Field Navigation Part Two

Use of a compass and map for field navigation

Introduction:

Last week our group, Andrew Peterson, Amy Bartel and I, used available data and resources to create a navigation map. This map included the Priory and the immediate surrounding area. The Priory is located approximately 5 kilometers south of the University of Wisconsin Eau Claire (UWEC) campus on Priory Road. Directions to the Priory from UWEC are as follows. From the main campus area take Roosevelt Avenue east to State Street, turn right on State Street and follow it south until you come to Lowes Creek Road, turn right on West Lowes Creek Road, you will cross over Interstate 94 then come to Priory Road, turn right on Priory Road and watch for the sign for the Priory on your right. Now that we have a usable map and we are at the location the map covers,; how do we use the map to navigate and what are we navigating to?

Methods:

After arriving at the Priory each group was given a list of coordinates (table 1) to points located in the area surrounding the Priory. At each of these points there was a numbered flag with a related paper punch denoting that flag and location. The flags were arranged to produce three individual navigation courses consisting of six locations each. As a class we had six groups of three people each. With only three courses, three of the groups would navigate the courses beginning to end while the other three groups would navigate the courses from the end to the beginning. Our group was assigned to the first course and would navigate it backwards.

Point #	Latitude	Longitude	UTM Y	UTM X	Altitude
1	44.76487	-91.51319	4957906	617662	313
2	44.76573	-91.51378	4958001	617614	301
3	44.76716	-91.5141	4958159	617585	255
4	44.76939	-91.51164	4958410	617775	260
5	44.76804	-91.51072	4958011	617970	278
6	44.76443	-91.51118	4957860	617822	297

  Table.1. Point number, coordinates and altitude for the six points 

  located on the first course. Two groups navigated this course, one 

  navigated the course in numerical order while the other navigated it 

  in reverse order.

The first step to navigating the course was to locate the points on the map. Our map had a UTM grid in place and we were provided with both Latitude and Longitude and UTM coordinates of the points (figure 1). To place the points we followed our grid with its labeled x-y coordinates and transferred the points from table 1 to the map (figure 2), our grid was set at 20 meter intervals so there was some interpolation to gain the most accurate position on the map. At each of the six points we marked the point with a permanent marker, this helped keep the marks visible during inclement weather, and labeled them.

Fig.1. This is the map we produced for use in this exercise.
The map contains and aerial image of the Priory, 5 meter
topographic lines, the search area we were constrained to
and a UTM grid overlay.

Fig.2. We are using the coordinates from table one to
plot our way-points  on our map of the Priory.

Now that we had our points plotted and we knew what direction we would be navigating in we could figure out our bearings from point to point and the distance between the points (table 2). To do this we used a map compass. The compass we used was my Brunton type 7. This compass allows you to utilize the grid on the map to set the compass to north after which you can simply read the azimuth bearing. OK  it is a bit more involved than that.

Points	Bearing	Distance (meters)
1 to 6	105	165
6 to 5	47	210
5 to 4	334	445
4 to 3	218	310
3 to 2	172	160
2 to 1	153	110

 Table.2. These are our point pairs and 

  their bearing and distance measures.

To gather the azimuth bearings from the map we begin by placing the long edge of the compass baseplate on the map using it to connect one navigation point to another one pair at a time, in our case we began by connecting point one with point six. We had to be sure the direction of travel arrow always pointed in the direction we wanted to move (figure 3), our point order was 1-6-5-4-3-2-1. Failure to do this could result in traveling the opposite direction we wanted. After lining up two of the points we turn our attention to the housing of the compass. The housing contains the actual needle and a series of parallel lines (orientating lines) in the bottom of the housing. In the North side of the compass housing there are also marks used to adjust for magnetic declination. In the Eau Claire area we have already determined the declination to be approximately 58 minutes west which is minimal enough that for the scale of this exercise we did not worry about it. We turned the housing until the orientating lines ran parallel to the north/south UTM lines on the map (figure 3). This was also critical; the orientation lines are bi-color black and red, red faces north and black faces south. The housing must have the red portion of the lines and the north arrow facing north on the map failure to do this could again lead to navigating in the wrong direction. After we lined up the edge of the compass between two points on the map and adjusted the housing to point north we were able to read our azimuth bearing. The numbers that run around the dial are azimuth. Located under the dial at the direction of travel arrow is an index mark, the number immediately over this mark is the azimuth for our direction of travel from point to point (figure 4). We repeated this process for each of the pairs of points on the map. Two of the sets of points were longer than the compass so we used straight edge from point to point and held the edge of the compass along it. To get the distances between each of the points we used the scale on the map and measured the distance from point to point.

