Marine GPS Receiver

A marine GPS receiver calculates its distance from satellites using the speed of light.

A GPS satellite transmits only a digital code for identification, but not time.

For accurate position fixing with GPS, a receiver must contain an atomic clock.

GPS receivers solve simultaneous equations using pseudoranges to determine latitude, longitude, and clock error.

A minimum of five satellites are needed to determine altitude for recreational marine applications using GPS.

All GPS satellites transmit on different frequencies, with each frequency indicating the satellite's specific identifying information.

GPS satellites orbit at an altitude of approximately 10,900 statute miles.

GPS satellites complete a single orbit around the earth in approximately 24 hours.

Vertical accuracy is more useful to boaters than horizontal accuracy.

Differential GPS signals alert users if a GPS antenna is malfunctioning.

Differential GPS is a valuable component of the 'abandon ship bag'.

External GPS antennas must be mounted high enough to give a clear view all around the vessel's perimeter.

In DGPS, an independent integrity monitor can warn users if a satellite is transmitting an unreliable signal.

A GPS receiver calculates the vessel's position by taking readings from at least two satellites.

GPS is not subject to local interference that can degrade accuracy.

GPS receivers can only display latitude and longitude.

The GPS data display will include the vessel's course and speed over the ground (COG and SOG) continuously computed from successive position computations, "smoothed" over a user-selected interval (typically 5 to 20 seconds) for greater accuracy.

The GPS signals include very precise time information that is displayed as local zone time.

The clocks of GPS satellites, out in space, are synced with the UTC time.

Differential GPS can correct the error arising from how the atmosphere delays GPS signals.

External GPS antennas should be mounted where it will be in the beam of radar pulses.