Distance Azimuth Survey

Introduction



This weeks survey includes having to create survey plot that is going to be used to identify trees found within the area. This method is used when technology fails, and it is a good backup to use and understand how to use. To utilize this method for survey measurements of azimuth distance and GPS points will be taken.  The distance calculates how far the starting point is away from the tree and the azimuth calculates the distance off of 0 degrees the tree is. 





Study Area and Set Up

The survey area selected for the distance azimuth survey was located on Putnam trail, just east of Philips Hall on the University of Wisconsin - Eau Claire campus.  This area is generally a swamp region during the summer when the water table is at a higher elevation making it difficult to walk through the trees in the shallow spots.  It has a large population of many different species of trees along the trail, which is located at the bottom of the hill which is famous to the students and staff on campus.  This area was selected due to having a large amount of trees to take azimuth directions on. The study area can be seen in a map view located in Figure 1 showing the location of the three study sites.

Figure 1: These are the study areas selected due to the large tree population. In the Green box is study area 1, blue is study are 2, and the red box is study area 3.  North is in the upward direction.  

Once we got to the sites there was some confusion due to not having used any of the equipment before.  The equipment used was measuring wheel, measuring tape which converted into diameter (Figure 2), a compass with the ability to take an azimuth measurement (Figure 3), a laser distance finder that uses ultrasonic, and a distance finder that uses a laser (Figure 3). The class was broken up into three groups to each collect data in the three spots using a normalized method to make it easier to create a spreadsheet once back in the office. The attributes taken for each datapoint included:

1. Longitude (x)
2. Latitude (Y)
3. Distance (meters)
4. Azimuth (degree 
5. Diameter (Breast Height)
6. Tree Species
7. Sample Area Number

Figure 2:  Sarah Ward using the tape measure that converts it into diameter on the fly. 

Figure 3: Jesse Friend and Kyle Roloff (myself) taken a distance measurement (Jesse) and an azimuth reading (Kyle). 

The attributes chosen are each needed to create a survey that uses azimuth data.  To use this data within ArcGIS there needs to be an X,Y point for each tree so the computer can determine based off of the azimuth and the distance where it is located within the survey grid.  Also getting the diameter could determine the age of the tree or another physical feature.  The type of tree could also be used in another application to show what kind of trees mostly populate the Putnam Dr trail.  The last point is just the survey number which helps keep straight which area that point belong too.

Methods

There are many steps that went into this survey which include:

Step one:  Locate the study area.  This was chosen by finding and area that has a large tree population and could easily be identifiable by google maps to make sure the accuracy of the project is close (Figure 1).

Step two: get a gps point of the starting point.  This means that all of the trees survey will be based off of this point therefore it is imperative to get an accurate GPS reading.
Step Three: Pick a tree to start the survey.

Step Four: Use an compass to get an azimuth by directing the compass at the tree.  Where the arrow   on the compass points gives the azimuth (Figure 3).

Step Five: Use a distance finder or the measuring wheel to get a distance from the original point to the tree being surveyed (Figure 3).

Step Six: Use information about trees to figure out what the species is.

Step Seven: Use the measuring tape that converts on the fly into diameter on the tree at breast height (Figure 2).

Step Eight: Record all the information down in a notebook to bring back to the office.

Step Nine: Use the Bearing Distance to Line command found in the data management tools in ArcToolbox. Before being able to use this the data needs to be imported and made into a points feature class.  This is done by creating a feature class and then right clicking on it to select import x,y coordinates.  Then once they are imported as points the next step is to super impose it over a basemap to access for accuracy.  This is important for the final creation so the views can see how accurate the points are.

Step Ten: Use the Bearing Distance to Line Command to create the lines that go in the direction of the trees


Point Eleven: Next use that feature class and use the Feature Vertices to Points tool. Make sure to use the End parameter on this because we do not need the starting point because that is not a tree.

Step Twelve: Create a quality looking map that shows all of the great data collected in the field.











Figure 4: Final Map showing location of Trees from all three survey areas.

Discussion/Results

There were a few problems that stood out right away when looking at the data when imported into ArcGIS.  First off, The x and y coordinates were backwards and luckily that is an easy fix.  The next was that the group with the red study area was having a problem with their gps.  This may have been due to the ridge which was right next to where the initial point was taken.  The solution to this was to move the point closer to the study area even though it may not be exact.  This will be taken into account to determine the accuracy.  If this was for a professional survey it would need to be redone, but should also have been confirmed from another source to make sure it made sense before continuing.  Using this technique can be very useful in some settings when technology fails.  It can be used during any data collection as long as there is one point known, a compass, and a measuring wheel.  It is easy to use as long as the table is set up correctly and and azimuth is set at the correct declination to the area in the world. This can be used to plot trees, plot bomb craters, or plot rock outcrops.  Technology that has replaced this technique includes using distance finders and carrying around a GPS to collect points.  The points can then be Bluetooth transferred over to a tablet that then can have attributes entered in it without having to write down all of the information in a field notebook. The results started off by being off because the points were located a few miles away.  The only way to really fix this was to move it to the correct location using an educated guess.  Next was that the trees and their directions looked really well on the map created.  For group three it looks exactly like the trees this group took.  The results are pleasing except they may not be the most accurate due to being off from the GPS.  Another problem with this is how hard it is to figure out exactly where the study locations were.  It is hard to see through the tree cover making it difficult to distinguish any of the trees.  It would be better to try this survey in an area with less trees to see if the lines actually point to the correct tree.  In my opinion using the newer technology it was very quick to go from point to point.  If using the older technology it was exponentially increase the amount of time spent on each tree to collect datapoints. 




Conclusion



This was a great lab to learn survey techniques that can be used when technology fails.  The only important part is to have a correct GPS point and all the other tools to take distance and azimuth measurements. It is also important to know this because there is no way to predict when technology will fail.  Luckily for us technology made the survey go quicker than having to use the measuring wheel for each tree. The accuracy was about 70% and could have been better if the points were not off due to the ridge.  Also, it can be tedious to do this with the older equipment, but at the end of the day the job needs to be done even if the technology fails.



Photo credits go to Google and Heather Wood.