lab01_6.html

GEOG 2043

ENVIRONMENTAL FIELD TECHNIQUES

LAB 6

GLOBAL POSITIONING SYSTEM (GPS) 1

OBJECTIVES

The purpose of this field exercise is to introduce you to the use of the Global Positioning System (GPS). In this lab we will compare measurements made with a relatively inexpensive hand-held unit to a more sophisticated (and much more expensive) TRIMBLE PATHFINDER.

METHODS

The class will split into two groups for the GPS exercise. Each group will be equipped with both types of GPS receivers. Groups will need at least one person to record the data from the GPS units in the field. The data that you record from the GPS units will then be used for post-processing in the lab. Be sure that each of you has all the field data at the end of the exercise.

TASKS

1. Task 1.

Our first task is to demonstrate how the GPS units work. We'll also compare readings from the two units. Go to the Norlin Quad. Select a site that maximizes the satellite view angle. Start both GPS units. Observe how coordinates change with time. After approximately 3 minutes, for each unit record the following:

name your location (e.g. "quad")
x, y, and z coordinates
DOP/HDOP's
number of locked satellites (SV's).
short site description.

2. Task 2.

Here we test the navigational ability of the Garmin GPS unit. A "waypoint" entitled "BUFF PT", has been placed in the Garmin receivers.

Go to the main menu and select Way Point.
Toggle through choices and select "BUFF PT".
Select GOTO key on the HOT KEY pad.
Toggle through the screen selections by pressing the hot key pad "page".
Find a page that you like and proceed to the point. (Hint: think Basketball)".
After reaching the GOTO location,record the same coordinates as in Task 1 (x, y, z, DOP/HDOP's, SV's).

3. Task 3.

Proceed to a geodetic control point by following Dave. Here we are going to see if the accuracy improves with theamount of time we sit at a point. Using both receivers:

Record coordinates when you first arrive (same as Task 1).
Record coordinates after 2 minutes, 30 seconds.
Record coordinates after 5 minutes.
Note that the true position of this point is

Latitude: 40'00'17.99250(N)
Longitude: 105'15'33.97380(W)
Elevation: 1638.80 meters

4. Task 4.

Here we investigate how imporant the satellite view angle may be to obtaining good GPS readings. Proceed NW past the NE entrance to the Coors Event Center,down the concrete walk. Stop in an area with a poor satellite view angle(e.g. you can't see much of the sky). Again, record the same coordinates as in Task 1,using both receivers.

5. Task 5.

Another accuracy test.

On the GARMIN receiver, select the way point "BRIDGE".
Proceed to the way point "BRIDGE" (hint: pond)
Record the coordinates of the "BRIDGE" way point with both receivers when you arrive at the way point. Note your position with respect to the center of the actual bridge.
If not on the center of the real bridge, proceed to the center of the bridge and record the coordinates at that point with both receivers.

6. Task 6.

Again, we investigate how imporant the satellite view angle may be to obtaininggood GPS readings.

Move to a location under a nearby and large tree.
Wait for 3 minutes.
Record coordinates as in Task 1 with both receivers.
You're done; return to Guggenheim.

QUESTIONS

1. For tasks 1,3,4,5,6 (4 points):

o calculate the difference in location using the two receivers, for:

§ latitude;

§ longitude;

§ altitude;

o calculate the difference in location using the two receivers, in meters (hint: 1 second of latitude = 30.843m; 1 second of longitude = 23.721).

o for each task, include a description of the point and the other coordinate information (DOP/HDOP values; SV's). A table may help here.

2. Discuss how well the GARMIN GPS units lead you to the waypoint. What, if any, difficulties did you encounter? 1-2 paragraphs. (1 point).

3. Compare the coordinates from the two receivers to the coordinates from the known geodetic control point. Use a table. Discuss possible sources of error. 1-2 paragraphs total. (2 points).

4. Describe how the DOP/HDOP values varied for the two receivers at each of the recording locations. What do you attribute this to. What affect does the DOP/HDOP value appear to have on the error estimate? 1-2 paragraphs. (2 points).