Haystack Geodesy Group

Geodesy and geophysics are concerned mostly with what is going on under our feet, so it may seem ironic that these two disciplines are advanced by looking up at the stars! VLBI techniques, which were originally developed for studying radio objects in the universe can, in effect, be turned upside down to do very precise studies of the Earth.
geodesign Studies

By simultaneously collecting data from a single radio source via a worldwide array of radio telescopes, the relative time-of-arrival of signals from that source to each telescope can be determined to within a few picoseconds (3 picoseconds = 1 mm of light travel time). By observing many radio sources spread widely over the sky over a period of 24 hours, data are collected that allow the ultra-precise measurements of the Earth and its orientation in space. The geodetic VLBI techniques in use at Haystack originated more than three decades ago at the Observatory, which continues to lead the way in new developments and improved accuracy in these important research methods.

Geodetic VLBI in Action -- Among the important applications of geodetic VLBI are:
(*) Measuring tectonic plate motions.
(*) Measuring "post-glacial" rebound.
(*) Measuring and monitoring changes in the Earth’s rotation and the wobble of its axis.
(*) Understanding the interaction between Earth’s mantle and core.

Earth Orientation -- Measuring and monitoring changes in the Earth's rotation and the wobble of its axes.

The planet is perceived to turn at a uniform rate with a steady axis of rotation, but it actually wiggles and wobbles in space and experiences changes in rotation rate every day. While these perturbations are small, they are real and VLBI can measure them. These motions are important in understanding the Earth's dynamics and the physical processes that drive them.

Tectonic Plate Motion -- Measuring tectonic plate motions.

By determining the relative 3-dimensional position of globally distributed telescopes to a precision of a few millimeters, motions of the Earth's tectonic plates can be directly measured. A 10-year time history of the distance between the Westford antenna and an antenna in Germany shows that the separation of North America and Europe is proceeding at a steady rate of about 17 millimeters per year. Global tectonic motions measured by VLBI also allow scientists to measure changes in the position of the famous San Andreas fault in California, where the Pacific plate slips past the North American plate at the rate of about 5 centimeters per year.

Astrometry at Haystack -- Astrometry is the science of mapping the positions of the stars, galaxies, and quasars, and recording the motions of the planet. It may be one of the oldest fields of astronomy and was studied by astronomers such as Galileo, Kepler, and Newton.

We use Astrometry today as an important way to keep time by relating atomic time to the Earth's rotation.