Aero-Terms!

Aero-Terms are designed to be a daily reminder of the terms, names, acronyms and explanations of the unique language that populates the aviation world. Aerospace, sport aviation, fixed wing, helo, you name it... it's all fair game.

Aero-Terms should serve as a quick but intriguing reminder of the terms you may use every day, or an introduction to an aspects of the Aero-World you may not yet be familiar with. ANN also encourages readers to go beyond the FMI link, and further research any intriguing terms.

Suggestions for future Aero-Terms are ALWAYS welcome, as are additions or discussion of the explanations given for each Aero-Term.

DGPS (Differential Global Positioning System)

DGPS achieves enhanced accuracy since the reference and user receivers both experience common errors that can be removed by the user. Position errors less than 10 meters are typically realized.

In the basic form of DGPS, the position of a reference receiver at a monitoring or reference station is surveyed in, that is, its position is known accurately. The user receiver should be no more than about 300 miles away from the reference receiver which makes pseudorange measurements, just as any user receiver would. However, because the reference receiver knows its position accurately, it can determine “biases” in its pseudorange measurements. For each satellite in view of the reference receiver, these biases are computed by differencing the pseudorange measurement and the satellite-to-reference receiver geometric range. These biases incurred in the pseudorange measurement process include errors arising from ionospheric delay, tropospheric delay, and satellite clock offset from GPS time. For real-time applications, the reference station transmits these biases, called differential corrections, to all users in the coverage area of the reference station. Users incorporate these corrections to improve the accuracy of their position solution.

For the basic local area DGPS (LADGPS) the position solutions of users further away from the reference station are less accurate than those closer to the monitoring station because pseudorange measurement errors tend to be spatially correlated. This loss of accuracy due to spatial decorrelation can be improved with more sophisticated techniques that fall under the heading of wide area DGPS (WADGPS) such as WAAS.  

FMI: www.faa.gov