Examensarbeten för masterexamen // Master Theses
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- PostAnalysis of polarimetric signatures of Arctic lead ice using data from AIRSAR and RADARSAT(2008) Bäck, Daniel; Chalmers tekniska högskola / Institutionen för radio- och rymdvetenskap; Chalmers University of Technology / Department of Radio and Space ScienceIn December 2004 the JPL airborne synthetic aperture radar (AIRSAR) flown on the NASA DC-8 acquired fully polarimetric data in the Beaufort Sea at C, L and P-band. This work presents the backscatter coefficients (σHH, σVV, σHV), copolarized ratios (σHH/σVV) and copolarized phase differences (ϕHH-VV) at the three frequencies from various sea ice types and in particular different young sea-ice types formed in recently frozen leads. Two weeks of RADARSAT imagery from the same region as the AIRSAR data was used in order to identify when and where leads were formed and the age of the newly formed ice contained within the leads. By using a known empirical relationship based on freezing degree days, the thickness of a sea-ice layer could be estimated from its age. Several stages of new and young ice were identified and examined by using RADARSAT imagery to track back in time to find sea-ice openings: lead ice 1-2 days old, lead ice 2-3 days old, lead ice 9-14 days old, lead ice/first year ice older than 15 days and multi-year ice. Furthermore, narrow cracks with unique signatures, hypothesized to be a few hours old, found in several 1-2 days old leads have been included in the analysis. In addition to report the polarimetric signatures of these ice types, this study seeks to find which combination of polarimetric parameters that best differentiates the primary ice types as well as the stages of new and young ice within the leads. Ice that is thought to be less than one day old has the lowest backscatter coefficients for C- and L-band. This ice type also has significantly larger copolar phases for C- band than the other ice types and is the only ice type that shows negative phase differences for L-band, in correspondence with previous reported results for very young ice. Furthermore, it has the lowest observed C-band copolar ratios. Ice 1- 2 days old is characteristic for the large variability of the significantly negative P-band phases. Ice up to three days old has the lowest C-band copolar ratios. Using copolar ratios and phase to discriminate ice of age 9-14 days and older than 15 days was difficult, but L-band backscatter appears to give more contrast. The analysis of the phase information shows large variations between the thin ice types but it is hard to draw unambiguous conclusions. However, generally the phases for thin ice have much larger variability and typically have an offset relative to multi-year ice. The best separations of thin ice are found by using C-band channels and for combinations with different polarizations. C-band crosspolarized backscatter coefficient combined with C-band copolarized ratio has been determined as giving the largest separation causing less misclassification, using a discriminant classifier. Ice less than one day and multi-year ice are the ice types that separate best from the other types while the other ice types more or less overlap for most combinations. Severe mixing between ice types occurs for combination of different L-band channels. In future work the calibration quality of L- and P-band needs to be assessed. More time must be spent on trying to define different ice types and how to pick ice samples minimizing the effect of inhomogenities in the different polarimetric channels. Methods to determine normalized classification accuracies, independent of the number of samples of each class, must be considered.
- PostDigital Receiver for SALSA(2010) Naeem, Umair; Durrani, Nabeel; Chalmers tekniska högskola / Institutionen för radio- och rymdvetenskap; Chalmers University of Technology / Department of Radio and Space ScienceThe SALSA receiver uses a 2.3m parabolic antenna steerable in azimuth and elevation by motor driven mount. A horn with a probe integrated with a Low Noise Amplifier (LNA) is mounted in the focus of the parabola. The horn and the antenna are optimized for 1420 MHz, which is the frequency at which atomic hydrogen in the Milky Way is emitting. This Master thesis, entitled "Digital Receiver for SALSA", describes the upgrade of the existing receiver and antenna control. We designed the new digital receiver system that use a reconfigurable I/O (RIO) FPGA in conjunction with antenna control software and a software receiver (Software-Defined-Radio or SDR). The purpose of upgrading the system was to include some enhancements in the antenna controller as well as in the receiver. In the previous system a C program just worked as a GUI for the user, taking data and sending it to a microcontroller based hardware system, which decodes this data signal and sends appropriate signal to the antenna mount and then reads feedback encoder. In this project, a flexible and scalable software is realized to replace this complicated hardware. In the upgraded receiver, a Antenna Motion Controller software completely controls antenna. The software is designed in such a way that it does not miss even a single feedback pulse (there are 4 feedback pulses in one degree). The accuracy factor of software is 0.25 degrees. The old receiver was hardware-based, thus every new configuration required new hardware. However, in our case, the software receiver is highly flexible in which a wide range of configuration is possible without changing or upgrading existing hardware. The new receiver also works in real-time mode (real-time signal processing) while the old one used to do store-and-process. This upgrade reduces the user interaction to continuously obtain signal spectra, and also minimizes the hardware needs.
