I am experimenting with an L1 receiver and was wondering is it feasible to establish control points for small topographic surveys using just one L1 receiver and data from one CORS, post processed in GNSS solutions. I would like to use it on baselines up to about 20km. I have seen reasonable results so far with about an hour on each point but would like to get the opinion of those that have more experience in this area as my experience so far is limited.
Time, you always want to let it cook for longer than you think.
I had great results with our old L1 pair with a minimum of 45 minutes common occupation with baselines less than 6 km. I would leap frog loops and close usually within 0.01' HZ and 0.01' per setup VT. We were usually tying into traverses so we had a check.
How close does your control need to be for these surveys?
Two L1s are better because simultaneous observations are better.
I suggest you observe three points on the job that you can traverse through. At 20 km 45 minutes should be OK but since you are new start with 1 hour. Also consider how long it takes to do the field work for the small topo and during all that time have a few points being occupied by your L1 receiver.
Assume you are doing three control points and you have a fixed height rod and a three legged bipod, so your setup times are fast. 20 minutes on each point twice around and the solutions will be almost the same as if you had occupied each point for an hour and a half because of the change in the constellation. Be aware of the PDOP and number of satellites during those short spans. It is possible to have short periods of poor PDOP due to few satellites and poor constellation geometry every day. With shorter observations it is much more important to do planning. If that bad GPS time is one of your observation times your solution will suffer. If I knew I was going to have one of those times I would make sure I was setup 10 minutes prior to the dropoff and waited for 10 minutes after it got better. Poor PDOP in the middle of an observation does very little harm. The other choice is to go to lunch.
Paul in PA
spledeus, post: 342901, member: 3579 wrote: Time, you always want to let it cook for longer than you think.
I had great results with our old L1 pair with a minimum of 45 minutes common occupation with baselines less than 6 km. I would leap frog loops and close usually within 0.01' HZ and 0.01' per setup VT. We were usually tying into traverses so we had a check.
How close does your control need to be for these surveys?
For these kind of surveys my relative accuracy of control would be about 5mm Horizontal and 5-10mm vertical from total station work. The absolute accuracy on the grid I would be looking to achieve around 10mm and 20mm respectively. Is that doable on a regular basis with just the one receiver. I am achieving around it so far with about an hours observation time on each point. The vertical can be a bit higher though sometimes. This is checking off national benchmarks and my own control.
Paul in PA, post: 342937, member: 236 wrote: Two L1s are better because simultaneous observations are better.
I suggest you observe three points on the job that you can traverse through. At 20 km 45 minutes should be OK but since you are new start with 1 hour. Also consider how long it takes to do the field work for the small topo and during all that time have a few points being occupied by your L1 receiver.
Assume you are doing three control points and you have a fixed height rod and a three legged bipod, so your setup times are fast. 20 minutes on each point twice around and the solutions will be almost the same as if you had occupied each point for an hour and a half because of the change in the constellation. Be aware of the PDOP and number of satellites during those short spans. It is possible to have short periods of poor PDOP due to few satellites and poor constellation geometry every day. With shorter observations it is much more important to do planning. If that bad GPS time is one of your observation times your solution will suffer. If I knew I was going to have one of those times I would make sure I was setup 10 minutes prior to the dropoff and waited for 10 minutes after it got better. Poor PDOP in the middle of an observation does very little harm. The other choice is to go to lunch.
Paul in PA
Sounds like a reasonable way of working. I have generally been leaving the receiver running while I am on the robot.