There are two distinct issues here. Tracking the search pattern, and identifying a target location.
A little about GPS.
If you are stationary:
The GPS signal, from each sat, is 3 seconds long. It takes a full 3 seconds to broadcast all of the data string. You need data from at least 3 sats to have a position. If you have only 3, you have no error trapping, and to have an accurate fix on your location, you will need to be stationary for a long period of time. If you have 4 sats, the unit can then have a balance to determine errors, and will attempt to leave one out if it encounters errors. This of course, takes time. If you have 5 sats, the system now has the ability to calibrate quicker, and leave one out. For full error trapping and accuracy, you need 6 sats available.
The time associated with a stationary fix, with a good level of accuracy, is based on receivong signals from at least 6 sats, at 3 seconds each (they are not at the same time) performing error checking with multiple data packs from each sat.
That is the stationary fix!
Moving fix:
Review all of the above!
Now, while you are moving, the GPS is calculating where you WERE, NOT where you ARE. Where you WERE takes some tme to calculate. Now, where you ARE, relates to the Kalman filter in the unit. The Kalman filter, as you are moving, takes all of the above positioning, and averages a rate of change. This rate of change, with speed and direction, is what the GPS reports on where you are.
When you make changes in speed and direction, the averaging starts over. (ie you turn, well...damn)
PRE-Conclusion:
Dont bother with trying to add GPS to the detector itself. Waste of weight, money, and accuracy.
Best available Solution:
Get a tablet with a WAAS puck, and carry it with you!
Add Open CPN to the tablet (so you can work without a wifi connection).
Map your site in Google Earth and download to OpenCPN.
Map a course or search path in openCPN.
Now, as you search, have tracking enabled. This way, the program will keep you on the path you have laid out, and also track where you are (you set the parameters of the track, I use set every 30 seconds on land and water)
Once you have a line set, you can do offsets. On water, the offest would be the scan width of your array, on land, it would be you swath width.
All of this is then recorded. Map an area, see what you have done, and build/go back. At anythime, you can hit fix and set a waypoint with description.
When back at home, you can dump this to Google Earth, and keep a permanent record. I also take images, so the locations can have images associated with the waypoints on GE as well.
on land or by sea...it works great!
(hope this helps!)
