Navigation with a Map and a Compass - Week 2

Introduction

In this activity, the navigation maps that were created in the previous week's activity, will now be utilized along with a compass and GPS unit to navigate the selected study area. Primary components used in land navigation include the following:

• Compass
• Topographical map
• Pace count
• Following a bearing
• Adjusting for declination

The link below provides more detail on land navigation:

http://www.backcountryattitude.com/land_navigation.html

Methods

For this exercise, students utilized the following:

• Navigation map in UTM (figure 1)
• Navigation map in decimal degrees (figure 2)
• Trimble Juno GPS (figure 3)
• Compass (which can be seen in figure 4)
• Pink ribbon (for marking trees at designated GPS coordinates)
• Pen
• Ruler

Figure 1: Navigation map (UTM Zone 15N)

Figure 2: Navigation map (decimal degrees)

Figure 3: Trimble Juno Series GPS unit

Figure 4: Measuring and marking bearings on the UTM navigation map

Each group was given a set of GPS coordinate points that were to be navigated to using the maps and compass. The coordinates were in UTM format and were therefore located on the UTM map and marked for the purpose of then finding and marking the bearings from point to point. The points used in this exercise were as follows:

1. 617708, 4958257
2. 617930, 4957946
3. 617619, 4958049
4. 617852, 4958136
5. 617695, 4958123

Each group was to choose a starting point (ours was on the north side of the building) and proceed to each coordinate point in order from 1 to 5. In order to calculate the correct bearings from point to point, a compass was used by lining up the left or right side straight edge of the compass with the starting point and the destination point. Then the compass dial was turned until "red in the shed" was acheived - that is, until the compass north arrow fell within the compass dial outlined arrow (figure 4). The bearing then was the azimuth on the compass dial that lined up with the fixed directional arrow on the compass (the black arrow located on the top center of the compass). 

After the points and bearings were marked on the map, each group member figured out his or her own pace count. The pace count was determined by calculating how many steps one takes within a given distance (100 meters for this exercise). A measuring tape was pulled out to 50 m in the parking lot where students walked alongside the tape while counting their steps. I walked the stretch of tape once and multiplied my result to get a pace count of 116.

After pace counts were determined, Dr. Hupy set up the GPS units to display the coordinates of the current location and to track students' paths through their respective courses. Finally, once the GPS unit was ready, it was time to navigate the course. 

The terrain that students navigated mainly consisted of fairly thick woods with both older, larger trees, and very young, smaller trees (figure 5). The relief was inconsistent where some spots were smooth and flat and others were quite drastic (figure 6). One group member handled the compass and navigation direction while the other two each handled a map and the GPS unit. Using the compass, a landmark was picked in the azimuth, the group walked to it with the compass bearer leading the way, and after the landmark was reached, another landmark was picked. This continued until the point was reached where the GPS unit was used to verify the correct coordinate location.

Figure 5: Section of woods on navigation course

Figure 6: Reaching GPS point 1 in a deep valley

This process continued until the course was complete. Pink ribbon was given to each group to mark a tree at a coordinate location if no tree had already been marked (figure 7). This occurred at point 2, where the GPS confirmed that we were in the correct coordinate location, but we were unable to find any marked trees and so we marked one ourselves. Also, as a way of checking the we were on the correct navigation path, we would stop about halfway between each point and gather our bearings by using the GPS unit to mark our location on the navigation map, then calculating the bearing and continuing onward (figure 8).

Figure 7: Marking a tree at GPS point 2

Figure 8: Using the GPS and map to gather our bearings

Results/Discussion

The result of our GPS tracks can be seen below, where the tracks are the red dots that form a serrated line and the green triangles are the GPS point labelled 1 through 5 (figure 9).

Figure 9: GPS points and tracks of navigation exercise

Looking at the resulting map, it's clear to see that the tracks do not pass directly through each point. In fact, it only passed directly through point 2, came near point 3, and was further away from points 4, 5, and 1, and the tracks show that our path from point to point was not have extremely efficient routes. There was some deviation off of a straight-line path from most points, especially from the starting point to point 1 and point 2 to point 3 after we navigated around the school.

We found that, for most points, our compass bearings were not leading us directly to the points, therefore forcing us to gather our bearings and recalculate the azimuth to the point. This may have been due to the map we were using (UTM), not taking declination into account, or not following the azimuth correctly. By the time the exercise was finished, we found that we did not even utilize our pace counts and thought that it would not have been that useful anyways (even though it may have) due to the hilly and wooded terrain that forced us off a straight line from point to point and to take steps that were not consistently separated as they had been in the parking lot. Since the coordinate points had been given in UTM coordinates, we did not even utilize the map with decimal degrees. Perhaps having used this map to navigate would have led to better results for our tracks. Using the GPS unit was helpful in gathering our bearings and recalculating the azimuth. Without it, we may have not found the points we were looking for. The contour lines featured on the maps was also not something we utilized very well. Perhaps having contour lines in conjunction with a slope feature class of the terrain would have helped us visualize the terrain we were navigating a little better.


Conclusion

While this activity was not a complete success, it was also not a complete failure. While our group had a good plan in place going into the exercise, we found that by the end we could have employed better navigation methods, and it is because of this that we learned a great deal of what it takes to navigate in a remote terrain (or at least got an idea).

Sources

GPS image: http://mountliming.co.uk/precision-farming/gps-hardware-and-software/