Space geodesy and the future of land surveying

—by Robert S. Jones, R.L.S.

Looking out the window while flying over the Midwest on a clear day, one cannot help but notice the rectangular grid stretching beyond the horizon in every direction. It is the grand and visionary framework that for the first time in history allowed for wholesale transfer of land rights to common individuals. My family took possession of land in North America very early during this process. They settled on James River, Virginia, in the 1600s and in 1779 traveled in flat boats down the Ohio River with Colonel George Rogers Clark to what is now Louisville, Kentucky. From there they continued to move west, passionately obtaining patents in the newly sectionalized lands. Today the drive to own land persists unabated. The prevailing American dream is still to own land for a home or business, whereupon much of the economy for the land surveyor and survey equipment/software manufacturer rests.
My great, great grandfather, who relayed the Jones family history, was not a surveyor but he understood the grid and how it defined his time and place in the universe, and how it allowed him and his forbearers to take possession of the land. He signed his history, my history: William Richardson Jones, Section 4, Adams Township, Wapello County, Iowa.
Fifty or so miles northeast of Wapello County, and just outside North Liberty, Iowa, and literally within a stone’s throw of the Continuously Operating Reference Station (CORS) NLIB operated by the Jet Propulsion Laboratory at Caltech, is a 240 ton, eleven stories tall, liquid-nitrogen-cooled radio telescope that defines our time and place in the universe.
The North Liberty radio telescope is one of ten telescopes between Saint Croix in the Virgin Islands and Mauna Kea on the Island of Hawaii, which constitute the Very Long Baseline Array operated by the National Radio Astronomy Observatory (NRAO).
The North Liberty radio telescope participates with other radio telescopes around the world in making simultaneous observations of the same objects within and outside our galaxy. These observations are called Very Long Baseline Interferometry (VLBI).
VLBI is one of four space geodesy techniques, the others being Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS), Satellite Laser Ranging (SLR), and the more familiar Global Navigation Satellite System (GNSS). These techniques realize and maintain the International Terrestrial Reference Frame (ITRF).
The National Geodetic Survey (NGS) monitors and maintains our National Spatial Reference System (NSRS) relative to the ITRF to within millimeters. The NSRS is, of course, accessible through the data collected and maintained by NGS from the over 1,000 National and Cooperative CORS covering the United States.
The founding fathers and early surveyors could never in their wildest imaginations have contemplated radio telescopes and the universe they reveal, or the ultra-accurate spatial reference frames they realize and maintain.
If they had access to such science and technology, they would very likely have forgone the chain and established the grid with reference to a quasi-inertial reference frame (e.g., the International Celestial Reference Frame (ICRF)) realized by ongoing VLBI observations of 600 or so extragalactic radio sources at the very edge of the observable universe.
If they had done so, the economy of the land surveyor would most certainly be very different than it is now.
With regard to Wapello County there would probably have been none of those early claim difficulties, and we would have had no need of claim committees to arbitrate with finality disputes between those who first obtained land patents.
One of the greatest challenges land surveyors will increasingly face is the inexorable expansion of global high-accuracy positioning techniques into their everyday work, propelled there by space geodesy and its ability to tie surveys to an extremely accurate and very long-term, continuously maintained global reference frame, the ITRF.
The long-term perpetuation of ultra high accuracy, global positioning will directly and profoundly impact one of the most sacred precepts of our society—land ownership—and how this ownership is established.
If space geodesy were inaccessible or expensive to utilize, then surveyors could rightly take little notice of it and proceed as usual, secure in assuming that the spatial revolution could never force its way into the backyards where they hack and dig in the hopes of finding that all-important pipe in the ground. But, the products and results of space geodesy are fully and easily accessible and not at all difficult to employ by any surveyor operating GPS!
Given the types of individuals who have traditionally become land surveyors, it may seem natural to give the profession a pass on space geodesy. Fortunately or unfortunately, depending on your circumstances, technology waits for no one.
How land surveyors utilize space geodesy may determine whether they remain members of a profession or become, over time, something less as the economy for land survey services slowly changes and reaches a point of no return. Once a technology has taken hold there rarely is, if ever, a way back.
