Re: WAAS correction data
- From: Dale DePriest <Dale@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 03 Sep 2005 16:03:35 -0700
s_anode@xxxxxxxxxxx wrote:
Richard,
The WAAS ground system doesn't correct troposphere error. User receivers use a model to correct troposphere error.
True enough but it manages to remove tropospheric errors from the source so that a receiver model can be used. The standard dgps system does not have this capability. WAAS breaks up the error sources and provides separate corrections for three of them while isolating the others as best it can.
Dale
In single frequency GPS (not using L2) the dominant un-corrected user errors are multipath and the ionosphere delays. The Klobachar model used to correct for ionosphere errors is only a predicted approximation. WAAS estimates the real ionosphere delay at 5 deg lat long increments and broadcast those corrections every 5 minutes. The residual error in the Klobachar model varies with time of day, latitude and the level of disturbance in the ionosphere.
Troposphere delays get very large at low angles of elevation, but the residuals uncorrected by the model are pretty small until you get down below 10 to 15 deg.
Tom
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