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  • Copernicus GmbH  (10)
  • 1
    Online Resource
    Online Resource
    Quantification of structural uncertainty in climate data records from GPS radio occultation
    Copernicus GmbH ; 2013
    In:  Atmospheric Chemistry and Physics Vol. 13, No. 3 ( 2013-02-06), p. 1469-1484
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 13, No. 3 ( 2013-02-06), p. 1469-1484
    Abstract: Abstract. Global Positioning System (GPS) radio occultation (RO) has provided continuous observations of the Earth's atmosphere since 2001 with global coverage, all-weather capability, and high accuracy and vertical resolution in the upper troposphere and lower stratosphere (UTLS). Precise time measurements enable long-term stability but careful processing is needed. Here we provide climate-oriented atmospheric scientists with multicenter-based results on the long-term stability of RO climatological fields for trend studies. We quantify the structural uncertainty of atmospheric trends estimated from the RO record, which arises from current processing schemes of six international RO processing centers, DMI Copenhagen, EUM Darmstadt, GFZ Potsdam, JPL Pasadena, UCAR Boulder, and WEGC Graz. Monthly-mean zonal-mean fields of bending angle, refractivity, dry pressure, dry geopotential height, and dry temperature from the CHAMP mission are compared for September 2001 to September 2008. We find that structural uncertainty is lowest in the tropics and mid-latitudes (50° S to 50° N) from 8 km to 25 km for all inspected RO variables. In this region, the structural uncertainty in trends over 7 yr is 〈0.03% for bending angle, refractivity, and pressure, 〈3 m for geopotential height of pressure levels, and 〈0.06 K for temperature; low enough for detecting a climate change signal within about a decade. Larger structural uncertainty above about 25 km and at high latitudes is attributable to differences in the processing schemes, which undergo continuous improvements. Though current use of RO for reliable climate trend assessment is bound to 50° S to 50° N, our results show that quality, consistency, and reproducibility are favorable in the UTLS for the establishment of a climate benchmark record.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-13-1469-2013
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2013
    detail.hit.zdb_id: 2092549-9
    detail.hit.zdb_id: 2069847-1
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  • 2
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    Integrated water vapor above Ny Ålesund, Spitsbergen: a multi-sensor intercomparison
    Copernicus GmbH ; 2010
    In:  Atmospheric Chemistry and Physics Vol. 10, No. 3 ( 2010-02-03), p. 1215-1226
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 10, No. 3 ( 2010-02-03), p. 1215-1226
    Abstract: Abstract. Water vapor is an important constituent of the atmosphere. Because of its abundance and its radiative properties it plays an important role for the radiation budget of the atmosphere and has major influence on weather and climate. In this work integrated water vapor (IWV) derived from the measurements of three satellite sensors, GOME, SCIAMACHY and AMSU-B, two ground based sensors, a Fourier-transform spectrometer (FTIR), a microwave radiometer for O3 (RAM) and IWV inferred from GPS zenith path delay (ZPD) measurements, are compared to radio-sonde measurements above Ny Ålesund, 79° N. All six remote sensors exploit different principles and work in different wavelength regions. All remote sensing instruments reproduce the sonde measurements very well and are highly correlated when compared with the radio-sonde measurements. The ground-based FTIR shows very little scatter of about 10%. The GPS performs similar to the FTIR at all times except for very low IWV, where the scatter exceeds 50% of the measured IWV. The other remote sensing instruments show scatter of about 20% (standard deviation). The ground-based RAM performs similar to the satellite instruments, despite the fact that the retrieval of IWV is just a by-product of this ozone sensor.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-10-1215-2010
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2010
    detail.hit.zdb_id: 2092549-9
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  • 3
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    Validation of GPS atmospheric water vapor with WVR data in satellite tracking mode
    Copernicus GmbH ; 2015
