Soundings
11. Jens Wickert |
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CHAMP,
the German geoscience satellite (launched in July 2000), performs GPS
radio occultation measurements. Since February 2001, GFZ Potsdam provides
continuously up to 200 vertical profiles of refractivity, temperature
and water vapor per day. As the CHAMP mission is expected to last at
least until 2007, the first long-term data set of the innovative GPS
radio occultation method is anticipated. Characteristics of the provided
data products are: global coverage, long-term stability, high accuracy
and high vertical resolution.
Processing Scenario: “Near-Real-Time” processing of the atmospheric excess phase for each occultation event (Level 2 data product) with average delay of ~5h between each measurement and provision of the according data product; operational generation of vertical atmospheric profiles (refractivity, temperature, water vapor; Level 3 data products) with ~1-2 days delay between measurement and provision at the GFZ data center.
Planned Application: NWP assimilation and Climate
Scientific Processing: Software package developed in-house (POCS, Potsdam Occultation Software)
Product Evaluation:
Comparison with radio sonde data and meteorological analyses from ECMWF;
Nearly bias free refractivity between 8-35 km in relation to ECMWF (global
average), standard deviation ~1%; bias free temperature 8-25 km (above depending
on the initialization);
Current product version (004) exhibit negative (in relation to ECMWF and radio
sondes) refractivity bias in the middle and lower Troposphere up to ~5% in
the Tropics near the Earth’s surface; next version (currently under development;
005) will show significantly reduced refractivity bias (by a factor of 2-3)
Availability and Exchange: Data are available free, after registration at the GFZ data center; we are interested in additional validation projects and applications of our data.
Website: http://www.gfz-potsdam.de/pb1/GASP/GASP2/index_GASP2.html