Our understanding of the world around us is directly related to our technological capabilities. Most mythology that comes out of ancient civilization is simply the result of people from the time trying to explain phenomena that were, based on what was available to them, unexplainable. As our technology improved, so did the realism in our explanations, and it’s an ongoing process. While the things more recent generations have gotten wrong aren’t as fantastical as what our ancient counterparts came up with, new discoveries are still constantly shifting our understanding of the planet.
An example of this happening today can be found in the United States’ surveying community, as the National Geodetic Survey (NGS), part of the National Oceanic and Atmospheric Administration (NOAA), is currently in the midst of a truly massive project to modernize the National Spatial Reference System based on (relatively) new insights about our world. This work has been going on for years now – though good luck finding an exact start date, as you’ll get different answers depending on how and who you ask – but we’re approaching the finish line for the bulk of the work.
With that in mind, we’re going to be highlighting different pieces of this work periodically throughout the rest of this year, speaking with those doing the work, including team members at NGS as well as at Oregon State University, who is also assisting with the project. To start today, we’ll be taking a broad look at the modernization overall, including why it’s happening, how it’s happening, and what the results will be. To delve into the issue, Geo Week News spoke to Galen Scott, a Constituent Resources Manager with NGS who refers to his job as being a “Geek Translator,” as well as Dr. Chris Parrish, a professor with Oregon State’s College of Engineering and Director of the Geospatial Center for the Arctic and Pacific (GCAP).
It’s worth starting with why this effort is happening in the first place, and what the modernized spatial reference system will replace. The answer to that second question is primarily what is known as NAD83 and NAVD88, the current horizontal and vertical reference frames, respectively. That actually leads into one of the major changes with this modernized system, too: There will no longer be separate horizontal and vertical systems, but rather an integrated system in which the dimensions “work together,” according to Scott.
Pushing things back just a bit, Scott relays that, at least in some sense, the idea to start modernizing this system goes back to almost immediately after NAVD88 was released. This was in 1991, and shortly after was when GPS started to become functional and used for military purposes. In that time, scientists from NGS effectively figured out how to get around “selective availability” initiatives put in place around GPS, which essentially opened GPS up to the broader surveying community. The result was a broader understanding of the world around us, as alluded to at the top, leading to knowing we needed to make adjustments.
“The relationship between the type of heights in NAD83 (ellipsoid heights) and the type of heights in NAVD88 (orthometric heights) is a really simple equation, and works perfectly if both datums are free of systematic errors. Unfortunately, that equation doesn't often work well in the case of NAD 83 and NAVD 88, partly due to systematic errors in NAD 83 and partly because of the old data in the geodetic leveling network – NAVD88 – was comprised of 80 years of geodetic leveling that was all adjusted together with the assumption that nothing had moved,” Scott said. “Of course stuff had moved, but it was the best we could do at the time; it was the best technology. But that idea of a GPS ellipsoid height, a geoid model, that’s what really came out of it, and that’s why we’re moving to a new system, because we’re now defining that new system through GPS ellipsoid heights and a new gravimetric geoid model, called GEOID2022.”
In terms of how this work is done, the geoid model is based heavily on gravity, and for that you need measurements from the ground on up. Scott said, “Gravity is a funny thing. You need observations on the ground, going out into space. Historically, we’ve had terrestrial gravity measurements for a long, long time. We’ve had satellites that have been up there for a while that give us satellite-based measurements. But what we needed was the middle portion of the gravity field, or airborne gravimetry.”
That’s exactly what NGS has been working to collect over the last 17 years with their GRAV-D program, for which they’ve been flying throughout the entire United States and its territories to collect gravity data throughout the nation. Scott relays that the work just finished up, with 100 percent of the original goal being completed in February of this year.
It’s important to note that this work doesn’t need to be done immediately lest we suffer grave consequences. There are some consequences we could be facing in the short-, medium-, and long-term by sticking to the current datums, but the current frames “are just fine for many of their intended purposes,” according to Scott. “The fact of the matter, though, is the technology has changed, and we can do better, and we should do better.”
Scott goes on to note that so much of our world – more than any other point in our history – is tied to spatial and location data. Accuracy is key, and with a system that doesn't take into account any movement of the Earth, inaccuracy will inevitably grow over time. That said, there are some potential issues apparent today. Scott notes that in the Gulf region of Texas, for example, floodplain mapping is crucial, but on-the-ground reference points haven’t always been up-to-date. It’s easier to get those points up-to-date, though, with GPS-based surveying.
Dr. Parrish also spoke to this, reiterating that potential issues would only worsen over time. For example, he says, things like lidar point clouds may not be accepted because the software would recognize the reference frame inconsistency. He also noted some potentially larger issues. As an example, he notes that container ships continue to get larger, and just centimeters of draft (the depth of a vessel below the water) can be the difference between thousands of dollars of cargo. Therefore, shipping companies want to have as large of vessels as possible to maximize their loads, which in turn means we need to have highly accurate depth levels of these channels to ensure large vessels can navigate.
Dr. Parrish is leading the team at Oregon State and GCAP, who are one of four institutions – along with Michigan State University, Ohio State University, and the Scripps Institution of Oceanography – selected to help advance this modernization effort from NGS. The institutions weren’t necessarily selected due to regional affiliation (two of the four institutions are from the Midwest, for example), but Dr. Parrish did note that the Pacific Northwest is particularly interesting in this respect given the tectonic activity along the Pacific Rim of Fire.
Over the course of the next few months, we’ll be diving deeper into the work being done by Parrish and his team, with commentary from both that team and those at NGS who are doing similar work for the entire nation. This will include looking specifically at some of the work for this around hydrology, technical looks at GNSS-based projects, some applications and datums, and a crucial piece of the puzzle around outreach and education.
