Atmospheric studies with the Tri-Band Beacon instrument on the COSMIC constellation

Radio frequency transmissions from each satellite in the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) can be used to study the plasma in the upper atmosphere by (1) providing profiles and two dimensional images of the ionosphere and (2) monitoring phase and amplitude scintillations induced in radio waves propagating through the ionosphere. In addition, the received radio data can be applied to the neutral atmosphere by (a) detecting horizontal fluctuations in tropospheric water vapor and (b) yielding accurate position data for satellite drag and neutral density determination. A three-frequency radio beacon called the Tri-Band Beacon (TBB) is being developed for the COSMIC program to provide transmissions at VHF, UHF and L-band. Tomographic imaging of the ionosphere is a recently developed technique that uses integrated measurements and computer reconstructions to determine electron densities. The integral of electron density along vertical or oblique paths is obtained by employing radio transmissions from low-earth-orbiting (LEO) COSMIC satellite transmitters to a chain of receivers on the earth's surface. Analyzing the total electron content (TEC) data using computerized ionospheric tomography (CIT) produces two-dimensional maps of the ionospheric plasma. Difficulties associated with CIT arise from the non-uniqueness of the reconstructions owing to limited angle measurements or non-optimal receiver. Improvements in both reconstruction algorithms and CIT measurement systems are being implemented for the COSMIC mission by combining the GPS occultation data with the TBB measurements of TEC. Once the ionospheric effects on the radio wave propagation have been determined, the Doppler shifts of the UHF and VHF transmissions can be analyzed to give positioning of the COSMIC satellites: to within a few meters. By measuring the effects of the atmospheric drag on the COSMIC satellites, global data for neutral densities in the upper atmosphere can be obtained. There is an additional phase delay of the VHF/UHF/L-bands from the neutral constituents of the troposphere, This phase delay can be used to provide measurements of integrated water vapor. The spatial distribution of water vapor density may be determined with high precision phase measurements from a linear array of ground receivers observing the L-band transmissions of the COSMIC TBB.