Field Navigation: Distance and Azimuth

Introduction:

The purpose of this week’s activity was to learn how to navigate in the field using traditional methods—distance and azimuth. Azimuth is the angle between magnetic North and a point on the Earth's surface. Using the maps we made last week, a compass, and the coordinates of certain points, we were able to find these specific points in the field. We were given a laminated card to punch at each point so as to prove that we navigated to all of the correct points. The field for this activity was a hilly, wooded, one hundred acre plot known as the Priory in Eau Claire (Figure 1).  Though we ran into several road bumps along the way, my group was able to find these points relatively easily.

Figure 1: This is an aerial photo of the Priory in which we were to find our points.

Methods:

Before we were able to go out into the field, we had to plot our points and learn how to use the compass to find azimuth. We were given six points in a course with their X and Y coordinates (in a UTM coordinate system) to plot on the maps we selected from last week. Unfortunately, the maps we chose to use either did not include a grid system, or the grid system was in the wrong coordinate system. My map was the one that was in the incorrect coordinate system. Though I could swear I had the grid in UTM, it clearly was not, and couldn’t be used for navigation (Figure 2 and Figure 3). We were forced to use an extra map our professor had printed out (which was lucky that he had done so) instead (Figure 4).

Figure 2: This is a portion of my elevation map used for the field navigation. As can be seen with the labels on this grid, the coordinate system is not in UTM like Figure 2. The coordinate system here is unknown.

Figure 3: This is a portion of my elevation navigation map for the Priory that is in the correct coordinate system--UTM. The labels here are correct and can be compared to those in Figure 1.

Figure 4: This is the map we ended up using to do our mapping. It was created by another student and is in the correct coordinate system.

Once we had a suitable map, plotting the points was fairly simple. Our points were on the second course of three created by our professor. Since we had six groups of three people in our class, two groups were assigned to each course. For each course, one group would navigate the points in numerical order, while the second group would go in reverse order. We walked the points in numerical order. Once we knew which points we were assigned and which direction we would be navigating them, we were able to match the UTM coordinates given to us by our professor to the X and Y coordinates on the map (Figure 5). The grid on this map was fifty meters by fifty meters, so we had to do some estimating for the location of the points, but we were fairly confident that the points were in the correct location. Each group member located the points individually and then compared them to the others in order to ensure that the points we plotted were as accurate as possible.

Figure 5: This is a table of the relevant information for each of our navigation points in the Priory. The last point does not have distance or pace information because these were not necessary to find our way back to the main building on the plot.

Next, we learned how to use the compass. The steps to finding the azimuth from one point to the next on our map go as follows:

1. Draw lines from one point to the next on our map. This makes it easier when it comes time to measure the angle and distance.
2. Line up North on the compass with the top of our map. The grid lines we had on the map were not perfectly straight and couldn’t be used as a reference.
3. Line up the black arrow on the compass with the line drawn from point to point (Step 1).
4. Find the correlating angle. If the black arrow is lined up correctly with the line from point to point, and the North on the compass is pointing towards the top of the map, there should be an angle number indicated by a small white line on the compass that is the azimuth from one point to the next.

Figure 6: This is a picture of the compass we used to do our navigation in the Priory. 

http://www.target-master.nl/images/Silva%20Polaris%20177.JPG

We repeated this process between each of the six points, working from one point to the next in the direction we would be walking, and then from our last point back to home base. We double checked our angles for each point to ensure accuracy as well. Because our magnetic declination (the angle between magnetic north and geographic north from a certain point on Earth) in Eau Claire is practically zero, we did not have to adjust our compasses for this.

The next step was to determine the approximate distance from one point to the next. We used the scale bar included with the map to make tick marks on a blank piece of paper with labels indicating the distance they represented. Then we lined up the marks on the paper with the lines we drew between points to find the distance. We weren’t overly concerned with the accuracy on this, because we knew that if we were following the correct azimuth, we would eventually find the next point. It was just nice to know about how long we would be traveling between points. The distances ranged from about seventy meters to two hundred and seventy-five meters (Figure 5).