Fig.3. This is a simulation of the UTM grid on our map. This was
done to clearly show how the orientation lines match the north/south
grid lines, the red portion of the lines and the north arrow are directed
north in concert with the map. Also note the orientation of the compass
in the direction of travel from point 1 to point 2. 

Fig.4. Here we can see the index mark beneath the dial of the
compass. The index mark is concurrent with the bearing arrow
on the base of the compass.  The sample bearing here is 148 degrees. 

For the field navigation we use the azimuth bearing we previously determined and the point to point distance. The three members of our group volunteered to each do a job navigating, the jobs were using the compass to determine our bearing (Stacy), pace the distance from point to point (Andrew)and to assist in determining the direction of travel (Amy). This worked well because we each had strong points. Andrew and Amy’s pace counts were very specific and did not very over several trials, and I had previous experience using a compass to navigate. To navigate from point to point we began using the compass to determine the direction of travel. I stood at point one and rotated the housing of the compass until our bearing for the pair of points was at the index mark on the compass housing. Then, holding the compass out in front of me with the direction of travel arrow pointed away from me, turned my body and the compass as one until the red portion of the arrow (north) was within the orienting arrow, also red, inside the housing. An easy way to remember this is “red Fred in the shed”. Once we achieved this we can look across the compass in our direction of travel. Just as when we were using the compass on the map we had to be sure the compass pointed in the direction of travel and that the red portion and north faced north or we would not be navigating in the correct direction. After we got our bearing Amy would walk out in that direction as far as she was able to while maintain a clear line of site with me (figure 5). When she got as far as she could go I would communicate with her verbally if she was close enough or using hand signals to get her as precisely in line as we were able. Then using the distance measured on the map and dividing it by 100 meters then multiplying it by Andrews pace count we could determine the approximate number of paces to the next point. Andrew would pace to Amy (figure 6) and we would repeat this process until we were at or in the vicinity of the point we were looking for. After reaching each of the points we would use the available punch to mark our card, evidence that we found the point (figure 7). Then we would continue on to the next point.

Fig.5. Amy is getting set on our bearing. At this particular spot
the large White Pine was directly in our path. In order to get
around it I had Amy go to the far side and hold her arms out so
I could estimate better where her body center was for our reset.
Andrew is aiding in communication. 

Fig.6. Andrew is pacing to Amy, the process of extending our
bearing and pacing our distance was performed until we reached
our next point.

Fig.7. Amy is using the punch at point two to mark our card.

Discussion:

We encountered several issues while plotting the points. The first was our grid, as instructed we used a universal transverse mercator (UTM) grid on the map. UTM will work with a global positioning system (GPS) system but not so well with a map and compass. Because we were using a compass and magnetic north we should have used a Geographic Coordinate System instead. However, this was not a large issue do the large scale of our map and the relatively short distances we were covering. The second issue was with our choice of marker used to mark the points on the map. We used a basic marker with a wide tip which does not allow for a very precise point, a Sharpie marker would work much better. When gathering the distance and azimuth data for the points we had to give it our best guess as to the actual point on the map. This may have influenced our readings slightly. We also had to account for the fact that when we tested for our pace count we were on flat level and clean ground, during the navigation exercise we were in knee deep snow traveling up and down steep hills. Much of the difference was accounted for by adding paces to the distance, not very precise though.

We were able to successfully navigate from point one to point six a distance of 165 meters. We were off by about 20 feet at point six. From point six to point five a distance of 210 meters, we were right on and had no issues. From point five to point four a distance of 445 meters we were not successful. This stretch contained areas with a very high density of brush and trees which in concert with the large hills caused us to make repeated calculations at short distances. Each time we had to reset we open the door for greater error in our navigation. This combined with the possible errors discussed earlier caused us to miss our target by about 35-40 meters. The time involved in the numerous resetting also limited us to only finding the three points. We were unable to finish the course as we were rapidly losing daylight.  

Conclusion:

This was a great exercise utilizing a very low tech tool, the compass, to do fairly accurate field navigation. Personally, I have used similar techniques to triangulate the position of radio collared animals. By using a radio antenna to get the direction of an animal from your position on a road and reversing the procedure described above  you transfer the bearings from your position to the animal onto a map. you would do this from at least three different points. Where the bearing lines cross each other is the approximate location of the animal. I enjoyed reinforcing those skills and techniques while getting to rummage around in the outdoors.