GLONASS

GLONASS is the Russian Global Navigation Satellite System, the second full constellation after GPS, operated by Roscosmos with a nominal 24 satellites in three orbital planes inclined at 64.8 degrees. It differs from GPS in using frequency-division multiple access on the legacy signals, each satellite transmitting on its own L1 and L2 frequency near 1602 MHz and 1246 MHz, rather than code division. GLONASS uses the PZ-90 datum, transformed to WGS-84 in multi-constellation receivers. Combining GLONASS with GPS raises the number of satellites in view, improving the geometry and lowering GDOP, which helps fixing in steep-sided fjords and among high superstructure.