| Summary: | 碩士 === 國立中央大學 === 太空科學研究所 === 92 === During April 1995 to Feb.1997, the University Corporation for Atmospheric Research (UCAR) collected about 230 daily occultations and several tens of thousands of radio occultation profiles of the Earth’s atmosphere and ionosphere properties by making use of GPS/MET system to measure the total electron content (TEC) values. Nowadays the Constellation Observing system for Meteorology、Ionosphere and Climate (COSMIC) program has been organized six low-earth-orbit (LEO) satellites to receive the limb-viewing GPS signals by means of radio occultation(RO) technique and will launch the LEO satellites during the fall of 2005. The mission is expected having more than 3000 occultation observations per day and can retrieve vertical profiles of ionospheric electron density and other atmosphere parameters, e.g. pressure, temperature, and water vapor pressure, etc, through the measurements of total electron content (TEC) and/or bending angles.
The paper applied computerized ionospheric tomography (CIT) technique to reconstruct the images of the distribution of electron densities for studying large scale of horizontal ionosphere. The GPS/MET ionospheric tomography images have been derived by utilizing MART algorithm and then be verified by the “true” images that are reconstructed the simulated TEC values using the IRI model (International Reference Ionosphere model). Before the COSMIC satellites will be launched in 2005, we want to use the satellite kit tool (STK) to simulate the positions of satellites and make use of IRI model to simulate TECs of occultation observations and then derived by the MART algorithm to reconstruct the three dimension ionospheric images. The three-dimension electron density images and the simulations could be used in ROCSAT-3 data. That will be great help for us to research the ionospheric weather、radio communication、and Sun-Earth relation.
In the last, the paper will describe the ITS20 receiver station which will receive OSCAR/NNSS type satellites beacon signals at frequencies 150 and 400 MHz and gain the relative TEC 、ionospheric scintillation. National Central University will establish the new –LITN (new Low-latitude Ionospheric Tomography Network) including three stations with ITS20 receiver over Taiwan area for studying and observing ionosphere in the future.
|
|---|
