WSP01392

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 6/1/2000
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2000
• Water Supply Pro - Doc Type: Publication

the precision to which angles can be measured and distances can be measured. Because

distance can be measured repeatedly and can be averaged, accuracy is generally contingent

upon angle measurement and can be expressed as a function of the measurement distance.

With a horizontal and vertical accuracy of3 arc seconds, the relative horizontal and vertical

error is l.4SE-S of the measurement distance. Because an effort was made to not shoot points

at a distance of more than 1000ft from the total station, the amount of error introduced by the

machine was limited to less than +/- 4mm.

Global Positioning Systems and Sonar

In 1999, a second technique was used to gather bathymetric surveys of the channel.

Global Positioning Systems (GPS) and sonar technology were used together to allow the

mapping of the channel from a moving boat, thereby gathering a large amount of data in a

short amount of time. In recent years there have been advances in GPS technology but the

basic concept ofGPS remains the same. GPS satellites with known orbits broadcast pseudo

random code which is synchronized to universal time. A GPS receiver receives the signal and

calculates a distance to the satellites based on the amount of time required for the signal to

reach the receiver. Using trigonometry, it is possible to locate a single point in space if you

know the distance to four other known points.

The GPS satellites have atomic clocks on board which allow them to all broadcast

pseudo random code in complete synchronicity. Because the receiver does not have an atomic

clock on board from which to determine universal time, it looks for a single time correction

that will allow the receiver to resolve the four time signals to into a single point. Once the

receiver has determined universal time, it can then determine the time offset and distance to

the satellites.

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