GPS

MGN 379 Navigation: use of electronic navigation aids

GPS terminal onboard, showing satellites within area. WAAS or wide area augmentation system shows that accuracy should be within 5-7m.
GPS terminal onboard, showing satellites within area. WAAS or wide area augmentation system shows that accuracy should be within 3-5m.
GPS reads the time/distance of the receiver aerial from the satellite. This creates a 'sphere' of position. When four satellites spheres interconnect without error a position can be established on the earths surface.
GPS reads the time/distance of the receiver aerial from the satellite. This creates a ‘sphere’ of position. When four satellites spheres interconnect without error a position can be established on the earths surface.
Currently being improved there are about 27 satellites in GPS that fly low in a sphere passing over 55o N/S
Currently being improved there are about 27 satellites in GPS that fly low in a sphere passing over 55o N/S
The GPS terminal checks for cocked hat error. If this is found the GPS internal clock error is calculated and applied to all readings until the error is zero.
The GPS terminal checks for cocked hat error. If this is found the GPS internal clock error is calculated and applied to all readings until the error is zero.
Good DOP is obtained when the satellites are above the horizon and away from the local zenith.
Good DOP is obtained when the satellites are above the horizon and away from the local zenith.
Poor DOP (dilution of precision) is where the closest satellites are directly overhead (or too low on the horizon)
Poor DOP (dilution of precision) is where the closest satellites are directly overhead (or too low on the horizon)
GPS has three segments. User segment by ships and vehicle Ground segment by integrity monitoring stations and control Space segment used by satellites
GPS has three segments. User segment by ships and vehicle, ground segment by integrity monitoring stations and control space segment used by satellites
GPS uses WGS84 as a standard reference system. This means that if any paper or raster chart is built around another datum the positions may be inaccurate. 'Positions' box on the chart will tell you if this is the case. Here the red line indicates the actual position of the land in WGS84 compared to the chart.
GPS uses WGS84 as a standard reference system. This means that if any paper or raster chart is built around another datum the positions may be inaccurate.
‘Positions’ box on the chart will tell you if this is the case. Here the red line indicates the actual position of the land in WGS84 compared to the chart.
Be careful not to put a navigation mark in as a GPS co-ordinate. Sometimes GPS is all too accurate!
Be careful not to put a navigation mark in as a GPS co-ordinate. Sometimes GPS is all too accurate! Now see MIN 453 this shows that where DGPS is not utilised, or a beacon has declared itself unhealthy, ionospheric events and reduced satellite availability may increase standalone GPS horizontal position errors with occasional large spikes in the errors