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The instantaneous Earth rotation rate, usually expressed as variation of the length of day (LOD ) and the orientation of the rotational axis of the Earth in space are the quantities which link the terrestrial (ITRF) and the celestial (ICRF) reference frames. Currently a set of very distant quasars, forming an external set of stable reference markers, provide the only way of determining the rotational velocity and the variations of the orientation of the rotational axis of the Earth with sufﬁcient accuracy for precise point positioning and navigation on the Earth’s surface. Typical values of less than 10 s for the measurement of LOD and 0.5 nrad (0.1 mas) for the pole position are routinely achieved by a network of radio telescopes and satellite observations , by the services of the International Association of Geodesy (IAG). The operation of such a network requires extremely expensive equipment and a massive maintenance effort. Huge amounts of data are recorded in each measurement session, which require physical transport over large dis-tances for the correlation process in the analysis centers. Because of issues such as data latency and the fact that there is no continuous measurement coverage, it is highly desir-able to investigate complementary methods for the precise estimation of Earth rotation. Furthermore, the development of independent measurement techniques will allow for the identiﬁcation of intratechnique biases if they exist.

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