RS investigators remotely control equipment in the DSN to capture and record data on the attenuation, scintillation, refraction, rotation, Doppler shifts, and other direct modifications of a spacecraft's radio signal as it is affected by the atmosphere of a planet, the sun, moons, or by structures such as planetary rings or gravitational fields. Rather than lock onto one discrete frequency, the open-loop equipment can observe a range of frequencies. The JPL Radio Science System Group has an informative website . Very Long Baseline Interferometry System, VLBI VLBI can be applied to a number of investigations. Two or more widely separated DSN stations observe the same spacecraft or quasar at the same time, using open-loop receivers, and record their data.
Further analysis can precisely determine the relative position of the antennas.
This investigation is called geodesy . With the antenna positions known precisely, VLBI can precisely determine the position of a spacecraft. VLBI can also produce synthetic aperture results such as images of astronomical objects. The GCF uses land lines, submarine cable, terrestrial microwave, and communications satellites. That's a DSS pictured near the top of this page.