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| Titel |
First results from the GPS atmospheric remote sensing experiment TOR aboard TerraSAR-X |
| VerfasserIn |
G. Beyerle, L. Grunwaldt, S. Heise, W. Köhler, T. Schmidt, K.-R. Choi, G. Michalak, R. König, M. Rothacher, J. Wickert |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022641
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| Zusammenfassung |
| The TerraSAR-X satellite was launched on 15 June 2007 into a sun-synchronous orbit at an
altitude of about 514Â km and about 98-Â orbit inclination. In addition to synthetic aperture
radar and laser communication payloads, TerraSAR-X accommodates the Tracking,
Occultation and Ranging (TOR) experiment. TOR’s hardware consists of the Integrated
Geodetic and Occultation Receiver (IGOR) and a laser retro-reflector for Satellite Laser
Ranging (SLR). IGOR, a dual frequency, geodetic-grade GPS receiver instrument, provides
signal-to-noise ratios, pseudorange and carrier phase observations of an occulting
and a reference satellite at sampling rates of up to 50Â Hz for remote sensing of
atmospheric refractivity using the radio occultation (RO) technique. For precise orbit
determination pseudorange and carrier phase data from all satellites in view are sampled at
0.1Â Hz.
Three brief RO tests were conducted with TOR in 2007; a 32-day campaign was
performed in January/February 2008 and from 25 July to 17 November 2008 occultation
events were recorded continuously for 117Â days. We describe first results from an analysis of
about 19.000 setting radio occultation events observed during that last campaign.
Atmospheric refractivity profiles derived from TOR data are intercompared with ECMWF
analyses; ECMWF analysis data are interpolated to the time and location of the RO
measurement. At altitudes of about 2–25Â km the mean fractional refractivity bias with
respect to ECMWF is less than ±0.5%, its standard deviation varies between 0.5%
and 1% in the altitude range 5–20Â km increasing to about 2% at altitudes below
5Â km and above 20Â km. Unlike the RO receivers aboard the CHAMP and GRACE
satellites the IGOR aboard TerraSAR-X employs an open-loop tracking technique to
improve L1 carrier phase tracking at altitudes below 5 to 6Â km. Consistent with
earlier findings from the COSMIC constellation, open-loop tracking significantly
reduces the 50%-altitude, the tangent point altitude which is reached by 50% of all
setting observations. During the same time period (25Â July 2008 to 17Â November
2008) the RO experiment aboard GRACE-A recorded fewer events (about 16.000).
While GRACE-A results exhibit a significantly smaller standard deviation in the
stratosphere, their 50%-altitude is about 2.3Â km higher than the corresponding
TerraSAR-X result underlining the improved tracking behavior of TOR in the lower
troposphere. |
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