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Good day in the field

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I haven't been getting out much lately, so took Friday to go hunting in superb weather, and had a good day.

-Found Good, one that was last reported in 2006. I ran a 6-hour GPS static session and expect to submit a Shared Solution to the GPS On Benchmarks program.


-Found Good, one that was last reported as probably destroyed


-Found Good, trivially easy one last reported in 2006


-Found a stem where I expected a RESET as MH0029, but hadn't read the data sheet for the original and now am confused. I have to go back to see if this was perhaps the original.


-Tried to find one on an abandoned bridge, but was defeated by 18 inches of dirt, ballast rock, and roots on the old bridge deck. It is likely there under all that.


Last reported as NF probably destroyed (obviously I didn't need the metal detector)



GPS set up:


Edited by Bill93
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do you have to measure down to it from the flat plate and include that in your submission

Yes. You must provide the height in meters above the mark to the antenna reference point (ARP) when submitting to OPUS. I calculate that by measuring to the rim of the ground plane and solving the right triangle to find its height then subtracting its height above the ARP.


Actually I made a table with a spreadsheet and pasted it in the back of the field book.


Some manufacturers have all that built into their own processing software so you just give their program the slant distance, but OPUS doesn't do that.


OPUS does look up the antenna type you enter and takes care of the antenna phase center relative to the ARP. That value is different for L1 and L2 signals and even for different elevation angles from the satellite, but they have calibration tables for dozens (hundreds?) of different antenna models so you don't have to worry about that.


I ran sessions on 4 marks to compare with other peoples' GPS height values before I convinced myself I had it right. The first three all came up a cm or two higher than the other peoples' values and I was worried I had it wrong, but finally decided that was just the roll of the dice. Typical vertical repeatability for 2 or 4-hour sessions is in the very few cm range. Horizontal is tighter.

Edited by Bill93
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I live in Cedar Rapids. Was it a family or business visit? If you get out this way again, send me a message.

Business. Railroad industry meeting on the Iowa Northern railway, between Cedar Rapids and.. Waterloo, I believe. :)

Will do! Since we had time at one of our locations (Vinton, IA) I was able to quickly grab the one on the depot there.

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