    In:  Annales Geophysicae Vol. 33, No. 1 ( 2015-01-13), p. 55-61
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 33, No. 1 ( 2015-01-13), p. 55-61
    Abstract: Abstract. Slant-integrated water vapor (SIWV) data derived from GPS STDs (slant total delays), which provide the spatial information on tropospheric water vapor, have a high potential for assimilation to weather models or for nowcasting or reconstruction of the 3-D humidity field with tomographic techniques. Therefore, the accuracy of GPS STD is important, and independent observations are needed to estimate the quality of GPS STD. In 2012 the GFZ (German Research Centre for Geosciences) started to operate a microwave radiometer in the vicinity of the Potsdam GPS station. The water vapor content along the line of sight between a ground station and a GPS satellite can be derived from GPS data and directly measured by a water vapor radiometer (WVR) at the same time. In this study we present the validation results of SIWV observed by a ground-based GPS receiver and a WVR. The validation covers 184 days of data with dry and wet humidity conditions. SIWV data from GPS and WVR generally show good agreement with a mean bias of −0.4 kg m−2 and an rms (root mean square) of 3.15 kg m−2. The differences in SIWV show an elevation dependent on an rms of 7.13 kg m−2 below 15° but of 1.76 kg m−2 above 15°. Nevertheless, this elevation dependence is not observed regarding relative deviations. The relation between the differences and possible influencing factors (elevation angles, pressure, temperature and relative humidity) are analyzed in this study. Besides the elevation, dependencies between the atmospheric humidity conditions, temperature and the differences in SIWV are found.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-33-55-2015
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2015
    detail.hit.zdb_id: 1458425-6
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  • 4
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    First results from the GPS atmosphere sounding experiment TOR aboard the TerraSAR-X satellite
    Copernicus GmbH ; 2011
    In:  Atmospheric Chemistry and Physics Vol. 11, No. 13 ( 2011-07-13), p. 6687-6699
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 11, No. 13 ( 2011-07-13), p. 6687-6699
    Abstract: Abstract. GPS radio occultation events observed between 24 July and 17 November 2008 by the IGOR occultation receiver aboard the TerraSAR-X satellite are processed and analyzed. The comparison of 15 327 refractivity profiles with collocated ECMWF data yield a mean bias between zero and −0.30 % at altitudes between 5 and 30 km. Standard deviations decrease from about 1.4 % at 5 km to about 0.6 % at 10 km altitude, however, increase significantly in the upper stratosphere. At low latitudes mean biases and standard deviations are larger, in particular in the lower troposphere. The results are consistent with 15 159 refractivity observations collected during the same time period by the BlackJack receiver aboard GRACE-A and processed by GFZ's operational processing system. The main difference between the two occultation instruments is the implementation of open-loop signal tracking in the IGOR (TerraSAR-X) receiver which improves the tropospheric penetration depth in terms of ray height by about 2 km compared to the conventional closed-loop data acquired by BlackJack (GRACE-A).
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-11-6687-2011
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2011
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  • 5
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    Sporadic 〈i〉E〈/i〉 signatures revealed from multi-satellite radio occultation measurements
    Copernicus GmbH ; 2010
    In:  Advances in Radio Science Vol. 8 ( 2010-10-01), p. 225-230
    Details
    In: Advances in Radio Science, Copernicus GmbH, Vol. 8 ( 2010-10-01), p. 225-230
    Abstract: Abstract. Radio occultation measurements performed by the satellites CHAMP, GRACE and FORMOSAT-3/COSMIC provide a huge data set for atmospheric and ionospheric investigations on a global scale. The data sets are used to extract information on sporadic E layers appearing in the lower ionospheric E region. This is done by analyzing signal amplitude variations of the GPS L1 signal. Sporadic E altitudes in northern midlatitudes found from radio occultation measurements are compared with ground-based ionosonde soundings. A large correlation of sporadic E altitudes from these two techniques is found.
