Search

The world's first Global Positioning System Radio Occultation (GPS-RO) constellation, the joint Taiwan-U.S. Formosa Satellite No. 3 - Constellation Observing System for Meteorology, Ionosphere & Climate (FORMOSAT-3/COSMIC) has demonstrated the value of GPS-RO data in terrestrial weather, space weather, and climate study. The RO measurement technique was dubbed as "the most accurate and stable thermometer in space" because of its high accuracy, high vertical resolution, and high stability, which does not require calibration. Since its launch in 2006, FORMOSAT-3/COSMIC has accumulated over 6.9 million atmospheric and 4.6 million ionospheric RO sounding profiles. Encouraged by the success of FORMOSAT-3/COSMIC, Taiwan's National Space Organization (NSPO, https://www.nspo.narl.org.tw/index.php?ln=en) and the U.S. National Oceanic and Atmospheric Administration (NOAA) started the planning for the FORMOSAT-7/COSMIC-2 mission in 2008 as a follow-on program to FORMOSAT-3/COSMIC. The FORMOSAT-7/COSMIC-2 satellite constellation, consisting of six small satellites, was successfully launched in June 2019 as the world's first operational RO satellite constellation focusing over the tropics. After fourteen years in service, providing valuable data to operational and research communities, FORMOSAT-3/COSMIC was officially decommissioned ten months after FORMOSAT-7/COSMIC-2 has been sent to space, and replaced by the FORMOSAT-7/COSMIC-2. As expected, the first results from FORMOSAT-7/COSMIC-2 showed positive impact on operational weather prediction and has observed interesting phenomenon in the ionosphere. In this paper, we will summarize the progress from FORMOSAT-7/COSMIC-2 up to date. [ABSTRACT FROM AUTHOR]

Long-term stability, global coverage and high resolution are characteristics that make the Global Navigation Satellite System (GNSS) radio occultation (RO) technique well-suitable to serve as anchor measurements for observing the Earth's atmosphere. The concept of occultation soundings utilizes a receiver placed on a low Earth orbit to measure the accumulated atmospheric contribution along the limb in terms of a phase delay. A high sampling rate allows to reconstruct profiles of geophysical parameters through an inversion process of occultation signals. However, such measurements require a careful processing in order to provide accurate retrievals in the neutral atmosphere. The following development describes specific aspects in radio occultation methodology implemented in the retrieval chain from phase data to profiles of dry pressure and dry temperature. Independent retrievals from nearreal time measurements are compared with occultation products provided by official processing centers to demonstrate reliability of the solution. The region within the upper troposphere and lower stratosphere (UTLS) is particularly represented by a low uncertainty being within 0.5% (K). A comparison with radiosondes shows a significant contribution of a water vapor term in the lower troposphere that comes from the dry air assumption in occultation profiles of pressure and temperature. Radiosonde measurements reproduced to refractivity profiles show very high agreement with occultation soundings, which is generally below 5%. A superior accuracy of RO refractivity is observed in the upper troposphere, where retrievals are consistent with radiosondes to 1%. [ABSTRACT FROM AUTHOR]

A three-dimensional ray tracing model with aiming algorithms for global positioning system (GPS) signal is proposed to make simulations conform to the realistic radio occultation (RO) signal propagation. The two aiming algorithms used in this study ensure the initial and end point ray trajectories are located in the prescribed region. In past studies, the ray tracing techniques applied to the RO signal simulation usually assumed a spherically symmetrical atmosphere for simplicity. The exact GPS and low earth orbit (LEO) satellite locations are not considered in the simulation. These two assumptions make the simulation unrealistic for GPS signal propagation in the RO technique. In the proposed model, the shape of the earth is assumed as an ellipse. The information from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is used to setup the atmosphere in the simulation. Two aiming algorithms are developed to determine the initial signal propagating direction to make the simulated signal start from the prescribed GPS satellite position and end in the close vicinity of the LEO satellite position. An ideal spherical symmetric atmospheric structure is used to verify the ray tracing model. The fractional difference between real and simulated refractivity results is less than 0.1%. Otherwise, the GPS and LEO satellite position in the Formosat-3/COSMIC observation and the ECMWF analysis, considering the earth's flattening, is also used to verify the aiming algorithms. All of the simulated signals end in close vicinity to the LEO satellite position in the simulation results. [ABSTRACT FROM AUTHOR]

