Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmin23b..03s&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #IN23B-03
Physics
2499 General Or Miscellaneous, 3399 General Or Miscellaneous, 4599 General Or Miscellaneous
Scientific paper
The 2006 National Research Council (NRC) Decadal Report will stress that future directions for Earth science at NASA/NOAA will focus on achievement of a national strategy for the Earth Sciences that balances international economic competitiveness, protection of life and property, and stewardship of the planet for this and future generations. Because of the urgent need for climate measurements identified in the report, a small group from JPL was formed to explore the science benefits of maintaining GPS receivers in orbit for climate science. This is a particularly timely topic since 7 new GPS-science capable satellites were launched in 2006 (COSMIC 1-6, MetOp1), resulting in 10 GPS-science capable satellites in orbit (including CHAMP, SAC-C, GRACE). For this GPS System-of-Systems, we studied climate observations, ionosphere observations, and ocean science. For climate observations, we simulated a constellation of ten satellites in a configuration similar to COSMIC, and performed a multi-year analysis of how such a constellation would be able to characterize long-term trends in temperature. We find that such a constellation is adequate to compute zonally-averaged, monthly mean temperatures with a precision adequate to address expected climate trends of order ~0.1 K per decade. Such a constellation also has adequate local time coverage to avoid aliasing diurnal cycle trends with global climate trends. The high accuracy and consistency of GPS-based atmospheric retrievals suggests that continuously maintaining an operating constellation of such receivers is an important global observation asset for characterizing long-term climate trends. We also performed a series of simulations to determine the science returns that could be achieved with varying sizes of GPS receiver constellations. This study can be used to consider the advantages of including GPS science receivers on future satellites as dedicated constellations or constellations of opportunity. For ocean science, we assumed each satellite would be equipped with a Toga receiver (now in development under NASA's Instrument Incubator Program), and a steerable 20-dB gain antenna with field of view capable of intercepting all available reflections. The conclusions drawn from this study are as follows: - For atmospheric science, a constellation of 9 satellites in reasonably diverse orbits is enough to satisfy anticipated requirements for climate observations. This can be done with either a dedicated constellation (such as COSMIC) or a constellation of opportunity, which could be formed by placing GPS receivers on all new NASA satellites. - For ionospheric science, the near-term, 10-satellite constellation is sufficient to produce major advances in our understanding of space-weather dynamics and to characterize the global conductivity structure of the ionosphere. An even larger constellation would benefit studies of smaller-scale structures in the ionosphere, such as occur at high latitudes during aurora. - For ocean/ice science, a constellation of six satellites equipped for processing ocean and ice reflections would satisfy basic needs. We would encourage in-space testing of the next generation Toga receiver as soon as possible after its completion in 2008, to validate the instrument and demonstrate the benefits of GPS ocean reflection science. If that flight test is successful, a constellation of six GPS receivers could be built up to perform ocean/ice science.
Heeg Christian
Mannucci Anthony
Sherwood Richard
Zuffada Cinzia
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