HAMSTRAD-Tropo, A 183-GHz Radiometer Dedicated to Sound Tropospheric Water Vapor Over Concordia Station, Antarctica

Abstract

International audienceThe H2O Antarctica Microwave Stratospheric and Tropospheric Radiometers (HAMSTRAD) program aims to develop two ground-based microwave radiometers to sound tropospheric and stratospheric water vapor (H2O) above Dome C (Concordia Station), Antarctica (75??06' S, 123??21'E, 3233 m asml), an extremely cold and dry environment, over decades. By using state-of-the-art technology, the HAMSTRAD-Tropo radiometer uses spectral information in the domains 51-59 GHz (oxygen line) and 169-197 GHz (water vapor line) to derive accurate tropospheric profiles of temperature (with accuracy ranging from 1 to 2 K) and low absolute humidity (with accuracy ranging from 0.02 to 0.05 g ?? m-3), together with integrated water vapor (with accuracy of about 0.008 kg ?? m-2) and liquid water path. Prior to its installation at Dome C in January 2009, the fully automated radiometer has been deployed at the Pic du Midi (PdM, 42??56'N, 0??08'E, 2877 m asml, France) in February 2008 and was in operation for five months. Preliminary comparisons with radio soundings particularly launched in the vicinity of PdM in February 2008 and the outputs from the mesoscale MESO-NH model show a great consistency to within 0.2-0.3 g ?? m-3 between all absolute humidity data sets whatever the atmosphere considered (extremely dry or wet)

Summer to Winter Diurnal Variabilities of Temperature and Water Vapour in the Lowermost Troposphere as Observed by HAMSTRAD over Dome C, Antarctica

“…Considering theoretical calculations (Ricaud et al 2010a) and actual measurements performed at the Pic du Midi (Ricaud et al 2010b) and Dome C , the derived accuracies of the HAMSTRAD individual measurements of temperature and H 2 O below 200 m in a boundary-layer measurement mode (namely measuring at very low elevation angles) are about 0.25-1.0 K and 0.01-0.03 g m −3 , respectively. From theoretical calculations (Ricaud et al 2010a), the vertical resolution of temperature and H 2 O vertical profiles is expected to be about 50 m and 100 m, respectively.…”

“…The HAMSTRAD-Tropo (hereafter named HAMSTRAD) radiometer has already been presented in Ricaud et al (2010a). To sum up, it is a state-of-the-art microwave radiometer dedicated to the measurement of tropospheric H 2 O at 169-197 GHz (G-band, strong water vapour line at 183.3 GHz), together with tropospheric temperature from the oxygen (O 2 ) line (51-59 GHz, V-band, lower frequency wing of the O 2 line), in a very cold and dry environment such as that encountered at Dome C all through the year.…”

“…From theoretical calculations (Ricaud et al 2010a), the vertical resolution of temperature and H 2 O vertical profiles is expected to be about 50 m and 100 m, respectively. The vertical resolution of the HAMSTRAD measurements below 200 m has been revisited considering the January-June 2010 measurements to be 10-20 m for temperature and 25-50 m for H 2 O (see the Appendix).…”

Electromagnetic Spectrum and Remote Information

“…9.4.1.1, measurements are required in the opaque intervals when information has to be gained on meteorological parameters, such as temperature 7 Section 4.1.2.5 mentions that the gaseous atmosphere is an inhomogeneous medium, but the variations of its permittivity are so smooth that it can be considered locally homogeneous and the geometrical optics approximation (5.38), to which the definition of absorption coefficient refers, can be applied. [92] and oxygen [108] millimeter-wave and microwave absorption peaks.…”

Variabilités de la vapeur d'eau et de la température troposphérique au Dôme C (station Concordia), Antarctique. Partie I : l'instrument Hamstrad

“…Spectre théorique calculé pour un rayonnement atmosphérique atteignant l'altitude de 6000 m (trait tireté), 3000 m (trait pointillé) et le niveau de la mer (trait plein) sur un domaine de fré-quence de 0 à 220 GHz. Le domaine spectral couvert par le radiomètre Hamstrad est représenté en bleu : 51-59 GHz (raie de dioxygène) et 169-197 GHz (raie de vapeur d'eau) (tiré de Ricaud et al, 2010a).…”