Global Atmospheric Water Vapour Profiling using GPS and GALILEO Satellites

  • Borre, Kai (Projektdeltager)



The project studies the possibilities of monitoring the content of water vapour in the Earth's atmosphere using Global Navigation Satellite Systems (GNSS). Water vapour is the most important greenhouse gas in the climate system of the Earth. It also plays a major role in weather processes due to the large energy transfers related with evaporation and condensation. Dispite of its importance, systems for precise monitoring of the atmospheric water vapour distribution are still missing. The primary focus is on the radio occultation (RO) technique for atmospheric probing. In this method the GNSS signals are tracked by a receiver onboard a satellite in a low-Earth-orbit (LEO). When the GNSS sets or rises behind the Earth limb as seen from the LEO, the signals scans through the shallow atmosphere and are bended and partially absorbed due to the varying refractive index. In previous RO experiments only the bending, which is derived through the measured Doppler shift of the signal, is used to derive vertical profiles of refractivity. Recently, European Space Agency selected the atmosphere and Climate Explorer (ACE+) mission to have first priority in the Earth Explorer Opportunity Mission programme. ACE+ will perform LEO-LEO inter-satellite occultations at frequencies optimized for water vapour retrieval in addition to the GNSS-LEO occultations. We perform simulation studies of the whole measurement concept including wave propagation through the atmosphere and data processing from measured phase and amplitude to vertical profiles of pressure, temperature, and humidity. Another activity in the project is a field test experiment using a state-of-the-art GPS receiver developed by Saab Ericsson Space, Sweden. The receiver is intended for space borne RO mesurements, but in this experiment we place it approximately 4 km above sea level and perform ground-based radio occultations. Preparations and theoretical considerations have been performed while the actual measurement campaign will take place early 2004. The measurements will be done in the tropics where the atmospheric water vapour content is high and convective turbulence is likely to occur, and hence we expect signal scintillations. We will study the receiver capability under these severe conditions and develop methods for using RO data even under scintillation conditions. The project is financed by the Danish Technical Research Council (STVF) and runs for three years. DGC cooperates with Saab Ericsson Space, Sweden in the field test experiment under the project. (Kai Borre)
Effektiv start/slut dato01/01/200431/12/2007


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