Session III GPS DEPTH-FINDER UNITS

2. GPS positions are not error free User and/or Satellite clock bias. Satellite signal can be blocked. Atmospheric interference is possible. Poor satellite geometry is possible.

3. Signal Quality and Accuracy The height of the bars in display shows signal quality from each satellite The number of items show the positions of satellites currently in view to your GPS. Receivers acquire and process data from satellites to estimate the user’s position Some use all available data for optimal positioning--others select and use most suitable combination Because satellites positions vary continually, the receiver switches satellites in use Receivers make additional calculationsReceivers acquire and process data from satellites to estimate the user’s position Some use all available data for optimal positioning--others select and use most suitable combination Because satellites positions vary continually, the receiver switches satellites in use Receivers make additional calculations

4. Horizontal Dilution of Precision Horizontal Dilution of Precision (HDOP) is a measure of satellite fix geometry quality Figure at far left has lower (better) HDOP GPS receivers measure and display HDOP

5. Estimated Position Error“EPE” Many GPS units display EPE It’s an expression of the diameter of a circle in which your position target exists EPE is expressed in feet or meters – user choice

6. Specifications Accuracy GPS without SA - 100 meters GPS with SA - 10 meters(33 ft) 95% of time DGPS – approx 10 feet, 95% of time WAAS – approx 8 feet, 99.85% of time

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