GLONASS – is it worth it?

GLONASS – is it worth it?

Having a GLONASS-enabled SmartRover has major benefits to an RTK solution. Although 5 GPS satellites are needed to initialise the RTK fix, thereafter GLONASS

satellites help to ‘retain’ said initialisation, under a canopy of site obstructions and reduced visibility. In order to determine a position in GPS-only mode the receiver must track a minimum of four satellites (5 for an RTK solution), representing the four unknowns of 3-D position and time. In a combined GPS/GLONASS mode, the receiver must track five GPS satellites and at least 2 GLONASS satellite representing the same four previous unknowns, to determine the GPS/GLONASS time offset.

• GLONASS now numbers 26 Space Vehicle’s (4 in maintenance) as of January 2011. Therefore there is a major increase in the number of satellites that are visible.
• With an extra constellation comes more reliable & robust solutions; GPS and GLONASS can increase performance and accuracy by up to 30% relative to GPS only (Leica Geosystems 2010).
• As GLONASS is inclined at 64.8°, the DOP values are greatly reduced for higher latitudes i.e. the UK
• SmartNet sees significant benefits above 50^oN (UK)
• GPS only: DOP=1.85, GPS+GLO: DOP=1.35
• PDOP % improvement of using dual-constellation is ~25% for the UK
• GLONASS has a different repeat cycle of SV orbits, which importantly changes their sensitivity to multipath (whereas GPS only multipath repeats -4mins/day or every sidereal day)

“The systematic translation of GPS satellite-related errors (as a result of having the same ground-track) doesn’t happen for GLONASS.