Surveyors who own GPS equipment and who have access to the Internet—the vast majority—have all they need to tie their work to the NSRS and the ITRF and perpetuate locations with high accuracy long after their life times.
It is not necessary to understand correlators, complex visibilities, Fourier transforms, or fringe fitting. It is not necessary to even know that they have anything to do with VLBI. It is merely necessary to be aware of space geodesy—the ITRF, and the NSRS—and to have an aptitude for simple spatial concepts. The software you have right now will do the rest.
It is also necessary to fully embrace and hold in the highest regard that aspect of the profession of land surveying that aspires to the highest attainable art of measurement. For every land surveyor, the art of space geodesy is literally within grasp.
It has been an uphill battle to educate my immediate colleagues about GPS (which may be an anomaly), let alone about space geodesy and the impact it is having on their surveys, as well as the impact this will have on their repeat work. Nevertheless, slowly but surely, some of them are beginning to take notice. Some are even beginning to agree with me. Still there are barriers.
When I succeed in getting my fellow project managers together for a little education and discussion, the first bottleneck is always accuracy. Incredulity sets in when surveyors (for whom closing out within two tenths of a foot in a traverse of a quarter section is very good) are told that they can close out vectors between CORS stations separated by 800 miles to within one hundredth of a foot. This fact does not seem to “penetrate” even in the face of repeated direct evidence.
Another sticking point seems to be spatial abilities and awareness of basic concepts from physics and the earth sciences. To be part of the high accuracy spatial revolution one needs a basic conceptual understanding of map projections and vectors defined in three-dimensional, earth-centered reference frames. It requires an appreciation of gravity fields and accelerated systems, and an awareness of crustal dynamics.
It is not however necessary to understand complex derivations or harmonics. For the most part, simple 3D visualization is adequate. This should be easy enough. After all we are not dealing with a highly abstract infinite dimensional Hilbert space. Again, your software will do the heavy lifting.
As most surveyors know there is immediate economic benefit to space geodesy—which includes GPS. Employing rapid static GPS to run sections and set horizontal and vertical site control is obviously a lot faster than with a total station, and it is arguably faster and certainly more accurate than RTK (several hundredths of a foot at the ninety-five percent confidence level). And the kicker is it can be done by technicians who need only know how to plumb a tribrach or a fixed height pole and push an on/off button.
In the office, a trained operator can link to the CORS, post process, and adjust up to four projects an hour. Trimble Geomatics Office allows data export options to be created that include every type of information one could ever want to attach to a point for inclusion in centrally maintained databases, including metadata.
Unless network RTK becomes considerably more accurate than it currently is, the global spatial revolution for surveyors will probably not be driven by real-time networks but, rather, by high-accuracy, independent, redundant closed vector rapid static GPS within the target-rich CORS infrastructures created for network RTK.
It will be driven by ubiquitous, very low cost L1\L2 receivers that may ultimately be bundled to Internet services for spatial data management.
It will be driven by a society that will eventually expect and then demand that land surveyors tie their work to global reference frames with standardized documented accuracy and redundancy, and then submit that information to public databases accessible over the Internet to everyone.
The profession of land surveying has moved forward by only doing what is required to produce a product viewed more or less as a commodity by individual clients who perceive no value in the survey next door.
As technologies penetrate the profession and are taken up by progressive companies to reduce costs and provide competitive advantage, less progressive companies will have to follow. Should society as a whole turn around and discover that costly surveys and resurveys, boundary disputes, and title issues can be minimized by a spatial revolution, then many surveyors will have to do what they have always done so well—which is to do only what is required to produce a survey. But from that point forward, the economy of the land surveyor will be radically altered.
A typed transcript of the history set down by William R. Jones has been passed to members of my family since I was a child. I occasionally put my hands on it to reassure myself that I have not forever lost his words. Imagine my surprise while researching Wapello County to discover the history on the Internet, along with the histories of other families living there in 1887. At that moment the Web—and space geodesy—became more personal.
What had always been a matter of pride within our family—our land, my great grandfather’s house, our business—was now part of the information superhighway to which space geodesy contributes hard data.