Angular Position Determination of Satellites Using Vlbi and Δ-Dor Methodology

The name, Differential One-way Ranging (Δ-DOR), comes from the fact that only a range difference, rather than an absolute range, is determined and that only the downlink is used. For a spacecraft, the one-way range is determined for a single station by extracting the phases of two or more signals emitted by the spacecraft. The DOR tones are generated by modulating a sine wave or square onto the downlink carrier at S-band, X-band, or Ka band. DOR observables are formed by subtracting the one-way range measurements generated at the two stations. The station differencing eliminates the effect of the spacecraft clock offset, but DOR measurements are biased by ground station clock offsets, instrumental delays and media effects.