Satellitaltimetri

Satellitaltimetri is a term used in Italian-language contexts to describe the field focused on measuring, distributing and synchronizing time through satellite signals. It encompasses methods that enable precise time references to be shared over large geographic areas, integrating space-based clocks with ground-based timing systems.

The most common approaches are GNSS time transfer and two-way satellite time and frequency transfer (TWSTFT). GNSS time transfer uses signals broadcast by satellite constellations (such as GPS, Galileo, GLONASS and BeiDou) to compare a local clock with the time reference carried by the satellites, allowing a ground station to discipline its clock to a chosen standard. TWSTFT, by contrast, exchanges timing signals in both directions between two sites via a communications satellite, and cancels round-trip delays to achieve high accuracy in the clock offset and frequency comparison.

Key components include highly stable on-board atomic clocks on satellites and ground-based timing laboratories equipped with precise receivers and measurement equipment. The measurable outputs are clock offsets and frequency differences relative to international time scales. GNSS time transfer can continuously align local times to civilian and international scales such as UTC and TAI, with national metrology institutes providing calibration and steering.

Applications span critical infrastructure and society: telecommunications networks, financial trading systems, power grids, data centers, and scientific experiments that require synchronized timing. Challenges include dependence on satellite visibility, atmospheric disturbances, and security concerns such as jamming and spoofing. The field is overseen by international time standards organizations and national metrology institutes, which maintain and compare time scales to ensure coherence of civil time.