- PostEstimation of the absorption of extraterrestrial radio noise using a narrow beam VHF radar at 53.5 MHz in Andenes, Norway(2008) Sadeghi, Seyed Soheil; Chalmers tekniska högskola / Institutionen för radio- och rymdvetenskap; Chalmers University of Technology / Department of Radio and Space ScienceThe Earth’s magnetic field works like a shield against the solar wind flux of plasma, but at the polar regions, where it fails to do so, these charged particles may be guided down to low altitudes and introduce a lot of impacts on the environment, ranging from the nice colourful Aurora, to chemical changes in the atmosphere and decrease in the amount of ozone in the middle atmosphere, and from satellite damages to power line cut offs, depending on the type and energy of the particles. Extraterrestrial HF/VHF radio noise from the universe and mainly from our own galaxy is continuously coming towards our planet. Absorption of these electromagnetic waves in the Earth’s ionosphere is a well known proxy of the events which can enhance it, mainly having direct or indirect root in the solar activities, like Solar Flares, Coronal Mass Ejections, and Geomagnetic Storms and the resulted X rays, Solar Proton Events and Precipitating Energetic charged Particles. Cosmic radio noise power and the corresponding ionospheric absorption is normally measured by the riometers (Relative Ionospheric Opacity Meters for Extraterrestrial Electromagnetic Radiation), and especially in recent years by multiple narrow beam imaging riometers. In this thesis, the data obtained by the vertical beam of a narrow beam MST radar, ALWIN, at Andenes, Norway (69.17°N; 16.01°E) is used as a (narrow beam of a) riometer to estimate the incident cosmic noise power at 53.5 MHz and its absorption, especially during solar/geomagnetic activity periods. The results are in good agreement with riometers (IRIS and AIRIS in Andenes and Kilpisjarvi Finland, 69.06°N, 20.55°E) common volume measurements and with electron density measurements of the Saura MF Radar. The obtained Quiet Day Curves (QDCs) are in very good agreement with theoretical and observed QDCs estimated by Friedrich et al. (2001).
- PostImproving the emissivity model of rough water with GNSS-reflectometry. Correlation of L-band radiometric measurements with GPS-R data.(2011) Mancel, Caroline; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesRemote sensing of sea surface salinity (SSS) is a challenging task. Variations of salinity in oceans are very small, but even minor changes influence the global circulation of water, thus the environment and climate. Those variations are therefore to be monitored with the highest sensitivity possible, and one way to do this is by means of radiometry. Unfortunately, the thermal radiation that is emitted by the sea, and from the measurement of which salinity can be estimated, does not change dramatically with SSS gradients, hence the difficulty to map the global salinity distribution with high accuracy. What’s even more important is the roughness of the sea: increasing roughness leads to additional thermal radiation from the sea, but in a way that is not known and not properly accounted for. As a result, the theory used to model the emissivity of water needs empirical corrections, which can be made by investigating in which manner, and to which extent, the emission of the sea changes with geophysical parameters that characterize this roughness. Those parameters are brought by studying how the signals of the Global Navigation Satellite System (GNSS) are modified when they are reflected at the surface, and methods used to do so define the field of GNSS‐reflectometry (GNSS-R). This thesis investigates how the additional emission of the sea due to its roughness is possibly correlated to GNSS‐R observables. The data considered were collected on two different airborne campaigns, for which the instrumentation onboard was however the same (same radiometer and same GNSS reflectometer). Another campaign was organized during the thesis (different instrumentation onboard though); data of the latter will be processed in the close future, meaning that the work done during this thesis will lead to further research on the same topic. As for the results obtained from the other campaigns, they show that the emission of the sea that is due to the surface roughness is always a linear function of this roughness when correlation is observed. This observation was made for five GNSS‐R observables, out of seven investigated in total. Among those, one is computed from the combination of GNSS‐R measurements with a statistical description of the sea waves: the Mean Squared Slope (MSS). Although correlation is observed for five different observables, it turns out that it is clearest when MSS estimates are considered, indicating that the roughness of the sea is better characterized when GNSS-R measurements are combined with statistical information.
- PostMCM Design of Electromagnetic Field Vector Sensing Radio receiver for Space Applications(2009) Kumar, Kiran; Chalmers tekniska högskola / Institutionen för radio- och rymdvetenskap; Chalmers University of Technology / Department of Radio and Space ScienceMiniaturization of electronics could play an important role in Space applications due to the better thermal and electrical characteristics,very low mass as compared to printed circuit boards (PCB). Since mass is an important cost driver in all space missions, miniaturization may ultimately decrease the cost of satellite. The current work is to upgrade an already existing Electromagnetic field vector sensor (EFVS), on a PCB to Silicon and Low temperature cofired ceramic (LTCC) modules using Multichip module technology (MCM). EFVS is a three channel digital high frequency sampling system, which measures the three-dimensional electric and magnetic fields. MCM is a novel technology used to miniaturize electronics by achieving high density packaging, where multiple bare dies are connected on to the same substrate. The design and layouts for both silicon and LTCC modules has been done and are ready for fabrication. The size of the board has been reduced by 75 percent whereas the mass is expected to be reduced by 90 percent. Chapter 1 deals with the introduction of Microlink-1, a nanosatellite and the different instruments on it, of which EFVS is a constituent. Chapter 2 discusses the measurement principles of 3 dimensional vector fields. Chapter 3 discusses the design and functionality of the EFVS. Emphasis on MCM technology is given in chapter 4. Chapter 5 gives a detailed description of design considerations and design of layouts of both silicon and LTCC modules. A brief description of the fabrication technologies to be used for fabrication of both the modules is presented in chapter 6. The EFVS has applications in Astrophysics, Astroparticle physics, Space Plasma Physics, Low frequency Radio astronomy measuring the three dimensional electric and magnetic fields.