<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style=""><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;"><br></div><span style="font-size: 13px;">MIT has published a paper on underwater positioning using Underwater Backscatter Localization which</span><div><span style="font-size: 13px;">might be of interest to some folks on the list.</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;">Although it seems more focused on positioning of un-powered or under-powered objects (fish, drones, etc</span><div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;">- surface vessel knowing the position of an underwater object), and it's only a proof-of-concept</div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;"> (the paper on covers 1D positioning, we'd really need 3D), it does offer some hope for a relatively cheap</div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;">underwater positioning system in the future.</div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;"><br></div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;">The paper can be found here:</div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;">http://www.mit.edu/~fadel/papers/UBL-paper.pdf</div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;"><br></div><div style="color: rgb(0, 0, 0); font-family: arial, sans-serif; font-size: 13px;">There is a kind of layman's summary here:</div><div style=""><span style="font-size: 13px;">https://hackaday.com/2020/11/08/under-the-sea-gps-uses-sound/</span></div></div></div><div style=""><span style="font-size: 13px;"><br></span></div><div style=""><span style="font-size: 13px;">Pity there isn't a a cheap sonar "hackers" kits (although some have do things with PC sound cards).</span></div><div style=""><span style="font-size: 13px;">On the radio side of things I can take a USB SDR (Software Defined Radio) and build a radio telescope</span></div><div style=""><span style="font-size: 13px;">for well under $100 (actually, I think it was under $50 in the end), would be great to be able to have</span></div><div style=""><span style="font-size: 13px;">that flexibility for playing with sonar.</span></div><div style=""><span style="font-size: 13px;"><br></span></div><div style=""><span style="font-size: 13px;">Cheers,</span></div><div style=""><span style="font-size: 13px;"> Ian.</span></div><div style=""><span style="font-size: 13px;"><br></span></div></div></body></html>