Precision Geo-location Services Evolved with GPS System
SOURCE: Lee Ott, OmniSTAR, Inc., “Meeting the Challenges of Nature: The Impact of Space Weather on Positioning Services: Solar Cycle Progression and the Maturing of GPS,” presentation to the space weather workshop, May 22, 2008.
As an example, OmniSTAR provides differential GPS corrections to users that buy their own GPS receivers. As Lee Ott noted, “Our strategy is to give enough information to the user so that the user at his current location can make the appropriate decision about whether or not his positioning is accurate. He can make that decision himself.” This approach is important because in the diverse community of GPS users the needed level of accuracy varies.
GPS signals originate from satellites that are at about 12,000 miles altitude, and these signals have to pass through the ionosphere in order to reach GPS receivers on the ground (see Figure 5.7). The GPS signals are degraded in several ways by severe space weather. When the density of electrons and ions in the ionosphere increases in response to solar flares, the propagation delays (time delays) change, the paths that the GPS signals follow are slightly distorted (bent like light is when it passes from air to water), and the strength of the GPS radio signal is weakened. The consequence of the distortion is that the GPS receivers miss a user’s exact location. Such errors in location can have very significant effects on the operation of deep-ocean drilling platforms, for example, because if the errors are too large, the platform could move off its intended position, causing a drill line to break. And if the signal weakens sufficiently, the GPS receiver might not be able to provide the necessary location. An example of the signal fade that occurred during a significant solar flare event in December 2006 is shown in Figure 5.8. As noted by Ott, “Once [deep-ocean drilling platforms] are on station and sitting in maybe a thousand feet of water and drilling a hole, the cost of that rig is about a million dollars a day. If they are drilling a hole and something eventful happens and they lose their positioning, they have to do an immediate disconnect. The only way they can do it [is to use] blowout preventers, which basically are big scissors that just cut the pipe off. So