Advanced Data Analysis Techniques for Active Microwave Occultation Experiments

University Of Arizona, Tucson AZ

Investigators

Abstract

This grant advances methods of atmospheric sounding based on measurement and interpretation of GPS signals received by low earth orbiting (LEO) satellites. Because of refraction, radio signals follow a slightly bent path and have a slightly reduced speed when they propagate through the earth's atmosphere from a GPS transmitting satellite to a LEO receiver. From the amount of bending and the excess time delay can be inferred the vertical profile of the radio refractivity of the atmosphere. The refractivity is related to the electron density in the ionosphere and to the temperature, pressure, and water vapor content of the neutral atmosphere. Atmospheric sounding using the occultation technique separates the different contributions to the refractive index to determine both the electron density profile in the high atmosphere and the profiles of temperature and humidity in the lower atmosphere. The project is divided into two main parts. The first is concerned with solving certain problems in using the existing system of GPS satellites to monitor profiles of temperature, humidity, and electron density. It includes (1) developing corrections for the effects of the ionosphere on measurements in the lower atmosphere; (2) studying the effects of multipath propagation in the lower troposphere; (3) extending the profiling down to the boundary layer; (4) assimilating radio occultation data into weather forecasting models. The second part of the project is aimed at developing an advanced sounding system in which an array of as many as six LEO satellites will be equipped for both transmitting and receiving signals at frequencies within selected water vapor and ozone absorption bands (so-called crosslink experiments). Measuring the amplitudes and phases of such signals enables the determination of profiles of temperature, water vapor, and ozone from radio occultations. This research lays the groundwork for new methods of atmospheric sounding that will have important application in numerical weather prediction models and, through the detection of long-term trends, in climate studies.