I have mentioned in passing that I regularly use GPS in the woods. Today, without going into information overload, I will show some examples of what I do.
There are two basic uses for GPS in the work that I do: navigating to a given location, and storing location coordinates to create maps.
I’m fond of saying that I get paid to walk in the woods. Of course, nobody will pay me unless I give them something useful. My job is to collect specific information about the trees in a given area. Sometimes I also collect information about the land itself; usually that involves determining how many acres of trees are out there.
The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note any observations you have made of the world around you. Insects, weather, meteorites, climate, birds and/or flowers. All are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
|
Most of my current clients already have good maps of their land base. They give me an electronic file that contains the location of each plot that I am to take for them. A “plot” is a physical location on the ground where I gather information about tree species, diameters, heights, and anything else the property owner wants to know. That data is extrapolated to the entire area to provide an estimate of tree volumes, and thus the value, in much the same way that polling gives an estimate of election results.
This is what a typical waypoint file looks like in my Garmin software. When those points are loaded into the GPS unit, I can bring up a display showing the bearing and distance to any of the waypoints. Then I walk in that direction until the distance is close to zero, and I begin measuring trees.
I first began using GPS in 1994, and for the next ten years or so, I used it to make maps, rather than to follow them.
To make a map, you need a GPS unit capable of storing location data, and software that will turn that information into something more useful. Twenty years ago, that might have involved spending several thousand dollars; today, with advances in technology, it’s cheaper, easier, and better. I won’t even go into all the products and apps that are available, because I’m not very familiar with them. I use what works for me, and don’t spend a lot of time exploring things I probably won’t ever use.
Even when I am working on a piece of land that has been surveyed, and its area is known to the fraction of an acre, I need to make a map. What I’m looking for is the net forested acreage, subtracting out the fields, ponds, power lines, stream buffers – any areas that have no trees, or have trees that will not be cut. Usually I begin with a digital aerial image that is available from a public source. The image has been georeferenced, meaning that each pixel corresponds to a given latitude and longitude on the face of the earth.
Here is a timber sale I worked on in 2011. The land is privately owned by an individual who actively manages for timber production. Location is in central Georgia. It is common to grow trees on a rotation of 25 to 35 years, clearcut, and start over. It’s not my intention to get into a drawn-out battle about clearcutting; that can be another diary, or series of diaries. From the image posted above, it’s obvious that there are lots of trees. A highway is visible on the left side of the map, and a lake on the right. The trees in parallel lines at the top of the image (north) are planted pines that have been thinned.
If I do not have any GPS coordinates to guide me to a starting point, I use road junctions and other landmarks to navigate my way there. In this instance, I was driving in from the north, and I knew that I was to begin at the southern edge of the planted pines. The southern extent of my work was an area that had been cut two years previously (but does not show in this image because it predates that harvest). In the “good old days” before GPS, that’s how foresters and other resource professionals found their way. If you couldn’t interpret an aerial photo, you usually ended up with a desk job where you’d be less dangerous to yourself.
When I arrive in the field, I have a printed copy of the aerial image. I might also have survey plats, or a map from the county tax assessor’s website showing ownership boundaries. The property owner has told me which area is to be cut. Sometimes the boundaries have been marked. If not, then I mark them as I go.
The GPS information that I gather is usually a series of points that can be converted into lines (for boundaries or distance) or polygons (to know acreage). At every change in direction, I take a waypoint. A timber sale might contain hundreds of waypoints, especially when there are streams that require buffers for water quality purposes. As I'm gathering waypoints, my screen looks like this:
When I get home, I add my GPS data to the original aerial image.
The mapping software tells me how many acres are in each polygon, allowing me to know how much land will be clearcut and how much is in stream buffers. Net acreage is very important, because my tree data is expressed in tons of wood per acre. Multiply that by net acres, and you have the estimated total volume. Get the acreage wrong, and everything else is wrong, too.
Seldom do I get to see the result of my work, and have the opportunity to compare my GPS with reality. A few weeks ago, the same property owner wanted to set up a timber sale about a mile farther west than the 2011 sale. I downloaded the 2013 aerial imagery, which showed the area after it had been cut and replanted. Here is my 2011 GPS data, matched with the 2013 image. The match isn’t perfect, but it is very close. I was using a handheld GPS unit that had cost about $400. Each data point had a potential error of 10-20 feet, depending on satellite reception at the moment.
Now you have a better idea of how I employ that amazing technology known as GPS. Like so many new innovations that enter our lives, we come to take them for granted. If all the GPS satellites failed, I’d still get by. But it wouldn’t be nearly as easy.
**
"Spotlight on Green News & Views" will be posted every Saturday at 1:00 pm Pacific Time and every Wednesday at 3:30 Pacific Time on the Daily Kos front page. Be sure to recommend and comment in the diary.
**
Now it's your turn. Tell us what's happening in your corner of the universe.