KIMRA is a millimeter wave radiometer at the Swedish Institute of Space Physics, Kiruna, Sweden. The location of the instrument (67.8 N, 20.4 E) allows continuous observation of the evolution of ozone and other trace gases in the Arctic stratosphere. It is designed for measurements of thermal emission lines between 195 and 233GHz. Observation of stratospheric ozone and mesospheric carbon monoxide is performed continuously. Signatures of chlorine monoxide, nitrous oxide, and nitric acid are also located in this frequency range. However, due to instrumental effects these signatures are impossible to resolve with KIMRA. From the measurements profiles between 18 and 80km altitude can be retrieved.
The millimeter wave radiometer KIMRA at IRF performs continuous observation of atmospheric trace gases between 18 and 80km). As a monitoring instrument it is important to keep breaks in the operation due to maintenance as short as possible. The main reason for maintenance is the exchange of the cooling unit when cooling performance is decreasing. KIMRA is cooled down to around 24K in order to reduce noise of the detector and first amplifier. The performance of the refrigerator decreases over time until it is due for service. The test chamber aimed for in this project should enable to check the refrigerator performance after service. In order to test the refrigerator's capacity it will be tested with a load which produces heat under controlled conditions.
This project includes both mechanical design of a high vacuum chamber, electronical components and interfaces to test the performance of the refrigerator and development of an operational procedure for a standard test together with a comprehensive test report allowing to repeat the tests.
The work with the millimeter wave radiometers sometimes includes the variation of the RF power to the system input. This is provided by an amplifier with a subsequent attenuator. The attenuator chain is electronically controlled.
The goal for this project is a box with which the attenuator can be controlled manually with a display presenting the actual attenuation. For later usage in automatic test runs the control box should also provide a eithernet connector and a RS232 connector in order to communicate with the box via computer programs.
The student uses available PCB layout of an attenuator switch-driver and creats a user-friendly interface for easy mechanical switching.
This project involves:
- practical work (soldering components to a PCB board)
- design of an electronic circuit for addressing and controlling the attenuators including communications interface (eithernet, RS-232)
- layout of an easy-to-use front end including switches and display.
Under certain circumstances the local oscillator (LO) of the KIMRA instrument causes severe disturbances in the measurements due to some harmonics which are detected by the very sensitive detector. A construction of two metall meshes placed a short distance from each other might be an effective way to attenuate the disturbance. The project work would contain the design construction and test of the meshes in the KIMRA optical path.
The KIMRA system has been complemented by a high resolution Fast-Fourier-Transform spectrometer aiming for the measurement of mesospheric CO and ozone. This state-of-the-art FFT spectrometer is built on a completely new technique for spectrometers and will most likely substitute commonly used techniques in the field of frequency resolving spectrometers. The measurements of both KIMRA spectrometers will be compared. A robust method to merge both spectra will be developed in order to increase the frequency resolution in the spectra.
During the Swedarp 04/05 expedition to the Swedish Antarctic station Wasa a differential optical absorption spectrograph (DOAS) was tested at Wasa. The data can be analysed with the WinDOAS-tool. Since the measurement period at Wasa was considered a feasibility study there could also be a part of this diploma thesis dealing with the design that is necessary in order to run a DOAS instrument at Wasa continuously including snow protection, energy managment, remote control and data transfer via satellite.
At IRF two millimeter wave radiometers are deployed, using three Fast-Fourier-Transform spectrometer (FFTS) and two acousto-optical spectrometer (AOS). This project work aims to assess the channel response function of each of the spectrometers. The work starts with a measurement phase where a very narrow signal from a signal generator to the spectrometer under test sweeps through a certain spectral range at different intensity levels while the spectrometer registers the intensities. In the analysis phase a suitable matlab program presents the channel response. A comparison of the different channel responses concludes the work.
The KIMRA data analysis needs, among others, a temperature profile as input data. The temperature profile has a direct influence on the spectroscopy and the retrieval process that provides the final vertical profile for the trace gas, such as Ozone or Carbon Monoxide. The better the temperature profile the better the results. There are different data sets that are used in the atmospheric science community (such as NCEP, ECMWF, MSIS, ...), measurements with balloon-sondes or even satellite measurements (from MLS, Odin, SABER, ...). The KIMRA data analysis reaches up to very high altitudes (80 - 90 km) and therefore needs a temperature profile stretching roughly from the ground to 110 km. The task of this project would be to assess the available temperature data sets, merge different data sets in an appropriate way and estimate the errors of this procedure. Finally a data base of temperature profiles for the period of available KIMRA measurements shall be established.
In order to estimate polar winter ozone loss from KIMRA measurements it is important to identify the measurement location with respect to the polar vortex. Measurements outside the vortex may contain ozone rich air from lower latitudes and would thus lead to a lower ozone loss estimate as if only inside polar vortex air is considered. Polar vortex data are available for instance from ECMWF (European Center for Medium Range Weather Forecast) and can be used to also graphically present the location of KIMRA measurements in relation to the polar vortex location. For KIMRA data analysis a data base with polar vortex information should be established for the entire period with KIMRA measurements.