| Summary: | The “Radio Occultation (RO)” method is one from the simple, accurate and high resolution methods that produces a complete atmosphere model. Each region/country optimizes a “Low Earth Orbiter (LEO)” satellite orbit that covers its climate requirements by processing the “Global Navigation Satellite System (GNSS)” received signal. Orbit optimization includes the six Keplerian parameters that define the orbit shape. The optimum values of the Keplerian parameters are based up on the number and the distribution of the observations located in the country or the case study region. In the present research, a GNSS-LEO orbit optimization is made for Egypt and the Middle East region. The research objective is to feed the case study region by an adequate and uniform distributed number of observations. Both of time and spatial distributions are taken in consideration in deferent orbits comparison. Two GNSS constellations, “Global Positioning System (GPS)” (29 satellites) and “Global Navigation Satellite System (GLONASS)” (24 satellites), data are used in the analysis. More than hundred orbit cases are used for analysis to find the optimum one.Research demonstrated that the proposed orbit parameters for Egypt area are: altitude = 1500 km, inclination = 0°, initial value of mean anomaly = 300° and the other parameters are set to 0 values. The average expected number of observations due to this orbit is 8 observations per day in Egypt. Results also showed that the proposed orbit parameters for Middle East region are: altitude = 1500 km, inclination = 0°, initial value of mean anomaly = 330° and the other parameters are set to 0 values. The average expected number of observations due to this orbit is 854 observations per day in the Middle East region. These orbits insure obtaining the maximum number of observations with the best spatial and time distribution. The only deference between the two orbits is the angle of the initial value of the mean anomaly. If it is set to 300°, the observations distribution is expected to be distorted over the Middle East region by a small value. And if it is set to 330°, the number of observations through Egypt will be reduced to 7 instead of 8 observations per day. Keywords: GNSS, Radio occultation, LEO, Atmosphere, Climatology
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