Validation of brightness and physical temperature from two scanning microwave radiometers in the 60 GHz O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; band using radiosonde measurements

Francisco Navas-Guzmán,Niklaus Kämpfer,Alexander Haefele

doi:10.5194/amt-9-4587-2016

Abstract

Abstract. In this paper, we address the assessment of the tropospheric performance of a new temperature radiometer (TEMPERA) at 60 GHz. With this goal, an intercomparison campaign was carried out at the aerological station of MeteoSwiss in Payerne (Switzerland). The brightness temperature and the tropospheric temperature were assessed by means of a comparison with simultaneous and collocated radiosondes that are launched twice a day at this station. In addition, the TEMPERA performances are compared with the ones from a commercial microwave radiometer (HATPRO), which has some different instrumental characteristics and uses a different inversion algorithm. Brightness temperatures from both radiometers were compared with the ones simulated using a radiative transfer model and atmospheric profiles from radiosondes. A total of 532 cases were analyzed under all weather conditions and evidenced larger brightness temperature deviations between the two radiometers and the radiosondes for the most transparent channels. Two different retrievals for the TEMPERA radiometer were implemented in order to evaluate the effect of the different channels on the temperature retrievals. The comparison with radiosondes evidenced better results very similar to the ones from HATPRO, when the eight more opaque channels were used. The study shows the good performance of TEMPERA to retrieve temperature profiles in the troposphere. The inversion method of TEMPERA is based on the optimal estimation method. The main advantage of this algorithm is that there is no necessity for radiosonde information to achieve good results in contrast to conventional methods as neural networks or lineal regression. Finally, an assessment of the effect of instrumental characteristics as the filter response and the antenna pattern on the brightness temperature showed that they can have an important impact on the most transparent channels.

Highlights

The importance of the knowledge of the thermal structure for scientific understanding of atmospheric processes is widely recognised
The global Aircraft Meteorological DAta Relay (AMDAR) programme initiated by the World Meteorological Organization (WMO) and its members has been using aircraft temperature measurements for a range of meteorological applications
H0 where T b(θ ) is the brightness temperature at elevation angle θ, T0 is the brightness temperature of the cosmic background radiation, T (h) is the physical temperature at height h, h0 is the altitude at ground, h1 is an upper boundary in the atmosphere, α is the absorption coefficient and τ is the opacity

Summary

Introduction

The importance of the knowledge of the thermal structure for scientific understanding of atmospheric processes is widely recognised. The air temperature plays a crucial role on the dynamical, chemical and radiative processes in the atmosphere. In the lowest part of the atmosphere, temperature profiles are a key input for the weather forecast models. Techniques based on in situ or remote sensing measurements are used nowadays to measure atmospheric temperature profiles. Among the in situ techniques, radiosondes (RSs) are extensively used due to high vertical resolution. The global Aircraft Meteorological DAta Relay (AMDAR) programme initiated by the World Meteorological Organization (WMO) and its members has been using aircraft temperature measurements for a range of meteorological applications (public weather forecasting, climate monitoring and prediction, etc). The aircraft use sensors or the emerging MODE-S method to retrieve the temperature (De Haan, 2011)

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