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correction on an earlier post about WAAS
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alange
Posted 6/12/2007 21:24 (#161641 - in reply to #161566)
Subject: Re: correction on an earlier post about WAAS


Sunnyvale, CA
The difficulty with getting good L1-L2 measurements in a user receiver is related to the very noisy character of the L2 measurement which does make the L2 measurement somewhat of a guess compared to the L1 measurement. However, if proper attention is paid to the details of making a good L2 measurement, and you don't have a multipath problem at the receiver, the results for a single L1-L2 receiver are likely better than using an array of reference stations with an interpolated iono model designed for use over an entire continent (like used for WAAS). The array of reference stations does have something going for it, however. There is a reduction in multipath interference when you have good geodedic antennas at the reference stations and there is an averageing of the noise with multiple reference receivers. Over the area covered by the base stations there are variations in the ionosphere that make the Wide Area DGPS correction less accurate, for example, when your reference stations are spread out over the continent like the WAAS reference stations. If you had a smaller network of reference stations, for example, 50 to 80 km spacing with a well designed ionosphere model, you would have a good chance at doing better than a single receiver would allow. In fact, you would be able to do RTK over a large area with that kind of reference network, because what usually limits the range for RTK is the ionosphere decorrelation becomes too large at 10 to 15 km to resolve the integers.
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