The Chapter asked me to give a 90 minute mini-seminar on Astro observations (solars mainly). I said OK but I'm not an expert.
I just got interested in seeing if I could figure it out for fun and also it will be useful in some of the work I do where GPS is not very practical. So the word got out and they asked me to teach it.
I set up a baseline in my front yard. I set a 12" spike it a fairly GPSable spot (it is just west of my 8" red oak tree but has southern sky) which sees a yellow steel gate post 740' east of me. Unfortunately the gate post is under overhanging canopy from a tree; I might be able to get a good static observation on it but I would prefer something cleaner.
First I observed Polaris using my Total Station and got an astronomic bearing. Then a week later I observed the Sun (hour angle) using my Dietzgen 1' Transit and got a bearing about 6" from the Polaris bearing which I consider to be pretty good. Then I did a solar with a Wild T1 I found under a desk at work, it is out of adjustment but doing D&R cancels the problems. I got a bearing 1" from the Polaris bearing.
Now I want to get a GPS vector on my baseline; I think I will set a magnail on line between the 12" spike and the gate post and use that for the vector. I could just set a random point and turn angles to the gate post as an alternative. The plan is to convert my astronomic bearings to geodetic bearings for comparison.
I am using my alarm clock which automatically sets itself to NIST UTC (I checked it by calling the phone number and it is accurate). The only thing I haven't done is do the DUT correction but that is simple enough. My new Excel workbook solar calculator has a spot to add the DUT correction so I use UT1 for the calculation.
All of this has been done by projecting onto a card which is simple to do. I think I need to get a solar filter for my Topcon TS :-).
Not sure you have a long enough line for the GPS vector. Check what expected centering and GPS accuracy compute out to be in azimuth uncertainty.
Yes, it is a bit short but that's the best I can do from my front yard.
It's mostly a science project and a baseline to use for checking my compasses so even a minute of error isn't a big problem.
sounds like good work.
The 6" variation seems to be right.
Of course, this all depends on the redundancy of your work like any aspect of survey measurements. You always need to toss some data. Time is critical so the DUT needs to be applied.
Pre-gps, I did solars with anything from a 1” theodolite, 3” TS and 30” transit. Some with a filter and some with projections on card stock or field book covers. All were acceptable.Polaris shots are always iffy here because of our Lat and the amount of humidity in the air for most of the year. It is only in the winter months when one can get nice clean sky for celestial observations.
I don’t know why people do not like an eccentric station for GPS work if it offers the best solution but some do.
Dave,
I am willing to let you BORROW my Roelfs Prism for a couple of weeks to experience that. It will probably fit on the T1. What is the size of the sun shade in mm? What are you willing to put up for collateral?
Luke
