GEOG 862
GPS and GNSS for Geospatial Professionals

Lesson 2 Overview



Biases are fascinating. The frequency standards, the clocks in GPS satellites, run faster than the clocks in GPS receivers, and the clocks in the GPS receivers are much less sophisticated than the clocks in the satellites. During the trip through the ionosphere, the information on the GPS signal appears to slow, and the ionosphere affects L2 more than L1. You might find it interesting that when a GPS signal reflects off a surface before it reaches your receiver, this is called multipath, and, believe it or not, it actually has something in common with a billiard ball (as a billiard ball often bounces off several surfaces before finding its way to the pocket). In this lesson, we will also talk about how GPS surveying is done.


At the successful completion of this lesson, students should be able to:

  • demonstrate biases and solutions;
  • explain the error budget;
  • explain the biases in the observation equations;
  • describe user equivalent range error;
  • identify the satellite clock bias, dt;
  • define the ionospheric effect, dion;
  • recognize the receiver clock bias, dT;
  • describe the orbital bias;
  • explain the tropospheric effect, dtrop ;
  • identify multipath;
  • recognize differencing;
  • differentiate between classifications of positioning solutions;
  • discuss relative and autonomous positioning; and
  • recognize the benefits of single, double, and triple differencing.


If you have any questions now or at any point during this week, please feel free to post them to the Lesson 2 Discussion Forum. (To access the forum, return to Canvas and navigate to the Lesson 2 Discussion Forum in the Lesson 2 module.) While you are there, feel free to post your own responses if you, too, are able to help out a classmate.