OPUS and the Local Weather Pattern
On a recent project, I left my dual-frequency receiver logging observations on a convenient control point, CP1 on the map below, for over four hours on two days in order to get static OPUS solutions for the NAD83 (CORS96) Epoch 2002.0 position of the point. I only got 5hrs 31min worth on Day 178 as afternoon rains ended the field day early but had 7hrs 05min from Day 179.
A single OPUS-Static solution from more than 5 hrs of observations at a wide open site such as where I had the L1/L2 Microcentered Antenna+GP set up is ordinarily quite reliable if the solution statistics are good. By getting duplicate solutions on two days, there is a demonstration of solution quality in the repeatability and some redundancy to test the weights assigned to the two positions, one for each day, when they get adjusted in Star*Net with the rest of the GPS vectors connected to the control points positioned via OPUS.
The default solution for Day 179 looked just fine. It used the CORS sites TXSA (San Angelo), JCT1 (Junction), and TXLL (Llano) at distances varying between 75km and 121km. The solution was from more than 7hrs of observations, and the statistics looked good, so that was great.
On Day 178, however, there had been thunderstorm activity on the far horizon for much of the day and the initial solution that OPUS returned using the default CORS sites looked terrible. It wasn’t survey quality and couldn’t be used. The stations that had been selected were evidently in the weather pattern.
After examining other solutions using various other combinations of CORS sites, it looked as if they were also in the weather pattern. So I got bold and selected some more distant CORS sites, TXSN (Sanderson) and TXOE (Odessa) at 295km and 255km respectively. Those returned a solution with good statistics and with a position that was in essential agreement with that from Day 179.
In an ideal world, we’d have the map of the CORS sites superimposed on a weather map to see what the prospects were. In the real world, it’s damn handy to have more than enough data for an OPUS solution.
Log in to reply.