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Precise Geodetic Infrastructure: National Requirements for a Shared Resource
by agencies of the U.S. government and by GNSS/GPS equipment manufacturers.4 In addition to broadening the accessibility of the infrastructure, these standards enable the scientific research that has led to the order-of-magnitude per decade improvement in geodetic accuracy. As the goal now shifts to applications that require improved spatial and temporal resolution with low latency (real-time geodetic imaging), the demands on the geodetic infrastructure and the importance of universal standards will continue to increase. Many potential future breakthroughs, like fully autonomous transportation systems, are possible only with a highly robust geodetic infrastructure that provides accurate data products in real time in a universally accepted reference system.
As famously stated by Niels Bohr, “[p]rediction is very difficult, especially about the future” (Ellis, 1970, p. 431). Nonetheless, it is legitimate to ask whether the order-of-magnitude-per-decade performance improvement rate for precise geodesy is sustainable in the foreseeable future. Although it is questionable whether improving the ITRF to achieve a millionth of a meter accuracy is a sensible question, it is certainly clear that there is much room for advancement in space and time resolution for geodetic data. The challenges to achieving real-time geodetic imaging, however, are readily apparent. Consider doubling the horizontal resolution of any geodetic data set and updating it twice as often as in the past, and it is soon realized that this calls for acquiring, storing, processing, and analyzing eight times as much data. If users desired to improve the spatial resolution of the commonly used SRTM digital elevation datasets from 90 meters globally to 10 meters, they would have to be ready to deal with a dataset approximately 100 times larger. If capturing changes with time is of the essence, this factor can easily grow to be 1,000 times or more. Improving the vertical accuracy from 15 meters to 1.5 meters would not directly impact the data set size, but the information needed to generate the data set would increase by another factor of 100 to 1,000. With these improvements, data volumes could grow by a million-fold compared to today’s volumes. The fact is, LiDAR imaging of critical areas such as coastlines or earthquake faults is already pushing well beyond these limits in all four dimensions (see Wdowinski and Erriksson, 2009).
Perhaps further into the future it may be feasible to deploy very large (100-meter inflatable) radar antennas in geosynchronous orbit, permitting real-time InSAR imaging of the Earth’s deformation on a continental scale (“InSAR everywhere all the time,” Zebker, 2005). We also can imagine a steady microwave illumination of the Earth’s surface from geostationary or even lunar radar transmitters. With superior time transfer capabilities, bistatic radar imaging becomes possible: small inexpensive receivers in low Earth orbit could image the Earth’s surface interferometrically, much as optical sensors image the sun-illuminated surface now, except that this would be an all-weather capability.
The applications reviewed in this section represent just a few of the current and future benefits of the geodetic infrastructure. Of course, it would not be unexpected if any predictions, short- or long-term, were far outstripped by reality. As the technology continues to mature, it becomes ever more accessible to an increasingly wide group of scientists, engineers, and entrepreneurs. Developers and users alike will increasingly be able to take advantage of geodetic methods, techniques, and systems without specialized knowledge of geodesy or related fields.
All the advances reviewed in this chapter are and will be made possible by an underlying geodetic infrastructure that is robust, reliable, and accurate. This infrastructure includes not only measurement systems and networks discussed in Chapters 3–5, but also the global services that analyze and maintain standards for these systems, as well as the analysis that knits together these systems.
Providing the infrastructure capable of supporting the societal needs of today and the future is the great challenge for the field of geodesy. In the next section, the committee provides recommendations for meeting this challenge.
The NGS and the Federal Geodetic Control Subcommittee develop federal standards for geodetic control surveys.