Using a GPS Receiver to find a site location.

When you are establishing a field site for any GLOBE protocol, one of the first measurements that the students must make is to determine the location of the site. The Global Positioning Satellites (GPS) provide a relatively quick and accurate location which can be improved in accuracy by averaging the readings taken every minute for five or more minutes. This improved speed of measurement is due to the recent (May 2000) deactivation of some of the GPS Satellite imformation dithering features. Thus only about five minutes of data need to be recorded (at one minute intervals).

Turn on the GPS receiver and let it acquire sufficient satellite data to display position coordinates. Insure that the receiver is in the open, (out of doors) has a charged battery, and is held still near or on the surface to be measured. In most cases, the degrees of latitude and longitude will remain the same throughout the process, but the tenths and hundredths of a minute readings will fluctuate similar to the displays illustrated below. Record the readings on the display for later analysis. For clarity, each of the readings have been entered as text to the right of each photograph.

Practical Exercise 1

Given a handheld GPS receiver with the following screen photographs taken at one minute intervals,

Calculate the coordinates and altitude for the site to the nearest 0.01' (minute) of latitude and longitude and meter of elevation.

8 Sep 99 @ 00:01:00 UT

N 36°13.190'

W 092°19.045'

440 feet above MSL

8 Sep 99 @ 00:02:00 UT

N 36°13.190'

W 092°19.038'

427 feet above MSL

8 Sep 99 @ 00:03:00 UT

N 36°13.197'

W 092°19.032'

393 feet above MSL

8 Sep 99 @ 00:04:00 UT

N 36°13.208'

W 092°19.031'

375 feet above MSL

8 Sep 99 @ 00:05:00 UT

N 36°13.218

W 092°19.033'

410 feet above MSL

Enter the values illustrated above on the GPS Worksheet or an Excel Spreadsheet and calculate the averages.