GEOG 862
GPS and GNSS for Geospatial Professionals

Lesson 1 Overview

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Overview

About 25 years ago, I read in a trade publication about an event that might have seemed unremarkable to many at the time. A company in the Northeast had agreed to sell the Macrometer to a company in Houston. I was exhilarated. I immediately wrote to the company in Houston and said, “Now that you have the Macrometer, you will undoubtedly need people to operate it. Virtually no one knows anything about it, including me. So you will have to train whomever you hire. How about training me?”

I will always be grateful that they agreed to do so. So, in a matter of months, I found myself leading a crew that did work around the world with the very first operational GPS receiver, the Macrometer.

The Macrometer was a codeless receiver. There are no receivers today that use that particular approach. Most utilize both the code and carrier from the GPS signal. Do the receivers you have used track both? Many consumer grade GPS receivers are code-phase only. Is that an advantage or a disadvantage when it comes to accuracy? You will learn the answers to these questions and many more in the first lesson of this course.

Objectives

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

  • demonstrate understanding of the basic GPS signal structure;
  • discuss the similarities between GPS and trilateration;
  • describe the pertinence of the navigation code;
  • explain the structure of the P and C/A codes;
  • define the creation of the GPS modulated carrier wave;
  • identify the two GPS Observables;
  • describe the role of autocorrelation and the lock and time shift associated with GPS pseudoranging;
  • recognize the pseudorange equation (This is code phase);
  • discuss the role of carrier phase ranging in high accuracy GPS.

Questions?

If you have any questions now or at any point during this week, please feel free to post them to the Lesson 1 Discussions Forum. (To access the forum, return to Canvas and navigate to the Lesson 1 Discussion Forum in the Lesson 1 module.) While you are there, feel free to post your own responses if you, too, are able to help out a classmate.