Typically, Several companies approach to base station distances differ. Typically, In Europe PPP is well accepted for collection of LiDAR. A lot of Folks are using Terrapos and some folks just use CORS stations. It has been my experience that using base stations still yield the best results. It is a known fact that the closer the base stations to the aircraft the better the result. Recently, some folks have indicated to me that base stations as far as 250km can yield accuracy for 4 foot contour data. I find this troubling because even though the GPS constellation is much better than it was in the 90’s, it still seems that the GPS result is critical to the accuracy of the data. I have seen very good results with GPS solutions up to 80km and even some times up to 100km, but much more than that the result is marginal. For 1 foot contour specifications, 45km is a reasonable. I would like to get feedback from folks on this because we are all over the place in acceptable distances.
Furthermore, Applanix and Leica have recommended length for flight line distances. What is your experience on this? My rule is no more than 20 minutes but I have seen positive results with longer flight lines but not always.
This seems to be the ongoing debate, Currently for 1 foot contours we try and stay withing 18 nm of a basestation but this is definately not the rule. It seems everyone has there own opinion on what is best. I agree on the 20 minute max online time.
FYI – This paper argues for multiple base stations at different elevations in the survey area to best minimize atmospheric induced GPS errors:
Shan, S., M. Bevis, E. Kendrick, G. L. Mader, D. Raleigh, K. Hudnut, M. Sartori, and D. Phillips (2007), Kinematic GPS solutions for aircraft trajectories: Identifying and minimizing systematic height errors associated with atmospheric propagation delays, Geophys. Res. Lett., 34, L23S07, doi:10.1029/2007GL030889