[LEAPSECS] GPS certified for navigation?

[Jonathan E. Hardis]

On Sep 23, 2010, at 3:35 PM, Steve Allen wrote:


> for robustness against the ionosphere (mostly for surveying) see WAAS

> http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System


As the link makes clear, WAAS is funded by the FAA "for aircraft," not  
"for surveying."

Aircraft and surveying have opposite needs in GPS augmentation  
systems.  For aircraft, the primary issue is prompt warning if  
something went flakey on the GPS signal. For surveying, the primary  
issue is achieving cm-level horizontal resolution.  To do that,  
surveyors use "real-time networks" of monitoring stations at fixed  
locations.  Many of these are local and cooperatively organized, like  
the ones in Washington State (http://www.prsn.org/) and Oregon (http://www.theorgn.org/ 
).  With a communications channel from the network to the surveying  
site, cm-level resolution can be obtained in real time.  Otherwise,  
the surveying data can be post-processed.  Compared to the needs of  
aircraft (collision avoidance), surveying is much more fault-tolerant.

    - Jonathan