Chapter 5 - Understanding Position Coordinates
Page 5-4
961 Operations and Reference Manual Rev. D
ference, all of which affect accuracy. HDOP can range from an
ideal value of slightly less than one up to a poor value of 10 or
more; any value less than two indicates excellent performance.
Using DGPS to determine position
Using DGPS to
increase repeatable
accuracy
For a higher level of repeatable accuracy than basic GPS, you’ll
want to use differential GPS, or DGPS.
The 961XD includes an internal differential receiver, and uses
DGPS whenever signals are available. To use DGPS with a
961X, you must convert your Northstar 961X to a Northstar
961XD by adding an internal differential receiver.
DGPS corrections remove the errors caused by Selective Avail-
ability (SA) and atmospheric variations, and provide an accu-
racy that can exceed that which is obtained by military users
of the GPS system. With good DGPS corrections, your 961
should provide better than four-meter accuracy (repeatable
and absolute) 95 percent of the time, SOG readings accurate to
0.1 knot, and COG measurements accurate to about 0.5
degree. For more information about GPS, see ”Using GPS to
determine position” starting on page 5-2.
NOTE:
When using DGPS as your navigation source, your 961’s position
coordinates may actually exceed the accuracy of some charts.
DGPS-in-use
indicator
The DGPS indicator appears as the word
DGPS
in the upper
left-hand corner of the
CHART
screen. When the 961 displays
this indicator, it means that you’re using DGPS’s higher level
of accuracy for received data. When you require this addi-
tional accuracy, check for the presence of this indicator, since
its absence means DGPS isn’t in use.
DGPS status screen
To display more information about received DGPS corrections,
press the
STAR
key to display the
SERVICE MENU
screen,
then press the
GPS STATUS
key. The 961 displays the
GPS
SATELLITE STATUS
screen, showing the DGPS differential
Содержание 961X
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Страница 58: ...Chapter 2 Introducing the 961 Page 2 16 961 Operations and Reference Manual Rev D ...
Страница 140: ...Chapter 5 Understanding Position Coordinates Page 5 12 961 Operations and Reference Manual Rev D ...
Страница 172: ...Chapter 7 Creating Avoidance Points Page 7 16 961 Operations and Reference Manual Rev D ...
Страница 198: ...Chapter 8 Creating Routes Page 8 26 961 Operations and Reference Manual Rev D ...
Страница 262: ...Chapter 12 Alarms TideTrack and Currents Page 12 16 961 Operations and Reference Manual Rev D ...
Страница 348: ...Chapter 14 Service and Maintenance Functions Page 14 20 961 Operations and Reference Manual Rev D ...
Страница 374: ...Index Page I 12 961 Operations and Reference Manual Rev D ...