Part II: Section B
 
Using GPS Technology
4.2 Field Test

Our test consisted of taking points along the perimeter of a tall fescue field and a ponded area in a wheat field at Sauvie Island, 10 miles northwest of Portland, Oregon. Specific points that defined the edge of the field were globally positioned with both units operating in point mode. Both the line file and the point file from the Trimble unit were post-processed using a community base station at Portland State University.


Reference base station: Differential Correction Base (reference) data was downloaded from the Community Base Station (CBS) at the Portland State University. This CBS is located approximately 150 km from the Oregon State University Campus.
 
Field Data Logging Procedures
 
1.
  All GPS observations were made at approximate antenna height of 1.5 meters for the Trimble unit and 1 meter for the Magellan unit.
       
2.
  Before logging and positions, we had:
  a.   At least 4 satellites in view for the Trimble unit
  b.   WAAS signal for the Magellan unit
       
3.
  A total of 43 locations along the field perimter were acquired using both GPS units.
       
4.
  All GPS data was logged at 1 position per second.
       
5.
  All data was logged using a postion dilution of precision (PDOP) mask of 6 (Trimble unit). The lower the PDOP, the better the accuracy.
       
6.
  All GPS data collected with the Trimble unit was saved into the data logger.
       
7.
  All GPS data collected with the Magellan unit were also saved into the receiver and transferred using the DataSend software.
     
8.
  Minimums of 15 positions were logged for each location.
     
9.
  At each location, logging time was the same for both units
 

Data Processing Procedures

Trimble Unit:
Data were post-processed using the Trimble Pathfinder Office software package. Post-processing consisted of differential corrections of the raw (*.ssf) receiver files using the Portland State University CBS. The corrected (*.cor) files then were exported in database format (*.dbf).

Magellan Unit:
Data from the Magellan unit were converted from degrees to UTM using Global Mapper ® software.

Data Analysis:
The data analysis was conducted using a Microsoft® Office 2000 Excel spreadsheet. Display of the data and area estimation were performed using Arc/View ® 3.3 GIS software.

All data were analyzed using:

Coordinate System: Universal Transverse Mercator (UTM)
Datum: North American Datum of 1983 (NAD 83)
Zone: 10 North
Unit: Meter
 
<< previous page  
1. What is GPS?
2.How Does GPS Work?
3. Instuctions for Using SporTrak GPS Recievers
4. Performance Testing
- 4.1 Equipment
- 4.2 Field Test
- 4.3 Test Results
- 4.4 Conclusions
5. Glossary
 
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