USGS CMG D-L1-97-CA Geodetics

 DL197CA  Notes:
 This was Ms Horsman's first attempt at running a total station survey. Her field notes indicate some 
 discrepancies with the heights of the total station and stadias used.
 1) Field-notes would suggest that 51.0cm must be subtracted from all observed Instrument 
 Height readings. This would result in instrument heights that would be unreasonably low (<1m). 
 THE ASSUMPTION THAT THE ORIGINAL UNCORRECTED INSTRUMENT HEIGHTS ARE INDEED CORRECT IS BEING MADE. 
 Since differences between the actual and recorded heights of the total station will only result in a 
 bad beach elevation at the total station, the validity of this assumption can be checked by looking at the 
 total station spot elevation when the instrument was set up "on-line". The elevations along the profile 
 should show a reasonable trend. The reason for the noted correction is uncertain. 
 2)Hand-written notes from the field would suggest that two different stadias were used in the 
 field. This reference only appears once, at New Brighton State Beach where Ms Horsman refers to 
 "1st 33 pts with single prism". This may refer to the stadia with a single prism holder 
 (typically used for water-work). She goes on to write: "next pts done with hydro prism" which I 
 take to be the stadia with the multi-prism holder (as referenced in the notes from Seacliff State Beach 
 where she writes: "used hydro prism but not sure of orientation of prism on rod (height may differ)". 
 Only the multi prism holder can be mounted on the stadia in an inverted orientation. For post-processing purposes, 
 THE ASSUMPTION THAT ONLY THE MULTI-PRISM HOLDER ON REF1 STADIA ROD WAS USED FOR ALL SURVEYS IS BEING MADE. 
 This may result in vertical errors amounting to 0.064m if there was in fact a second stadia used.
 3) Ms. Horsman used a value of 0.771m as the shortest stadia length, recorded both in field 
 notes and the instrument's internal memory. The actual length is 1.769m for the REF1 stadia with an 
 inverted multi-prism holder. THE ASSUMPTION THAT THE "1" WAS INADVERTENTLY REPLACED BY A "0" IS BEING MADE. 
 4) Ms. Horsman makes reference to reducing some stadia lengths by 0.150m. (25.8cm-10.8cm, "length of 1st 
 prism - length of hydro prism" - New Brighton State Beach notes). No reasonable explanation can be found for doing so. 
 THE ASSUMPTION THAT ADDITIONAL CHANGES TO THE STADIA HEIGHTS IS UNNECESSARY IS BEING MADE.
 5) Only one of the control points surveyed in the field corresponds to the control points 
 surveyed using GPS. Accordingly, the UTM conversion had to take place at a later time when both GPS control 
 points were surveyed simultaneously.