Instrument: Global Positioning System Receiver
The Global Positioning System (GPS) is a U.S. space-based radionavigation system that provides reliable positioning, navigation, and timing services to civilian users on a continuous worldwide basis. The U.S. Air Force develops, maintains, and operates the space and control segments of the NAVSTAR GPS transmitter system. Ships use a variety of receivers (e.g. Trimble and Ashtech) to interpret the GPS signal and determine accurate latitude and longitude.
NorthStar 941 GPS receiver NMEA (National Marine Electronics Association) output
Format:
$--RMC,hhmmss.ss,S,lat,a,lon,a,x.x,y.y,ddmmyy,m.m,d*hh<cr><lf>
Time = UTC of position fix
S = Status ("A" = valid, "V" = receiver warning)
Lat & Lon
x.x = speed over ground (knots)
y.y = Course over ground (degrees true)
ddmmyy = date
m.m,d = magnetic variation, degrees ("E" subtracts from true, "W" adds to true)