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.
EO Data Access
