Locating OH2

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Locating OH2

I put in two SSM (Standard Surveying Monument - a rebar stake set in cement) at OH2 and surveyed the important points from one of them in relation to the other. But how to get these 2 SSM, and consequently the rest of OH2, into our grid? The distance from a known monument high on a hill was too far to use stadia techniques. And taping the more than 500 meters up and down slopes was impractical. Our EDM is in disrepair. Fortunately Abed Salamin, a Syrian surveyor from Hasake, generously come to Mozan with an EDM and quickly gave us the horizontal distances we needed. (He measured from SSM number 313 to OH2 points 1867 and 1868, and also from GS1 to 1908, the western edge of the well excavation, OP2.) With this distance data we could move ahead.

I set up the theodolite on 313 and took a O° backsight to GS1. Jim Walker stood with the rod on each of the two monuments in OH2. At each monument he held an orange tape case for visibility, centered at 1.5 meters on the rod, which is approximately the theodolite instrument height. From this I took zenith angles which give elevations. And, at each monument, I read horizontal angles to the center of the rod, and doubled the angles for accuracy. I was surprised how visible was the rod at 500 meters, and felt confident in the readings.

With these angles and the EDM distances I could calculate the coordinates and elevation of each of the monuments in OH2, and from these locate each important point there.