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From: Brendon
Category: Shipwreck Research
Date: 04 Jun 2004
Time: 04:26:49
Remote Name: 24.196.69.62
Craig,
There have been some advances in ASF algorythms, which attempt to compensate for the theoretical land mass propagation factors at any given point, given the LORAN chain and transmitters being used. However, this is not a straight calculation and relies on a large, complex database of correction factors that require you to know the transmitters used to plot the original TDs. The Coast Guard's conversion software uses a straight theoretical conversion and is quite crude by comparison. All the conversion software using ASF correction is commercial and is expensive. There has been quite a lot of research surrounding this issue in the past 10 years and much of it is online. If you have a few hours to kill, you might do a search for LORAN and ASF Correction. I last researched this topic last year, and at that time, it still appeared that even the best ASF correction software still wouldn't do a good job of turning LORAN numbers into good Lat/Lon. As has been suggested, the only reliable way to get good Lat/Lons is to relocate the site with a LORAN receiver, then take a GPS measurement. The conversion software will almost always put you in side scan range, but alas, few of us hobbyists have such toys.
BB