    Type of Medium: Online Resource
    ISSN: 1684-9973
    URL: Article
    DOI: 10.5194/ars-8-225-2010
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2010
    detail.hit.zdb_id: 2135129-6
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  • 6
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    Validation of refractivity profiles derived from GRAS raw-sampling data
    Copernicus GmbH ; 2011
    In:  Atmospheric Measurement Techniques Vol. 4, No. 7 ( 2011-07-27), p. 1541-1550
    Details
    In: Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 4, No. 7 ( 2011-07-27), p. 1541-1550
    Abstract: Abstract. Results from GRAS (GNSS Receiver for Atmospheric Sounding) RO (Radio Occultation) data recorded in RS (Raw Sampling) mode processed at the GFZ (German Research Centre for Geoscience) Potsdam are presented. The experimental processing software POCS-X includes FSI (Full Spectrum Inversion) in order to cope with multi-path regions and enables in connection with RS data to retrieve atmospheric refractivity profiles down to the Earths surface. Radio occultation events observed between 30 September and 30 October 2007 are processed and the retrievals are validated against co-located ECMWF (European Centre for Medium-Range Weather Forecasts) profiles. The intercomparison indicates good quality of the retrieved profiles. In the altitude range 8 to 25 km the standard deviation is below 1 %. The mean deviation in this altitude range tends to be negative. At 30 km the negative bias reaches about −0.4 %. Below 8 km the standard deviation increases, reaching 2.5 % at 2 km. Below 2 km the mean deviation tends to be negative, reaching −1.9 % close to the ground. The negative bias mainly stems from the tropical lower troposphere; there, the negative bias reaches −3 %. The tropospheric penetration depth obtained from RS data shows a vast improvement compared to the tropospheric penetration depth typically obtained from CL (Closed Loop) data; 50 % of all retrieved profiles reach 720 m.
    Type of Medium: Online Resource
    ISSN: 1867-8548
    URL: Article
    DOI: 10.5194/amt-4-1541-2011
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2011
    detail.hit.zdb_id: 2505596-3
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  • 7
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    GPS radio occultation with CHAMP and GRACE: A first look at a new and promising satellite configuration for global atmospheric sounding
    Copernicus GmbH ; 2005
    In:  Annales Geophysicae Vol. 23, No. 3 ( 2005-03-30), p. 653-658
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 23, No. 3 ( 2005-03-30), p. 653-658
    Abstract: Abstract. CHAMP (CHAllenging Minisatellite Payload) and GRACE (Gravity Recovery And Climate Experiment) formed a satellite configuration for precise atmospheric sounding during the first activation of the GPS (Global Positioning System) radio occultation experiment aboard GRACE on 28 and 29 July 2004. 338 occultations were recorded aboard both satellites, providing globally distributed vertical profiles of refractivity, temperature and specific humidity. The combined set of CHAMP and GRACE profiles shows excellent agreement with meteorological analysis. Almost no refractivity bias is observed between 5 and 30km, the standard deviation is between 1 and 2% within this altitude interval. The GRACE satellite clock stability is significantly improved in comparison with CHAMP. This allows for the application of a zero difference technique for precise analysis of the GRACE occultation data.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-23-653-2005
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2005
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  • 8
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    Comparison of ECMWF analyses with GPS radio occultations from CHAMP
    Copernicus GmbH ; 2008
    In:  Annales Geophysicae Vol. 26, No. 11 ( 2008-10-21), p. 3225-3234
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 26, No. 11 ( 2008-10-21), p. 3225-3234
    Abstract: Abstract. A climatological validation of the 6-hourly operational ECMWF troposphere and lower stratosphere temperatures as well as geopotential heights between 1000 and 10 hPa is performed using the 2001–2007 (80 months from May 2001 to December 2007) CHAMP radio occultation data. Generally there is a good agreement between ECMWF and CHAMP temperatures averaged over 300–10 hPa for all years/seasons with global annual mean biases (standard deviations) less than 0.3 (1.7) K. Regional and temporal discrepancies occur within the polar vortex mainly on the Southern Hemisphere and the tropical tropopause region. Global annual mean biases (standard deviations) of geopotential heights between 300 and 10 hPa are in the range of −30 up to +5 (30–50) geopotential meter. Larger deviations from the mean values are also observed in the tropics and polar zones. Both, the biases and standard deviations between CHAMP and ECMWF temperatures and geopotential heights differ significantly before and after February and December 2006, i.e. the dates when ECMWF increased the number of model levels from L60 to L91 (1 February 2006) and where ECMWF became one of the first weather centers assimilating radio occultation data (since 12 December 2006), mainly from the COSMIC mission. At ECMWF the CHAMP data were only assimilated until 4 February 2007, e.g. both data sets are mostly independent from each other during the time period considered here.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-26-3225-2008
