Geophysical Applications of Long-Baseline Radio Interferometry

Abstract

Effective wide-bandwidth techniques for making precision phase-delay measurements (errors ≲ 0.1 nsec) over intercontinental baselines are under development by an MIT and Lincoln Laboratory group. The point sources of radio radiation for such interferometric measurements can be either natural (e.g., quasars) or artificial (e.g., beacons placed in synchronous orbit or on the Moon). Possible applications of this technique include: precision determination of global geodetic ties; measurements of tidal oscillations, crustal-block motions (including continental drift), and Earth polar motion and rotation; refinement of values for the precession and nutation constants and for the rate of change of the obliquity of the ecliptic (the latter when combined with ‘times-of-arrival’ observations of pulsars); measurements of the shape of the sea surface; determination of the geopotential and its time dependence; and global time synchronization at the subnanosecond error level. In this paper we describe the basic technique, the limitations on accuracy, useful antenna systems and sources of radiation, geophysical applications, and briefly, the recent experiments performed by the MIT and Lincoln Laboratory group.