Measurements of low amounts of precipitable water vapor by millimeter wave spectroscopy: An intercomparison with radiosonde, Raman lidar, and Fourier transform infrared data

Abstract

[1] Observations of very low amounts of precipitable water vapor (PWV) by means of the Ground-Based Millimeter wave Spectrometer (GBMS) are discussed. Low amounts of column water vapor (between 0.5 and 4 mm) are typical of high mountain sites and polar regions, especially during winter, and are difficult to measure accurately because of the lack of sensitivity of conventional instruments to such low PWV contents. The technique used involves the measurement of atmospheric opacity in the range between 230 and 280 GHz with a spectral resolution of 4 GHz, followed by the conversion to precipitable water vapor using a linear relationship. We present the intercomparison of this data set with simultaneous PWV observations obtained with Vaisala RS92k radiosondes, a Raman lidar, and an IR Fourier transform spectrometer. These sets of measurements were carried out during the primary field campaign of the Earth Cooling by Water vapor Radiation (ECOWAR) project which took place at Breuil-Cervinia (45.9°N, 7.6°E, elevation 1990 m) and Plateau Rosa (45.9°N, 7.7°E, elevation 3490 m), Italy, from 3 to 16 March 2007. GBMS PWV measurements show a good agreement with the other three data sets exhibiting a mean difference between observations of '9%. The considerable number of data points available for the GBMS versus lidar PWV correlation allows an additional analysis which indicates negligible systematic differences between the two data sets.

Intercomparison of atmospheric water vapor soundings from the differential absorption lidar (DIAL) and the solar FTIR system on Mt. Zugspitze

“…For measuring integrated water vapor (IWV) solar Fourier-transform infrared spectrometry (FTIR) was recently shown to be one of the most accurate and precise ground-based remote sensing techniques (Sussmann et al, 2009) and this has been confirmed by follow-on intercomparison studies (Pałm et al, 2010;Schneider et al, 2010): Table 1 in Sussmann et al (2009) shows that FTIR is comparable with or better than other state-of-the-art IWV sounding techniques, such as GPS, microwave radiometers, Raman lidars, or sun photometers (e.g. Morland et al, 2006;Fiorucci et al, 2008). The precision of FTIR for IWV was estimated to be better than 0.05 mm (2.2 %), and perfect matching to radiosonde response characteristics (scatter plot with slope ≡ 1) could be achieved by applying a dedicated Tikhonov-based spectral inversion scheme to the FTIR data; this retrieval was utilized for a harmonized study of the decadal trends in IWV above the Zugspitze and Jungfraujoch FTIR stations (Sussmann et al, 2009).…”

Ground-based stratospheric O<sub>3</sub> and HNO<sub>3</sub> measurements at Thule, Greenland: an intercomparison with Aura MLS observations

“…A detailed discussion of the GBMS observing technique and involved equations can be found in de Zafra (1995) and Fiorucci et al (2008).…”

Technical Note: Harmonized retrieval of column-integrated atmospheric water vapor from the FTIR network – first examples for long-term records and station trends

“…One valuable source of data has turned out to be groundbased microwave radiometry (e.g., Morland et al, 2006;Fiorucci et al, 2008). Such measurements are being carried out to some extent within the NDACC 1 network, which is dedicated to long-term, ground-based, atmospheric sounding observations at many stations around the globe.…”

“…The intercomparison data of BASIL (Raman lidar) and GBMS (microwave) with sondes (9th sand 10th row of Table 1) were taken from Fiorucci et al (2008). Both instruments show slopes very close to 1, very small intercepts and biases below 0.1 mm.…”