National Academies Press: OpenBook
« Previous: Oceanography
Suggested Citation:"Findings." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×
Page 51

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

GPS APPLICATIONS AND REQUIREMENTS 51 alone, unless SA is eliminated and other improvements are made to increase the accuracy of the SPS. Geodynamics Despite improved post-processing software and the use of differential GPS, the effects of A-S and SA degrade the results by 50 percent or more, primarily through the loss of the signal-to-noise ratio using dual- frequency codeless receivers. The loss can be partially recovered by replacing existing receivers that are a few years old with newer equipment. Significant savings in time and costs would occur, however, if this was not necessary. Airborne Geophysics SA has little effect on airborne geophysical applications when differential GPS and post-processing are utilized. As with geodynamic applications, however, the presence of A-S greatly reduces the signal-to-noise ratio available to dual-frequency receivers. The dynamic, high-multipath environment that exists for GPS receivers on aircraft makes codeless receivers especially vulnerable to losing lock on the L2 signal and requires a lengthy reacquisition time. In lieu of code-tracking capability on L2 or an alternative L-band signal, improvements to the tracking loops in codeless receivers could improve this situation.39 Findings Using post-processed GPS orbits provided by the IGS network of differential reference stations, the effects of SA can be eliminated for most Earth science applications, and with the use of dual-frequency "codeless" receivers, centimeter-level positioning accuracies can be achieved. The availability of a second GPS frequency for civil use with unencrypted code would greatly enhance many Earth science applications that require high-precision accuracy. Dynamic, high-multipath applications, such as airborne geophysics, would benefit from faster acquisition and more robust tracking. Applications such as remote atmospheric sensing require submillimeter precision in the carrier-phase observables, which may be achievable using a second unencrypted signal. 39 The effects of SA and A-S on the use of GPS in airborne geophysics are discussed in more detail in the NRC report Airborne Geophysics and Precise Positioning: Scientific Issues and Future Directions, Appendix A: Effects of Selective Availability and Anti-spoofing.

Next: Current and Future Applications and Requirements »
The Global Positioning System: A Shared National Asset Get This Book
×
Buy Paperback | $61.00 Buy Ebook | $48.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

The Global Positioning System (GPS) is a satellite-based navigation system that was originally designed for the U.S. military. However, the number of civilian GPS users now exceeds the military users, and many commercial markets have emerged. This book identifies technical improvements that would enhance military, civilian, and commercial use of the GPS. Several technical improvements are recommended that could be made to enhance the overall system performance.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!