A Novel Method for Characterizing Atmospheric Turbulence Using Global Positioning System (GPS)

Smithsonian Institution Astrophysical Observatory, Cambridge MA

Investigators

Abstract

Signals from Global Positioning System (GPS) satellites propagate through the atmosphere with a velocity determined by the refractivity of the air, which depends on temperature, pressure, and humidity. This award supports research based on the principle that the difference between the propagation delays from two GPS satellites measured at the same position on the ground depends on the difference in the integrated refractivity along the two ray paths. The propagation delays are calculated from the measured phases of the GPS signals and are subject to uncertainty because of clock errors, uncertainties in satellite range, and receiver noise. However, short-term fluctuations of the phase difference about averages over periods from a few seconds to minutes are largely free of these uncertainties and depend mainly on changes in the path-average refractivity. These fluctuations are caused by the variability of atmospheric structure and hence may be regarded as a measure of the irregularity, or turbulence. The objective of the work is to evaluate the feasibility of continuous, accurate, all-weather remote sensing of turbulence by monitoring GPS signals. It holds the potential of improving weather forecasts and alleviating aviation hazards through better understanding of the occurrence and distribution of turbulence.