Yesterday's session only had 3 failed vectors out of 114. Pdop was between 2 and 5 (all dop factors included). Today, with Pdop substantially the same, we had 12 of 44 vectors failed. Some from original initialization, some from a re-initialization. Good SV visibility. The only thing I can suspect is the amount of radio,microwave and radar equipment on site (even though I don't think wuch was in operation)
I merged the ascii files together and imported into SurvCad to analyze. The site, including placement of radio type testing equipment is generally situated in a North South direction. The points from failed vectors make a general East West pattern. One section across the tract on the North side of where we stopped today had no failed vectors. Several sections on the South side from yesterday had none. I'm not sure whether to assume we have isolated a bad section on this tract, as related to gps work, and continue kinematic attempts, or scrap the whole thing and do conventional topo. Wet nasty weather and client is getting a bit impatient.
Any suggestions?
Incidentally, these failed vectors today were spaced as follows: 17 good, 7 failed, 13 good, 5 failed, 2 good.
Thanks
J.D. Billings
J.D.
Email this data set to me. I would like to examine it to see if I can determine what may be happening.
Bill Martin
Ashtech Precision Products
Bill,
I will email the files containing the kinematic data. After continued analysis I believe that during this time we had only 5 SV's available during these periods. From the sky plot, and the dop plot (showing Pdop at 5 or below), I'm not sure if this could be entirely the problem. More developements during a static session yesterday.
New Developement:
I set up a unit on a static point (our main control point that was established from very lenghty observations last month) and turned it on. The battery light came on green, the satellite light came on red. Satellite indicator stayed red with no blinks for at least a minute. I turned the unit off and tried to re-start. Same results. I moved to a different site and turned the unit on and had lock on eight satellites within less than a minute. The main control station is in the near vicinity of the clients receiving/transmitting building. This building is a "sub-station" a couple of miles from their main complex. As I said in earlier posts, this client builds transmitting and receiving antennaes for large commercial clients as well as the military. After having the problem with the receiver not even getting lock on a single satellite, I was informed by an employee of the client that they were, and have been, testing what he described as "an L1 military frequency". No more info could be given.
I still think that most of the problems we are encountering may be due to some really noisy signals, not from the SV's, but from distortions caused by the clients line of work.
Any thoughts on the subject?
Thanks
J.D. Billings
We do some work in and around military installations. The military uses a lot of electronic gadgetry that can mess with GPS observations. It almost requires that you watch each receiver and pay attention to SV lock and signal to noise ratios.
When the G.I.'s fire up those generators I know that I am just about to be in trouble.