 |
| Titel |
Retrieval of characteristic parameters for water vapour transmittance in the development of ground-based sun–sky radiometric measurements of columnar water vapour |
| VerfasserIn |
M. Campanelli, T. Nakajima, P. Khatri, T. Takamura, A. Uchiyama, V. Estellés, G. L. Liberti, V. Malvestuto |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1867-1381
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 4 ; Nr. 7, no. 4 (2014-04-29), S.1075-1087 |
| Datensatznummer |
250115702
|
| Publikation (Nr.) |
 copernicus.org/amt-7-1075-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
Sun–sky radiometers are instruments created for aerosol study, but they can
measure in the water vapour absorption band allowing the estimation of
columnar water vapour in clear sky simultaneously with aerosol
characteristics, with high temporal resolution. A new methodology is
presented for estimating calibration parameters (i.e. characteristic
parameters of the atmospheric transmittance and solar calibration constant)
directly from the sun–sky radiometer measurements. The methodology is based
on the hypothesis that characteristic parameters of the atmospheric
transmittance are dependent on vertical profiles of pressure, temperature and
moisture occurring at each site of measurement. To obtain the parameters from
the proposed methodology some seasonal independent measurements of columnar
water vapour taken over a large range of solar zenith angle simultaneously
with the sun–sky radiometer measurements, are needed. In this work high time
resolution columnar water vapour measurements by GPS were used as independent
data set, but also the case when such measurements are not available was
considered by developing the surface humidity method (SHM). This methodology
makes it possible to retrieve the needed independent data set of columnar water vapour
using the standard surface meteorological observations (temperature, pressure
and relative humidity) more readily available. The time pattern of columnar
water vapour from sun–sky radiometer retrieved using both the methodologies
was compared with simultaneous measurements from microwave radiometer,
radiosondings and GPS. Water vapour from sun–sky radiometer, obtained using
GPS independent measurements, was characterized by an error varying from
1% up to 5%, whereas water vapour from SHM showed an error from
1% up to 11%, depending on the local columnar water occurring at
the site during the year. These errors were estimated by comparing water
vapour series from sun–sky radiometer against measurements taken by GPS at a
nearby station. The accordance between retrievals from sun–sky
radiometer and simultaneous measurements from the other instruments was found
always within the error both in the case of SHM and of the GPS independent
data set.
Water vapour obtained using characteristic parameters of the atmospheric
transmittance dependent on water vapour was also compared against GPS
retrievals, showing a clear improvement with respect to the case when these
parameters are kept fixed. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|