Anyone ever study what effect multipath has on static sessions?

In the past I've set up static recievers in questionable locations, and found that the vectors either processed fine and reported fine, or failed and reported as failed. I've never had a vector reported as "passed", which didn't have roughly the level of accuracy displayed in the adjustment stats. And, I know this because any questionable GPS point has been shot with a total station.

With that said, is multipath truly a problem with L1 static observations? With observations being 30 minutes+, wouldn't the movement of the satelites change the deflected multipath signal enough so that processor would either recognize and through out the bad data, and process vectors without it, or not be able to process it all, if enough good data was not available?

Based on what I've seen, multipath is not as much of a issue for long static observations as it would be RTK or maybe even fast static, where the satelite motion is not as great per observation.

Is this a true statement? I'm hoping some of the experts have studied this can comment on it.

-Greg
Modified By Greg Shimp on 6/10/2001 at 11:20 AM

I remember reading in a Trimble 4800 manual that the minumum time to occupy a station with RTK was 15 minutes to "avoid" multipath, (although this is twin frequency to initialise but L1 after), the idea was as much TIME as possible as the sats change.

The ICSM "STANDARDS AND PRACTICES FOR
CONTROL SURVEYS(SP1)" recomends 22 minutes per station (from 2 independant base stations at 10 minutes each occupation, and 20% of all stations from a third base.)

The reason was once again the TIME factor.

Trimble 15 minutes, ICSM 22 minutes - makes the 30 minutes look good!!

Greg,
Multipath is less of a problem with long observations because the multipath changes over time (the satellites are moving) and tends to average out. You're correct in thinking that multipath effects are more severe for short occupations (kinematic or RTK).
---Brian