Six identical micro-satellites of the FORMOSAT-3/COSMIC (Formosa Satellite #3 and Constellation Observing System for Meteorology, Ionosphere and Climate: FS-3/C) mission were successfully launched on 14 April 2006. The FS-3/C mission provides the first satellite constellation for monitoring global weather using the Global Positioning System (GPS) radio occultation (RO) technique. The mission's primary scientificific goal is to obtain near-real time profiles of the bending angle and refractivity in the neutral atmosphere and in the ionosphere. In April, 2007 the FS-3/C mission provide about RO soundings of 2000 atmospheric vertical profiles per day in a nearly uniform distribution around the globe. The lowest altitude penetration for more than 80% of RO soundings reached below 1 km in altitude. Most soundings have penetration below 800 m altitude in the equatorial region and below 200 m altitude in polar regions. The quality and accuracy of the RO sounding profiles are in good agreement with the CHAMP (CHAllenging Minisatellite Payload) RO soundings and direct measurements using dropsondes. The FS-3/C RO sounding observations are used to support operational global weather prediction, climate monitoring and research, space weather forecasting, and ionosphere and gravity research. [ABSTRACT FROM AUTHOR]

The Taiwan/US FORMOSAT-3/COSMIC (FORMOsa SATellite mission - 3/Constellation Observing System for Meteorology, Ionosphere and Climate) satellite constellation was successfully launched on 14 April 2006. It is expected to leverage the use of the GPS (Global Positioning System) radio occultation data for atmospheric and ionospheric research to improve global weather forecasts and aid climate change related studies. FORMOSAT-3/COSMIC, together with the European MetOp, German CHAMP and US/German GRACE-A satellites, form a 9 satellite constellation for precise atmospheric sounding on a global scale. This satellite constellation is expected to provide about 3500 occultation measurements daily. Recent results and the status of the CHAMP and GRACE-A orbit and occultation data analysis are reviewed and complemented with a review of initial results from FORMOSAT-3/COSMIC at GFZ. The significantly increased potential of the CHAMP, GRACE-A and FORMOSAT-3/COSMIC constellation for atmospheric studies, compared to single satellite missions, is demonstrated for selected applications such as global monitoring of water vapor distributions, tropopause parameters and ionospheric irregularities. [ABSTRACT FROM AUTHOR]

The FORMOSAT-3/COSMIC spacecraft constellation consisting of six LEO satellites is the world's first operational GPS Radio Occultation (RO) mission. The mission is jointly developed by Taiwan's National Space Organization (NSPO) and the United States' UCAR in collaboration with NSF, USAF, NOAA, NASA, NASA's Jet Propulsion Laboratory, and the US Naval Research Laboratory. The FORMOSAT-3/COSMIC satellites were successfully launched from Vandenberg US AFB in California at 0140 UTC 15 April 2006 into the same orbit plane of the designated 516 km altitude. The mission goal is to deploy the six satellites into six orbit planes at 800 km altitude with a 30-degree separation for evenly distributed global coverage. All six FORMOSAT-3/COSMIC satellites are currently maintaining a satisfactory good state-of-health. Five out of six satellites have reached their final mission orbit of 800 km as of November 2007. The data as received by FORMOSAT-3/COSMIC satellites constellation have been processed in near real time into 2500 good ionospheric profiles and 1800 good atmospheric profiles per day. These have outnumbered the worldwide radiosondes (∼900 mostly over land) launched from the ground per day. The processed atmospheric RO data have been assimilated into the Numerical Weather Prediction (NWP) models for real-time weather prediction and typhoon/hurricane forecasting by many major weather centers in the world. This paper describes the FORMOSAT-3/COSMIC satellite constellation system performance and the mission results that span the period from April 2006 to October 2007; and reviews the prospect of a future follow-on mission. [ABSTRACT FROM AUTHOR]