beamwidth at the distance you want to scan AND so long as your boat travels at a velocity slow enough get all these widths one after another or you will get a disjointed picture with gaps and miss out key detail. As a result of the elevation resolution being whatever you resolve it to and the longitudinal resolution being limited by the speed and beamwidth you get stretched details if you oversample one instead of square pixels. This can be resolved by scanning at 90 degrees to the source and summing the two pictures but its very hard.

Plus as sound spreads out in water the further away you look(increase your slant range)the wider the beamwidth so the less your resolution. This also means you have to sample less often for longer to pick up the acoustic reflections form further away. hence even if you sample at a high sample rate you are over sampling and seeing nothing new. this is where multibeam and synthetic aperture sonar are now investigating.

There are also lots of issues such as multipath reflections giving ghost images at different ranges and saturation of the transducer at close ranges on sharp rock and metal surfaces (like trying to see an object in the snow with the sun behind it)!

You have fish with FMCW chirp generators said to give more resolution but In radar it is mainly used for controlling the power to get the best image at all distances (shallow water running)and for also transmitting with less power requirements. I have never heard of big resolution gains from this.

sonar also has no way of telling what angle things came back from hence the inability to resolve multipath echoes from the same source at but rebounding and producing different delays to the same signal.
Multibeam uses two or more transducers to resolve the angle of return and effectively direction find each signals true return. It is somewhat lacking in resolution currently and is stupidly expensive.


What do you intend on doing with it you need to buy the right kit for the right job.

If you want to search for big objects 100kHz to 200 is fine. Smaller things you want 200 to 600kHz.

I can do both but we need to get transducers to put it together and I currently buy mine which are quite expensive. The idea I had with my system was to allow people with legacy fish to upgrade to digital surface unit and eventually a digital fish.

If your willing to find an old fish or buy new transducers the rest is easy.

Robin

I would be very interested to learn about the system and would be interested in assembling a kit of parts to make the SSS. Alternatively, I would like details of the non technical parts and just buy the transducers and the electronics bottle etc. Can u help me please. Rgds ColinT

DiverBob , here in the US. I am interested in building a soild unit for underwater body recovery as the ones we have here are $$$ very expensive. HOw can you help me out to build one. I can cannot build programs, but could buy the parts and put one together. I would need a tow fish, software and all the components. Thanks alot for your help.