Use of the Forest

Public use of Saginaw Forest is encouraged. Rules for the public's use include (but are not limited to):

Monday, April 19, 2010

Working on mapping the forest

Today and tomorrow, I'll be out mapping the forest for a better understanding of what projects are being undertaken out in the forest in order to better determine what sorts of things will be able to be done viz the management plan.

There are some problems that I've run up against with regard to using the GPS unit. First of all, the ever-greening forest canopy creates some havoc with the satellite acquisition, thus making the points somewhat problematic. A second one is that the program that Garmin uses can export to Google Earth, but not to the ArcGIS software that I am using for the analysis. This means that I have to do spatial projections and re-projections, and through all of these processes, the end results are not as accurate as I would like them to be. Still, they are better than nothing.

Another problem is that of the sampling rate at which the Garmin unit takes measurements. The unit only samples so many times per minute, which means that if I move through the forest quickly (i.e., run or cycle), then the paths it maps are very point-deficient, and this is exacerbated by the low signal strength caused by the canopy (see above). However, if I move more slowly, I should be able to get a better resolution on the site, but if I move slowly through an area with a dense canopy, the measurements will not be accurate. This means that, while I may have more points (and therefore potentially a higher level of resolution), these points may not be as accurate, meaning that they might not be very useful.

A third problem is that of the spatial projection. The Garmin unit takes latitude and longitude measurements. (It also takes elevation measurements, but these are not very good, since they depend somewhat on air pressure, making the measurements inconsistent, especially at fine scales.) However, the ArcGIS program needs to have the data projected onto a mapping coordinate system. First, though, in order to feed the data into the ArcGIS program, it needs to be in a format that is recognized, and this requires the use of another program (GPS Utility), and this utility uses a particular datum, the projection from which into the Michigan GeoRef coordinate system means that there is some slight shifting that needs to manually be accounted for.

Put all these together (canopy-related signal impedance, spatial resolution, and spatial projection), and the process of translating on-the-ground measurements into a mapping system makes for a slightly annoying process (even if it is a lot more simple than in decades past).

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