GPS Radio Occultation

GPS Radio Occultation

Unique Attractions of
GPS Radio Occultation:

  • Assured long-term stability

  • All-weather operation

  • Global 3-D coverage: 40 km to the surface

  • Vertical resolution: ~100 m in the lower troposphere

  • Independent height, pressure, and temperature data

  • A compact, low-power, low-cost sensor

  • High accuracy: Averaged profiles to
    < 0.1 K

GPS Radio Occultation - Atmospheric Profiling with Global Navigation Satellite Systems (GNSS)

According to Dr. R. A. Anthes et al., 2008, in The COSMIC/FORMOSAT-3 Mission: Early Results published in the Bulletin of the American Meteorological Society (Volume 89, Issue 3):

"The radio occultation (RO) technique, which makes use of radio signals transmitted by the global positioning system (GPS) satellites, has emerged as a powerful and relatively inexpensive approach for sounding the global atmosphere with high precision, accuracy, and vertical resolution in all weather and over both land and ocean. On 15 April 2006, the joint Taiwan - U.S. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3, hereafter COSMIC) mission, a constellation of six microsatellites, was launched into a 512-km orbit. After launch the satellites were gradually deployed to their final orbits at 800 km, a process that took about 17 months. During the early weeks of the deployment, the satellites were spaced closely, offering a unique opportunity to verify the high precision of RO measurements. As of March 2013, COSMIC is still providing about 1500 RO soundings per day to support the research and operational communities. COSMIC RO data are of better quality than those from the previous missions and penetrate much closer to the Earth's surface; 70% - 90% of the soundings reach to within 1 km of the surface on a global basis. The data are having a positive impact on operational global weather forecast models.

With the ability to penetrate deep into the lower troposphere using an advanced open-loop tracking technique, the COSMIC RO instruments can observe the structure of the tropical atmospheric boundary layer. The value of RO for climate monitoring and research is demonstrated by the precise and consistent observations between different instruments, platforms, and missions. COSMIC observations are capable of inter-calibrating microwave measurements from the Advanced Microwave Sounding Unit (AMSU) on different satellites. Finally, unique and useful observations of the ionosphere are being obtained using the RO receiver and two other instruments on the COSMIC satellites, the Tiny Ionosphere Photometer (TIP) and the Tri-Band Beacon."

Radio Occultation (RO) Documents

  1. FORMOSAT-3/COSMIC RO Special Issue (73KB)
    GPS Solutions

  2. NSPO Movie on RO (61MB)
    This animation describes the radio occultation technique and shows how RO works on FORMOSAT-3/COSMIC

  3. RO Webcast Module
    Produced by the COMET program in collaboration with the COSMIC Program Office

  4. RO tutorial
    Produced by UCAR's COMET program

  5. GPS RO illustration
    How radio occultation works