There are two satellite positioning networks which orbit the earth: the Global Positioning System (GPS) and the Global Navigation Satellite System (GLONASS). The GPS network was commissioned in 1993 and the GLONASS in 1996.

The constellations are similar in that both require at least four satellites to be in view at least 10° over the horizon to calculate a fix. Both require at least five satellites to determine if the fix calculated is correct with a 99.9% certainty of its stated accuracy which is the system's integrity. If it finds fault with the integrity of a satellite, it must acquire a sixth satellite to replace the one that failed the integrity test.

The constellations are different in that the GPS accuracy is better than 20 meters for 95% of the time, but this accuracy is denied by a practice called Selected Availability (SA). This has been done for security reasons. This degraded position information is called the Standard Positioning Service (SPS). The stated accuracy is 100 meters for 95% of the time.

The GLONASS accuracy is 8 meters for 95% of the time. The system is not degraded.

Differential Corrections can be applied to either constellation. The accuracy of DGPS is less than 10 meters for 95% of the time. The accuracy of GLONASS is 1 meter for 95% of the time.

Their orbits are different in that the GPS satellites are distributed in 6 orbital planes, 4 satellites per plane at an inclination of 55°. The GLONASS satellites are distributed in 3 planes of 8 satellites each at a 64.8° inclination.

Their satellite almanacs or EPHEMEQIDES, which tell the satellite receivers precisely where each satellite is located, are different. The GPS satellites provide their positions in 'WGS84', World Geodesic System. The GLONASS satellites provide their positions in terms of 'PE90', Parameters of the Earth.

Combining Technologies

The Navigator 24 is a product designed to acquire both constellations simultaneously with its 24 channel receiver which processes 12 parallel channels of GPS and 12 parallel channels of GLONASS to determine position. The results of this approach are dramatic.

Using GPS and GLONASS the position accuracy becomes 7 meters for 95% of the time. Using DGPS and GLONASS the position accuracy becomes 40 centimeters for 95% of the time.

The system automatically selects the most accurate solution based on the signals available and switches from constellation, satellite, and differential signals to always provide the most accurate fix.

Accurate speed over ground, a product in itself, comes with the technology, has an accuracy of .02 knots, is seen in the DGPS and GLONASS mode, and is referenced to angular direction.

Output of Horizontal Position, Vertical Position, and Speed can be sent at 5 times a second to other on board technologies ( i.e., Dynamic Positioning Systems, Bottom Mapping, Ocean Surveying, ECDIS, etc.).

The application in ocean engineering is limited only by our imagination, and this accuracy of position and speed will soon become the new standard for shipboard navigation.