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DIFFERENTIAL GPS (DGPS) WAAS
DGPS works by placing a high-performance GPS receiver (reference station) at a
known location. Since the receiver knows its exact location, it can determine the
errors in the satellite signals. It does this by measuring the ranges to each
satellite using the signals received and comparing these measured ranges to the
actual ranges calculated from its known position. The difference between the
measured and calculated range is the total error. The error data for each tracked
satellite is formatted into a correction message and transmitted to GPS users. The
correction message format follows the standard established by the Radio Technical
Commission for Maritime Services, Special Committee 104 (RTCM-SC104). These
differential corrections are then applied to the GPS calculations, thus removing
most of the satellite signal error and improving accuracy. The level of accuracy
obtained is a function of the GPS receiver. WAAS is based on a network of approximately
25 ground reference stations that cover a very large service area. Signals from GPS
satellites are received by wide area ground reference stations and used to generate
DGPS corrections.
Differential GPS Broadcast Site
Summary of Contents for RPR 110
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