Leadership Talks - Signaling a Shakeup

August 1, 2007 By: Tracy Cozzens GPS World

Interview with Ken Hudnut, U.S. Geological Survey

Ken Hudnut (KH), U.S. Geological Survey geophysicist and leader of the Southern San Andreas Fault Evaluation (SoSAFE) Project, spoke with Managing Editor Tracy Cozzens (TC) on June 28.

Ken Hudnut uses GPS to locate a boulder offset 560 meters by the San Andreas fault

TC: Can you give us an update on the L1C finalization and approval process?

KH: L1C has been specified in a document called the IS-GPS-800, and the initial public release of that was in April 2006. So we're now over one year through the public review process called the Interface Control Working Group (ICWG). That's a formal process whereby the GPS Wing, through a Federal Register announcement, asks for public input from the international GPS user community. And that formal process of accepting and handling comments is nearing conclusion. So all public comments that have come in have been addressed in the current version of this IS-GPS-800 document. Interested people can find the document online at the GPS Wing website.

The IS-GPS-800 specifies all details of L1C signal design, and that's in common with the earlier interface control documents for other GPS signals. That makes it so that people can begin designing receivers today, well in advance of launch. That's the whole idea, to make it so that signal designs are entirely open and entirely specified for manufacturers and other users and stakeholders so that they can see every detail of the signal design.

This "ShakeMap" of estimated seismic ground-shaking intensity shows the San Andreas Fault during a Big One scenario, a magnitude 7.8 earthquake. California is heavily 'wired' with GPS stations that measure plate motion.

That review process is basically wrapping up and the intent of the GPS Wing is to move forward. They would like to get everything pinned down on GPS Block III before going out for the next stages of their acquisition and procurement process.

TC: When do you think we can expect the first Block III launch?

KH: People have been saying for some time now that initial launch of Block III would occur in August 2013.

TC: How long thereafter until L1C is operationally useful?

KH: It's a gradational thing, and I think the anticipated rate of satellite launch would be at three per year, optimistically. So IOC (initial operational capability) would be expected about five years into Block III, around September 2018. IOC to FOC (full operational capability) is also gradational, but FOC would be in the neighborhood of 2021.

TC: At either stage, you'd still be able to make use of the signal.

KH: Yes, so as soon as a new signal is introduced, people are going to start jumping on it and using it. One example of that is L2C, which is currently being broadcast and received, and people are starting to make use of it. As more and more satellite signals are introduced, GPS becomes more and more useful. L2C is significant because it gives civilians a signal on L2 that they can legitimately use, so that's a plus for civil users. Having that L1/L2 combination is very powerful for civil users. In the future with the introduction of L5, it will allow us to do tri-laning, which we are also looking forward to.

This map represents the Plate Boundary Observatory, funded by the NationalScience Foundation and built by UNAVCO, which increases the accuracy of real-time earthquake, volcano, and tsunami alerts.