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A simulation analysis to optimize orbits for a tropical GPS radio occultation mission


Space-based Radio Occultation (RO) measurements using a GPS receiver on a low Earth orbiter (LEO) provide accurate atmospheric refractivity profiles. EQUatorial Atmospheric Research Satellite (EQUARS) is a planned satellite mission carrying a GPS receiver for RO measurements, whose main focus is to study the vertical coupling process in the equatorial atmosphere and ionosphere through upward propagating atmospheric waves. This paper presents a model simulation to determine the best practical orbital parameters of a LEO satellite for GPS occultation, which provides dense occultation coverage from 20°S to 20°N and sparser coverage extending to 30°S and 30°N. Constellations of 29 GPS satellites are computed every 10 sec using the six Keplerian parameters based on real almanac data, while various orbits of LEO satellite are computed by varying orbital parameters, especially orbital altitude and inclination. Then, the occultation events are simulated under the assumption that the ray path between the occulting GPS and LEO satellites is a straight line. The simulation analysis shows that altitude and inclination angle of orbit are considered as principal parameters among the Keplerian parameters to accomplish the RO measurements in the equatorial region. Taking into account the long-lived mission, an avoidance of ionospheric F-layer influences, and practical antenna field of view, the best practical orbit for RO measurement in the equatorial region has an altitude of 750 km and an inclination of 20°. LEO on this orbit is expected to provide 530 RO events per day. The analysis also shows that three LEOs in that orbit with 120° separation can provide atmospheric profiles at least once every 6 h within 1000 km from an arbitrary station in the equator.


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Correspondence to Ashraf Mousa.

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Mousa, A., Aoyama, Y. & Tsuda, T. A simulation analysis to optimize orbits for a tropical GPS radio occultation mission. Earth Planet Sp 58, 919–925 (2006).

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Key words

  • GPS
  • Low Earth Orbit (LEO) satellite
  • radio occultation
  • mission simulation