Microwavephysics and Atmospheric Physics
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Biomedizinische Photonik
Ultrafast Science and Technology
Last update: 22.11.2018
FS 2015: Seminare über Microwavephysics and Atmospheric Physics
Friday 10-12
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Freitag, 27.02.2015

Improved Understanding of Thermosphere-Mesosphere-Stratosphere-Troposphere Coupling Using Lidar Measurements

Zeit: 10:15 Uhr
Hörsaal: A97
Prof. Dr. Robert J. Sica
The University of Western Ontario, Canada
MeteoSwiss, Payerne

Solar-terrestrial relations is the study of how solar radiation and particles enter and interact with Earth's atmosphere-ionosphere-magnetosphere system. The atmospheric component of solar-terrestrial relations traditionally emphasizes the interaction of solar energy with the middle and upper atmosphere. Over the last 20 years it has been realized that the coupling of the lower atmosphere with the upper atmosphere is critical to understanding climate and weather on the surface. Thus, simultaneous measurements over a wide range of heights are necessary to provide the inputs needed to understand coupling processes between atmospheric regions.

Active sensing techniques such as radar and lidar (laser radar) allow this coupling to be investigated over a wide range of heights. My group's primary research tool is the Purple Crow Lidar (PCL), which measures atmospheric composition and temperature from near the surface to the lower thermosphere (altitudes above 100 km). The PCL uses a 2.6 m diameter liquid mirror telescope coupled with a high-power laser transmitter to measure temperature, density and water vapour mixing ratio. Due to its large power-aperture product, several of its measurement capabilities are unique, such as the ability to resolve individual gravity waves and measure water vapour in the upper troposphere and lower stratosphere. In addition to the PCL, my group actively collaborates with two other lidar systems located in the high Arctic as part of the Canadian Network for the Detection of Atmospheric Change (CANDAC). Comparison of these measurements with the PCL contributes to understanding teleconnections between high and low latitudes.

The role of small scale waves on the atmospheric system will be discussed and examples will be shown of measurements we have made that demonstrate atmospheric coupling, as well as the transport of atmospheric constituents such as ozone and pollutants between the troposphere and stratosphere. My current research interest is to extract additional information from lidar measurements using an inversion approach, in particular the Optimal Estimation Method (OEM). While OEM has been widely used on passive remote sensing measurements, my collaborator Dr. A. Haefele (MétéoSuisse) and I have recently applied these techniques to the retrieval of temperature and water vapour from lidar measurements. Results will be shown which demonstrate how OEMs can resolve some long-standing issues in the interpretation of the measurements.

Freitag, 20.03.2015

Presentation of Bachelor Theses:
Antenna Pattern Analysis and Optimization for the SRT Radio Telescope
Characterization of different USRP FFT Spectrometers

Zeit: 10:15 Uhr
Hörsaal: A97
Jonathan Gasser
Patricia-Odette Walder
Institute of Applied Physics
University of Bern

The SRT radio telescope is equipped with a cup-feed with adjustable choke ring. This BSc thesis shows antenna simulations with CHAMP and GRASP software for different configurations of the telescope and feed, and compares them with antenna measurements in the current configuration.

The USRP N210 is used as FFT spectrometer in several instruments at IAP. The latest USRP generation X300 provides more processing power, bandwidth and dynamic range. This BSc thesis compares the performance and the filter characteristics of the two USRP generations.

Freitag, 27.03.2015

Presentation of master thesis: Development of a low cost 11 GHz Ozone Radiometer

Zeit: 10:15 Uhr
Hörsaal: A97
Lampros Kosmopoulos
Institute of Applied Physics
University of Bern

In the past, variations of ozone have been successfully observed remotely in the millimeter wavelength. The GROMOS radiometer, operated at the University of Bern, is a successful example. In the case of the millimeter wave lines, the thermal Doppler line width starts to dominate the pressure broadening at an altitude of about 75 km, rendering the retrieval of ozone volume mixing ration strenuous. At the same time, Doppler width for the 11 GHz Ozone line is reduced by a factor of 10, at this altitude. Moreover, atmospheric opacity, which is mainly to water vapor, is much lower for 11 GHz. Despite the much weaker line, compared to the millimeter wave lines, remote observations are possible at ground sites under almost all weather conditions.

