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GPS on Bench Marks

Diving Deeper: Episode 60

a person uses a smartphone to look at coordinates on a hike

Where is it?

Bench marks may be hard to spot even if you have the coordinates.


HOST: Today on Diving Deeper, we are highlighting a unique volunteer project. Whether you live along the coast or further inland throughout the United States or its territories, and if you have a GPS device, you can participate in the GPS on Bench Marks project to help validate height information.

Joining us today to discuss this opportunity is Christine Gallagher, the Constituent Resource Manager with NOAA’s National Geodetic Survey. Hi Christine, welcome to our show!


HOST: Christine, to start off today, can you describe what a bench mark is?

CHRISTINE GALLAGHER: Sure, a bench mark is a term we use to describe any permanent mark or disk that’s either in the ground or attached to a large structure. And this permanent mark or disk has a known elevation or height which is why it’s so valuable to us. More colloquially, people use the term bench mark to mean any mark that has latitude, longitude, or elevation information, but we like to call those marks survey marks and reserve the word bench mark for marks that have elevation information.

HOST: Christine, can you tell us more about this GPS on Bench Marks project that your office is leading?

CHRISTINE GALLAGHER: Sure, so NOAA’s National Geodetic Survey is promoting an effort we’re calling GPS on Bench Marks. And the idea behind this project is that we’re encouraging anybody from the public to go out to their area of interest and find bench marks, collect information about the bench marks, and send that information back to NGS because the information you send us could help us improve the National Spatial Reference System.

We’re most interested in having you send us high quality GPS data, but there is other useful information that you could send us including digital photographs and just telling us about the condition of the bench mark that you find in the field.

HOST: So, you noted that this effort will provide data to improve the National Spatial Reference System. What is the National Spatial Reference System?

CHRISTINE GALLAGHER: The National Spatial Reference System is defined by NOAA’s National Geodetic Survey and it is the term we use to refer to the reference frames that define latitude, longitude, and elevation information. The National Spatial Reference System is relevant to people everywhere in the United States and it’s important for mapping, surveying, and really collecting any geospatial information.

HOST: So back to the GPS on Bench Marks project, where are these bench marks located?

CHRISTINE GALLAGHER: There are hundreds of thousands of bench marks actually located across the country. They’ve been installed over the past two centuries. We installed a lot of the bench marks to help us define these reference frames that we use for mapping and surveying today. Some of them are easy to find, they’re found along roadways in your community. Others might be more difficult to find and are in remote locations.

HOST: How does someone find one of these bench marks, if they’ve never seen one before in their community and they’re interested in participating?

CHRISTINE GALLAGHER: I would recommend that people visit the National Geodetic Survey’s website and use one of our map service tools. You can use the NGS Data Explorer to actually enter in your own zip code and find bench marks that are close to you.

HOST: Fantastic. And who can participate in this effort? Is there a certain level of technical expertise that you need to be able to take part?

CHRISTINE GALLAGHER: I think there’s two groups of people that can help us. First, there is just anyone with a GPS receiver or even a GPS-enabled cell phone. They don’t need a lot of expertise. You just have to be interested in finding bench marks in your community and sending us information.

We’re also interested in reaching out to land surveyors, who do have some more experience and they can send us information that can really help us improve some of our models and tools.

HOST: Great. And you’ve talked about this a little bit, but what equipment is needed to collect the data?

CHRISTINE GALLAGHER: For our first group of people, just the general public. You will need a GPS receiver. It can be a hand-held device or you can use your cell phone. Those folks would also probably need to take a digital camera out with them in the field.

For our land surveyors who are joining this effort, you would need a survey-grade GPS receiver.

HOST: Christine, what kind of data are folks collecting for you when they get to a bench mark?

CHRISTINE GALLAGHER: There’s a number of different types of data that people can collect. The general public will probably either be collecting GPS hand-held coordinates, a digital photograph or even a description of the condition of the mark. The hand-held coordinates that anyone with a hand-held GPS device can send us is really important because some of our bench marks do not have highly accurate latitude and longitude information so getting a GPS coordinate is really helpful for making that bench mark easier to find in the future.

A digital photograph is very helpful because it can let people know if the condition of the mark has changed, if the environment around the mark has changed, if there’s a new building, things like that can be captured in a digital photograph and again can make it easier for land surveyors, or others to find the mark in the future.

There’s also an opportunity to just send a written description of the condition of the mark which can be important because marks get disturbed over time. They might be disturbed or destroyed and noting that and sending that information to NGS is very helpful.

Another type of information that can be sent to NGS, and this is directed more at our land surveyors who might be participating, is actually high-quality GPS observations. We’re looking for at least a four-hour data set and then that information would be submitted to our Online Positioning User Service, which we call OPUS.

HOST: So Christine, how do you send the information back to your office, NGS, the National Geodetic Survey?

CHRISTINE GALLAGHER: Once you’ve taken the GPS coordinates or the digital photograph when you’re out in the field, you’re going to have to go back to your home or office and get online and use some of our online tools to submit that data. You can find the tools that you need by going to the GPS on Bench Marks website and we’ve also tried to create some training and held a webinar that you can view to learn more about how you actually use these tools.

HOST: Is this an ongoing effort or are you just looking for volunteers over a specific timeframe, like over the next year?

CHRISTINE GALLAGHER: This is an ongoing effort. We are looking for people to help us improve the National Spatial Reference System over time. We’re particularly interested in improving the National Spatial Reference System leading up to 2022 when we’re going to be making some major improvements. We welcome people to help us at any time. There’s also an opportunity annually to join this effort during National Surveyors’ Week. It’s a time when people in communities coordinate their efforts and there’s a lot of publicity and a lot of opportunities to join this effort. That happens in the third week of March every year.

HOST: Christine, we’ve talked a little bit about how collecting this data gives us information for height and elevation in certain areas. What do we use height and elevation data for?

CHRISTINE GALLAGHER: Height and elevation information is used for any construction project, you know how high your home is, and it is especially important when we’re talking about the way water will flow, so for flooding, risk of flooding, floodplain mapping, which is very important to everyone who owns a home or is trying to cross streets and evacuation routes during storms. Elevation information is important to all of those applications.

HOST: Fantastic and that’s probably why there’s hundreds of thousands of them all over the country because it applies to us all. Finally, Christine, do you have any closing words to leave our listeners with today?

CHRISTINE GALLAGHER: I would just say that I encourage everyone who’s interested to join this effort. I think you’ll learn a lot about what is already existing near your community and you have an opportunity to make the bench marks in your community more valuable, both to NOAA’s National Geodetic Survey and to the land surveyors in your community.

HOST: Thanks Christine for joining us on Diving Deeper and thanks for talking about the GPS on Bench Marks effort. For folks who are interested, you can find more information online at geodesy.noaa.gov/GPSonBM or search online for GPS on Bench Marks. That’s all for today’s show, thanks for tuning in!

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