In general, the ITRFs provided within the last 20 years are based on the combination of the geometric space geodetic techniques: Doppler Orbitography
and Radio-positioning Integrated by Satellite (DORIS), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI); see e.g., Altamimi et al.
on a patient with an intraorbital tumor and demonstrated injected radiopaque dye within the intracranial subdural space .
France has recently embarked on a permanent space surveillance capability in a newly-opened facility near Lyons; manned 24/7 by air force crews, it will deploy the Systeme d'Information Spatiale, a space situational awareness C2 granted to a consortium led by Thales Alenia Space end-2014; the SIS will leverage expert tracking of space weather, as well as the modernised Graves bistatic radar mapping objects in low orbit, designating some to dedicated orbitography
radars or optical telescopes.
and Radio-positioning Integrated by Satellite (DORIS) on board enables precise determination of the orbit.
It will include two (or three) installations that will compute orbitography
, check the integrity of signals, develop radio navigation messages and monitor the services.
DORIS (Doppler Orbitography
by Radiopositioning Integrated on Satellite) technology determines orbits of host satellites (Spot2, Spot3, Spot4, TOPEX/Poseidon and Spot5 in the future), station coordinates and EOP from dual-frequency Doppler observations; the transmitter--see Fig.
The ITRFyy is a practical realization of the International Terrestrial Reference System (ITRS), based on four space geodetic techniques: Very Long Baseline Interferometry (VLBI), Satellite and Lunar Laser Ranging (SLR and LLR), Global Navigation Satellite Systems (GNSS) and Doppler Orbitography
and Radio positioning Integrated by Satellite (DORIS).
Another way to measure distances to satellites is with DORIS (Doppler Orbitography
and Radiopositioning Integrated by Satellite), which was built and is operated by the French space agency, known as CNES.