Deriving the tropospheric integrated water vapor from tipping curve–derived opacity near 22 GHz

Abstract

[1] In this study we present a simple relation between the tropospheric opacity t near 22.235 GHz and the integrated water vapor (IWV) content of the troposphere. The opacity is measured at Bern, Switzerland, by the radiometer Middle Atmospheric Water Vapour Radiometer (MIAWARA), designed for middle atmospheric water vapor profile measurements. In contrast to typical radiometers for tropospheric monitoring, this middle atmospheric water vapor radiometer only measures in the vicinity of the 22.235 GHz water vapor line with a bandwidth of 1 GHz. With this study we show that it is even possible to derive the integrated tropospheric water vapor (IWV) content of the atmosphere using this limited frequency range if the liquid water content of the atmosphere is negligible. IWV measurements of the tropospheric monitoring instruments Tropospheric Water Vapour Radiometer (TROWARA, two-channel radiometer), All-Sky Multi Wavelength Radiometer (ASMUWARA, multichannel radiometer), and GPS, which are operated next to MIAWARA, are used to derive a linear relation between the opacity and the water vapor content of the troposphere. In a second step, the mean tropospheric temperature is taken into account and a slight improvement of the linear relation is achieved. All instruments involved in this study are contributing to the Studies in Atmospheric Radiative Transfer and Water Vapour Effects (STARTWAVE) project of the Climate program of the National Competence Center in Research. The MIAWARA measurements in the subarctic winter in northern Finland during the Lapbiat Upper Tropospheric Lower Stratospheric Water Vapor Validation Project (LAUTLOS/WAVVAP) campaign in 2004 are compared to radiosonde measurements by the Finnish Meteorological Institute using the same algorithm that was derived for Bern. The agreement of MIAWARA IWV and radiosonde IWV is of the same order as for Bern. Finally, Payerne radiosonde measurements and model simulation using the Atmospheric Radiative Transfer Simulator (ARTS) software and the continuum absorption models of Rosenkranz (1998) and Liebe (MPM87/MPM93) confirm the derived opacity-IWV relation. This study shows that the integrated water vapor content of the troposphere can be measured by a radiometer operating near the 22.235 GHz water vapor line using a bandwidth of 1 GHz, if the liquid water content of the atmosphere is negligible.Citation: Deuber, B., J. Morland, L. Martin, and N. Kämpfer (2005), Deriving the tropospheric integrated water vapor from tipping curve -derived opacity near 22 GHz, Radio Sci., 40, RS5011,

Atmospheric opacity estimation based on IWV derived from GNSS observations for VLBI applications

“…8, we notice that the correlation is consistently high with values between 0.944 and 0.955. The values of the correlation coefficients are very similar to 0.9489 reported by the Deuber et al (2005). The best correlation value was obtained for the PPP solution with GMF and with the Bevis et al (1992) formula to estimate the T m values.…”

“…Based on the opacity measurements at 22 GHz and the atmospheric transmission of microwave (ATM) model, Marvil (2010) Deuber et al (2005), the noticeable difference for both coefficients is seen.…”

“…Deuber et al (2005) presented the correlation between IWV and atmospheric opacity based on the measurements of IWV from three different instruments, i.e. the all-sky multi wavelength radiometer (ASMUWARA), a tropospheric water vapor radiometer, and a GNSS receiver, and the atmospheric opacity from the ground-based radiometer MIAWARA.…”

Retrieval of tropospheric water vapour by using spectra of a 22 GHz radiometer

“…In the frame of investigations concerning the estimation of the integrated water vapour content (IWV) from the opacity measured by MI-AWARA, comparisons with IWV derived from GPS-wet delay showed a tendency of overestimation of the IWV from the MIAWARA opacity when clouds are present. As the IWV is estimated from opacity using a more or less linear relationship (Deuber et al, 2005b), this is likely due to too high opacity measurements. This then could have consequences for the retrieval, mainly leading to an overestimation of the humidity over the entire profile.…”

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

“…Thus, considering a best-case scenario (below 2 mm pwv), the potential observing frequency bands would be 70 − 115 GHz, 120 − 170 GHz, and 206 − 223 GHz. The opacity models were calculated using the CASA (McMullin et al 2007) asap.opacity.model class, and deriving the pwv value from the 22 GHz K-band zenith opacity (Deuber et al 2005, Hiriart & Salas 2007.…”