The Doppler Orbitography and Radio-positioning Integrated by Satellite instrument is a microwave tracking system that can be utilized to determine the precise location of the ENVISAT satellite. Versions of the DORIS instrument are currently flying on the SPOT-2 and Topex-Poseidon missions.
DORIS operates by measuring the Doppler frequency shift of a radio signal transmitted from ground stations and received on-board the satellite. The reference frequency for the measurement is generated by identical ultra-stable oscillators on the ground and on-board the spacecraft.
Currently there are about 50 ground beacons placed around the globe which cover about 75% of the ENVISAT orbit. On board measurements are performed every 7 - 10 seconds. Precise Doppler shift measurements are taken using an S-band frequency of 2.03625 GHz, while a second VHS band signal at 401.25 MHz is used for ionospheric correction of the propagation delay.
On the ground, DORIS data is used to create precise orbit reconstruction models which are then used for all satellite instruments requiring precise orbit position information. In addition, DORIS operates in a Navigator mode in which on-board positioning calculations are performed in real-time and relayed to the ground segment.
Orbit error about 1cm
5 cm in altitude
FOV :130 degrees
Natural Disasters ( Landslide ), Solid Earth ( Tectonics/Seismic Activity )
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