We then determined the role of each member. One member would need to use the compass to find the azimuth and direct the other two members (reference Figure 6). This also required several steps to follow:

1. Line up North as labeled on the compass turntable with the black heading arrow.
2.  Hold the compass flat and away from your body or any metal objects as they can throw off the compass needle.
3.  Keep “red in the shed”. This means that the red part of the compass needle should be within the red North arrow on the compass turntable.
4. Find the correct azimuth for the points you are navigating between and direct other members in that direction.

Another member would “scout” ahead in the direction indicated by the member with the compass to a landmark and line up perfectly with the azimuth. Then, the third member would use their pace count and walk towards the second member in a straight line. The pace count was used to approximate our distance in the field. A pace count is the number of steps taken over a specified distance which is usually one hundred meters. We found our pace counts last week outside of the science building. The team member that had the most consistent pace count out of three trials was selected to use their pace count in the field. Kory had the most consistent count--around sixty-five steps per one hundred meters.

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Finally, we were ready to head out into the field. Our professor led us to our first point—a dumpster in the parking lot outside of the main building on the Priory property. From there we went out into the woods to find our points. This went pretty smoothly. Our distances and azimuth values were accurate and we could usually see the points from about twenty meters away. The points were marked with blaze orange flags which stood out very clearly against the snow on the ground. We then punched our laminated sheet to prove that we navigated to our points. Each point had a unique punch so it was clear whether or not we went to the correct points. We followed the same procedure for all points.

Discussion:

As stated previously, our navigation went pretty smoothly once we were out in the field. The most difficult part of being in the field was simply fighting against the snow. We had the great fortune of being out in the field in the beginning of a snow storm (though it truly wasn’t too bad). The area we were navigating was very hilly with a lot of brush and snow cover, so we had to be careful not to slide down any hills or step in any holes. I also whacked my head against quite a few branches along the way and snapped a few branches into the person behind me. We had to look out for bears that are notorious for living in this area as I informed my team member from Milwaukee as well.

The nature of the field posed a bit of a problem for the pace counter, as well. The count was not entirely accurate because the pace counter had to walk over uneven terrain and work around trees. Luckily, we still had fairly accurate counts and didn’t have trouble finding our points. Another problem we had to work around was a large, fenced-off pond of sewage that was in the path between two of our points. Our team did not like the idea of walking all the way around the pond, so we opted for hopping the fence and walking adjacent to the pond, though we had to adjust the pace count slightly. We did this by only counting the steps taken in the direction of the next point, and not those taken perpendicular to the path.

The greatest challenge we had to face, however, was working around the fact that our maps were pretty much useless because they were in the incorrect coordinate system or didn’t have a grid. We would not have been able to find any of our points if there weren’t extra maps to be used. This underlines the importance of ensuring that data is in the correct projection and coordinate system—something that is so easy to overlook while working in ArcMap due to on-the-fly projection. After the navigation was over, I corrected my maps and made sure the grid was in the right coordinate system (Figure 7).

Figure 7: This is the elevation map that I created for the Priory with the correct coordinate system for the grid.

Other than this error, however, I would not change our selected maps. They were clear yet informative. We ended up bringing our maps out into the field for reference along with the map with the plotted points, and they proved to be somewhat helpful. Having the contour lines was perhaps the most useful in finding our location. We could compare areas on the map where the contour lines were bunched together to the steep hills we were walking over. The aerial image was also valuable—in one instance we were able to find our location using landmarks like the freeway and tree line on the map.

Conclusion:

Navigating a field using simple methods is extremely useful for a geographer. As stated in previous activities, one can never fully rely on technology, and a back-up plan should always be lined up in case of any difficulties. As we learned this week, distance and azimuth can be used to navigate a field very accurately. With only a compass and map, my group and I were able to find five different locations over a one hundred acre plot with few complications. The most important lesson I learned from this activity was ensuring that my data is in the correct coordinate system. The activity would have been impossible to complete if we weren’t given an extra map to use because my grid was not in the UTM coordinate system and the points could not have been plotted.