NorthStar 958, Operator'S Manual

Page: 195 / 232

958 Operator’s Manual, Rev. A Page 187
Figure 9: Position accuracy of uncorrected GPS
With good DGPS corrections, your 958 should provide better
than four-meter accuracy (repeatable and absolute) 95 percent
of the time. SOG readings should be accurate to 0.1 knot.
You can connect your 958 to your loran receiver (as long as
the loran has the appropriate NMEA 0183 output capability),
and display and navigate with real-time loran TDs. With this
configuration, you’ll keep the repeatable accuracy of your
loran, but will add all of the navigation features of the 958,
including the worldwide absolute accuracy of GPS.
Introducing radar
The name RADAR is derived from the phrase “Radio detection
and ranging.”
How does radar
work?
Radar is easy to understand if you take this example: Suppose
you shout towards a cliff, and in a few seconds you hear the
echo. Knowing the speed of sound is constant (approximately
1,100 feet per second), you can therefore start a stop-watch at
the time you yell (moment of transmission) and stop the watch
when the echo (reflective sound) is heard. Let’s say that time is
6 seconds. You can now calculate your distance from the cliff
by multiplying the speed of sound per second, times the
number of seconds, divided by 2. (Don’t forget: the total time