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2008
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  • 9
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    Integrated water vapor from IGS ground-based GPS observations: initial results from a global 5-min data set
    Copernicus GmbH ; 2009
    In:  Annales Geophysicae Vol. 27, No. 7 ( 2009-07-16), p. 2851-2859
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 27, No. 7 ( 2009-07-16), p. 2851-2859
    Abstract: Abstract. Ground based GPS zenith path delay (ZPD) measurements are well established as a powerful tool for integrated water vapor (IWV) observation. The International GNSS Service (IGS) provides ZPD data of currently more than 300 globally distributed GPS stations. To derive IWV from these data, meteorological information (ground pressure and mean temperature above the station) are needed. Only a limited number of IGS stations is equipped with meteorological ground sensors up to now. Thus, meteorological data for IWV conversion are usually derived from nearby ground meteorological observations (ground pressure) and meteorological analyses (mean temperature). In this paper we demonstrate for the first time the applicability of ground pressure data from ECMWF meteorological analysis fields in this context. Beside simplified data handling (no single station data and quality control) this approach allows for IWV derivation if nearby meteorological stations are not available. Using ECMWF ground pressure and mean temperature data the new IGS 5-min ZPD data set has been converted to IWV for the first time. We present initial results from selected stations with ground meteorological sensors including pressure and temperature comparisons between ECMWF and local measurements. The GPS IWV is generally validated by comparison with ECMWF IWV. The ECMWF derived station meteorological data are compared with local measurements at all accordingly equipped stations. Based on this comparison, the mean error (in terms of standard deviation) introduced by time interpolation of the 6-hourly ECMWF data is estimated below 0.2 mm IWV.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-27-2851-2009
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2009
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  • 10
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    GPS radio occultation with CHAMP and SAC-C: global monitoring of thermal tropopause parameters
    Copernicus GmbH ; 2005
    In:  Atmospheric Chemistry and Physics Vol. 5, No. 6 ( 2005-06-15), p. 1473-1488
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 5, No. 6 ( 2005-06-15), p. 1473-1488
    Abstract: Abstract. In this study the global lapse-rate tropopause (LRT) pressure, temperature, potential temperature, and sharpness are discussed based on Global Positioning System (GPS) radio occultations (RO) from the German CHAMP (CHAllenging Minisatellite Payload) and the U.S.-Argentinian SAC-C (Satelite de Aplicaciones Cientificas-C) satellite missions. Results with respect to seasonal variations are compared with operational radiosonde data and ECMWF (European Centre for Medium-Range Weather Forecast) operational analyses. Results on the tropical quasi-biennial oscillation (QBO) are updated from an earlier study. CHAMP RO data are available continuously since May 2001 with on average 150 high resolution temperature profiles per day. SAC-C data are available for several periods in 2001 and 2002. In this study temperature data from CHAMP for the period May 2001-December 2004 and SAC-C data from August 2001-October 2001 and March 2002-November 2002 were used, respectively. The bias between GPS RO temperature profiles and radiosonde data was found to be less than 1.5K between 300 and 10hPa with a standard deviation of 2-3K. Between 200-20hPa the bias is even less than 0.5K (2K standard deviation). The mean deviations based on 167699 comparisons between CHAMP/SAC-C and ECMWF LRT parameters are (-2.1±37.1)hPa for pressure and (0.1±4.2)K for temperature. Comparisons of LRT pressure and temperature between CHAMP and nearby radiosondes (13230) resulted in (5.8±19.8)hPa and (-0.1±3.3)K, respectively. The comparisons between CHAMP/SAC-C and ECMWF show on average the largest differences in the vicinity of the jet streams with up to 700m in LRT altitude and 3K in LRT temperature, respectively. The CHAMP mission generates the first long-term RO data set. Other satellite missions will follow (GRACE, COSMIC, MetOp, TerraSAR-X, EQUARS) generating together some thousand temperature profiles daily.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-5-1473-2005
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2005
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