GPS handhelds are great when they work. However, they need a clear view of a large area of the sky to get a "fix". Here at HSU, and in many areas around the world, this is hard to come by either because you are in a canyon, have a lot of tree cover, need higher resolution than a GPS can provide or some combination of these factors. In addition, sometimes you may be able to see the features you want to digitize but can't get to them. In these cases, we need to find other solutions to get spatial data that meets our research needs.
Scenario:
This is a group project and all data collection and analysis can be done as a group. The group can create a single MXD project with the points marked. Then, each student should take it from there to create their own maps and final report.
You'll need to checkout the following equipment from the stock room:
You'll need to get together with your partners and create your own protocol and data sheet for this lab. Your data sheet needs to include columns for the following and anything else you might want to include.
For this lab, we're going to be doing a common exercise, mapping the location and, optionally, the size of trees.
The problem with a GPS is that it needs to see at least 3 satellites to obtain a "fix". When you're in a forest or canyon, you can quickly loose the ability to use your GPS. The accuracy of the GSP will also be a problem if you want to identify objects in relationship to one another such as the objects shading a stream. One method to overcome this is to establish a "station" where your GPS works and then "shoot" the location of what you are interested using a compass and then measure the distance to the location. Then, you can use a little bit of trigonometry to compute the location interest from the known point at the station.
Note: previous classes have found that the GPSes we have are actually pretty good even in tall stands of redwoods. I still feel this exercise is of value in case you have to "shoot" locations that are not accessible and to understand how most of the older data sets were collected.
We'll be heading to the entrance for the Arcata Forest and establishing a benchmark. Then you'll find the location of one tree by shooting the tree with the compass and range finder. Then, you'll move to the tree, take a GPS reading for that tree and shoot the next tree. You'll repeat this process for at least 5 trees. You can also estimate the height of your trees. There are a variety of methods for doing this and you can come up with your own or use the one described by the instructor. The trees should take you into the forest between Park Dr. and Gannon Slough.
I also recommend taking notes and even photos as you do the survey. It is very common to be back in the office with field data and wish that you had taken more notes in the field. I have never heard anyone say they wished they took fewer notes!
Download the data from the GSP as in the previous lab. Create an MS-Excel spreadsheet and add your field data and then columns for:
Note: Streams and roads are dangerous and you must be careful! Use the range finder directly when possible. When using the leveling rod, please be careful and do not attempt capture points that put you in danger. Also, if anyone in your group is limited in their mobility, feel free to stick to measure trees just along the road or a flat path.
You may want to make two shapefiles from your data; one for the GSP coordinates and one for the compass/range finder coordinates. In ArcGIS, create a map that clearly labels the coordinates that were measured with the GPS and those that were measured with the compass/range finder.
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