Abstract
Abstract. Stratospheric ozone is of major interest as it absorbs most harmful UV radiation from the sun, allowing life on Earth. Ground-based microwave remote sensing is the only method that allows for the measurement of ozone profiles up to the mesopause, over 24 hours and under different weather conditions with high time resolution. In this paper a novel ground-based microwave radiometer is presented. It is called GROMOS-C (GRound based Ozone MOnitoring System for Campaigns), and it has been designed to measure the vertical profile of ozone distribution in the middle atmosphere by observing ozone emission spectra at a frequency of 110.836 GHz. The instrument is designed in a compact way which makes it transportable and suitable for outdoor use in campaigns, an advantageous feature that is lacking in present day ozone radiometers. It is operated through remote control. GROMOS-C is a total power radiometer which uses a pre-amplified heterodyne receiver, and a digital fast Fourier transform spectrometer for the spectral analysis. Among its main new features, the incorporation of different calibration loads stands out; this includes a noise diode and a new type of blackbody target specifically designed for this instrument, based on Peltier elements. The calibration scheme does not depend on the use of liquid nitrogen; therefore GROMOS-C can be operated at remote places with no maintenance requirements. In addition, the instrument can be switched in frequency to observe the CO line at 115 GHz. A description of the main characteristics of GROMOS-C is included in this paper, as well as the results of a first campaign at the High Altitude Research Station at Jungfraujoch (HFSJ), Switzerland. The validation is performed by comparison of the retrieved profiles against equivalent profiles from MLS (Microwave Limb Sounding) satellite data, ECMWF (European Centre for Medium-Range Weather Forecast) model data, as well as our nearby NDACC (Network for the Detection of Atmospheric Composition Change) ozone radiometer measuring at Bern.
Highlights
Stratospheric ozone protects and allows life on Earth since it filters most of the harmful ultraviolet radiation emitted by the sun
This frequency was chosen over the stronger line at 142.175 GHz because it is less affected by water vapour fluctuations, and the observation of a lower frequency allows for the retrieval of higher altitudes as Doppler broadening is smaller for lower frequencies
GROMOS-C horn antenna was connected to the vector network analyzer (VNA) receiver, and with this configuration we measured the received radiation during a sweep of the waveguide in x and y
Summary
Stratospheric ozone protects and allows life on Earth since it filters most of the harmful ultraviolet radiation emitted by the sun. Ground-based microwave radiometry is the only method that allows for the measurement of ozone profiles up to the mesopause, during 24 h and under different weather conditions, with high temporal resolution. Microwave radiometry is a passive technique based on the detection and analysis of radiation emitted by molecules undergoing rotational transitions in the millimetre wave range In this frequency range, ozone presents two main emission lines which are typically used for radiometry: 110.8 and 142.2 GHz. The transition strength of these lines leads to fairly strong line emission throughout the stratosphere and mesosphere (Fig. 1). Vertical profiles have been retrieved from this data and validated against equivalent profiles from satellite and model data, as well as our ozone radiometer measuring at Bern in the frame of NDACC (GROMOS), located 60 km north-west.
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