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| Titel |
Empirical model for mean temperature for Indian zone and estimation of precipitable water vapor from ground based GPS measurements |
| VerfasserIn |
C. Suresh Raju, K. Saha, B. V. Thampi, K. Parameswaran |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 25, no. 9 ; Nr. 25, no. 9 (2007-10-02), S.1935-1948 |
| Datensatznummer |
250015908
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| Publikation (Nr.) |
 copernicus.org/angeo-25-1935-2007.pdf |
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| Zusammenfassung |
| Estimation of precipitable water (PW) in the atmosphere from ground-based
Global Positioning System (GPS) essentially involves modeling the zenith
hydrostatic delay (ZHD) in terms of surface Pressure (Ps) and subtracting
it from the corresponding values of zenith tropospheric delay (ZTD) to estimate
the zenith wet (non-hydrostatic) delay (ZWD). This further involves
establishing an appropriate model connecting PW and ZWD, which in its simplest
case assumed to be similar to that of ZHD. But when the temperature variations
are large, for the accurate estimate of PW the variation of the
proportionality constant connecting PW and ZWD is to be accounted. For this a
water vapor weighted mean temperature (Tm) has been defined by many
investigations, which has to be modeled on a regional basis. For estimating
PW over the Indian region from GPS data, a region specific model for
Tm in terms of surface temperature (Ts) is developed using the
radiosonde measurements from eight India Meteorological Department (IMD)
stations spread over the sub-continent within a latitude range of 8.5°–32.6° N.
Following a similar procedure Tm-based models are also
evolved for each of these stations and the features of these site-specific
models are compared with those of the region-specific model. Applicability
of the region-specific and site-specific Tm-based models in retrieving
PW from GPS data recorded at the IGS sites Bangalore and Hyderabad, is
tested by comparing the retrieved values of PW with those estimated from the
altitude profile of water vapor measured using radiosonde. The values of
ZWD estimated at 00:00 UTC and 12:00 UTC are used to test the validity of the
models by estimating the PW using the models and comparing it with those
obtained from radiosonde data. The region specific Tm-based model is
found to be in par with if not better than a similar site-specific
Tm-based model for the near equatorial station, Bangalore. A simple
site-specific linear relation without accounting for the temperature effect
through Tm is also found to be quite adequate for Bangalore. But for
Hyderabad, a station located at slightly higher latitude, the deviation for
the linear model is found to be larger than that of the Tm-based model.
This indicates that even though a simple linear regression model is quite
adequate for the near equatorial stations, where the temperature variations
are relatively small, for estimating PW from GPS data at higher latitudes
this model is inferior to the Tm-based model. |
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