In Europe, satellite receivers operate approximately in the 10-12GHz frequency band. The specific frequency that we try to detect, the rotational transition of Ozone (O3) at 11.0724545 GHz, lies within this band. For that reason it is easy to find in the European market satellite components, that can be repurposed for the construction of an 11 GHz radiometer, which can perform efficiently in the Ku-Band (10.7 to 12.75 GHz). But this comes with a price to pay, which in our case is Radio Frequency Interference.

Freitag, 17.04.2015

Measuring with an X-band Doppler-polarimetric weather radar. An enhanced view of precipitation

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Jordi Figueras i Ventura

For years weather radars were single polarization and mostly operating at S (10 cm wavelength) or C (5 cm wavelength) bands. Research in applications of polarimetry for weather radar started in the 70s of the last century although its use is just now being introduced in operational radars. The use of polarimetry has greatly improved the accuracy of higher frequency radars (3 cm wavelength and smaller) up to the point that they exhibit similar or better performance than the traditional ones. Using higher frequency allows for smaller systems which can be mobile. This facilitates their use in specialized applications beyond the traditional weather surveillance by being able to tailor specific scanning strategies.This presentation will provide an overview of the principles of polarimetry applied to weather radar and discuss applications of increasing complexity, from data quality monitoring to hydrometeor classification, drop size distribution retrieval and storm tracking illustrated with data from the MeteoSwiss operated DX50 radar.

Freitag, 24.04.2015

Seminar is cancelled

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Dietrich Feist
Max Planck Institute for Biogeochemistry
Jena, Germany

Freitag, 01.05.2015

Applying millimeter-wave spectroscopy to ground-based remote sensing of the Arctic stratosphere

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Niall Ryan
Universität Bremen

This talk presents the general results of my thesis project while working at the University of Toronto, Canada, which are divided into two main parts: The first part involves the design of a ground-based SIS radiometer and the characterisation of inversions in the 265-280 GHz atmospheric spectral window, in which the instrument was designed to operate. I will show the different effects that spectroscopic parameters have on the inversion of spectra from different gases, and the effect that inversion nonlinearity can have on trend analysis and climatologies. The second part shows two new stratospheric ozone datasets, retrieved with measurements from ground-based radiometers housed at the Swedish Institute for Space Physics (IRF), Kiruna. The datasets are compared to satellite and balloon measurements, and show an interesting ozone feature at approximately 35 km altitude.

Freitag, 29.05.2015

Results from GROMOS-C, the GRound based Ozone MOnitoring System for Campaigns

Zeit: 10:15 Uhr
Hörsaal: A97
Susana Fernandez
Institute of Applied Physics
University of Bern

We have built a new ground based compact microwave radiometer which incorporates different calibration methods and can be operated at remote places with no maintenance requirements. It has been conceived to measure the vertical profile of ozone distribution in the middle atmosphere, by observing pressure broadened emission spectra at a frequency of 110.836 GHz. It can also be switched in frequency to observe the CO line at 115.271 GHz. In addition, wind profiles can be retrieved, based on the Doppler shift of the ozone line. In the first measurement campaign GROMOS-C was located at the Sphinx station at Jungfraujoch, at an altitude of 3580 m. Ozone emission spectra were recorded from January to March 2014. In May 2014 the radiometer was installed in La Réunion island, located in the Indian ocean, where spectra were continuously recorded during 6 months. Vertical profiles have been retrieved from this data and validated against equivalent profiles from Aura MLS satellite and ECMWF model data. In addition, we compare with the ozone lidar located in the observatory and with ozone profiles from weekly radiosondes. Results show that GROMOS-C can provide ozone profiles between 30 to 0.03 hPa (23 to 70 km). The accordance with MLS is within 10% for pressure altitudes between 30 and 0.3 hPa. The comparison with lidar and radiosondes profiles shows a very good agreement for layers between 20 and 5 hPa. A description of the main characteristics of GROMOS-C will be presented, along with the main results from both campaigns

Montag, 08.06.2015

Study of atmospheric water over Bern by means of ground-based observations and numerical simulations

Zeit: 14:00 Uhr
Hörsaal: B6
Federico Cossu
Institute of Applied Physics
University of Bern

Donnerstag, 30.07.2015

Ground-based Doppler microwave radiometry for middle-atmospheric wind profiles

Zeit: 14:00 Uhr
Hörsaal: B5
Rolf Rüfenacht
Institute of Applied Physics
University of Bern