Rymd-, geo- och miljövetenskap (SEE) // Space, Earth and Environment (SEE)
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Vi utgår från observationer av universum och vår planet för att utveckla modeller och verktyg som möter globala utmaningar kring resurser, energiförsörjning och klimatpåverkan.
Vart är vi på väg? Var kommer vi ifrån? På vår institution söker vi svaren på de riktigt stora frågorna. I ett långt tidsperspektiv ger stjärnor och galaxers livscykler en inblick i universums, jordens och livets uppkomst – och framtid. Vi observerar också vår planet och samspelet mellan samhälle, teknik och natur för att kunna utveckla teknik, modeller och verktyg som kan möta globala utmaningar inom naturresurser, klimatpåverkan och energiförsörjning.
För forskning och forskningspublikationer, se https://research.chalmers.se/organisation/rymd-geo-och-miljoevetenskap/
Observes the universe and our planet, to develop models and tools that meet global challenges regarding resources, energy supply and climate impact.
Where do we come from and where are we going? At our department we search for answers to the really big questions. In a long time perspective, the lifecycles of stars and galaxies provide an insight into the origin and future of the universe, earth and life. We also observe our planet and the interaction between society, technology and nature in order to develop technologies, models and tools that can meet global challenges regarding natural resources, climate impact and energy supply.
Studying at the Department of Space, Earth and Environment at Chalmers
For research and research output, please visit https://research.chalmers.se/en/organization/space-earth-and-environment/
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Browsar Rymd-, geo- och miljövetenskap (SEE) // Space, Earth and Environment (SEE) efter Program "Communication Engineering (MPCOM), MSc"
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- PostA rapid acquisition GPS receiver based on ultra tightly coupled IMU and GPS(2010) Garcia, Gabriel E.; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesNowadays, the importance to obtain position in weak signal environments, such as indoors, has increased in order to take a step forward in the greater use of GPS. However, the weak signal environment may include several negative factors such as low signal to noise ratio, signal jamming and interference among others that shall be studied. The present thesis work proposes an open loop approach to deal with the signal dynamics. A Doppler model is proposed in order to remove the dynamics of the incoming GPS signal with the aid of an Inertial Measurement Unit (IMU). The model is broken down into calculating the satellite dynamics, the receiver dynamics and the receiver's oscillator dynamics. An error budget is created in order to see the unpredictable errors and their influence. A bandwidth analysis is also performed in order to analyze the effects of the dynamics in the receiver's phase locked loop (PLL), more specifically in the loop bandwidth. Available measurements from a high tech IMU and a GPS receiver oscillator are analyzed to quantify the time dependant errors. An algorithm to account for the satellite dynamics is proposed with an accuracy Doppler error of ±:0005 Hz. It is shown that the errors from the IMU are dominant in the error budget. However, the receiver dynamics errors are reduced: For a scenario where a vehicle enters a tunnel at 100 km/h and 50 seconds later exits the tunnel with a speed of 28 km/h it is shown that the dynamics of the signal can be reduced from 100 Hz to 6 Hz after implementing the open loop approach. The errors introduced by the oscillator are also shown to be significant with up to 2.58 Hz for L1 GPS signal. These conclusions give arise to the use of lower bandwidth usage in the PLL. Higher signal to noise ratio can be deduced and rapid acquisition and reacquisition of the signal is possible, meaning the GPS signal can be tracked immediately after blockage situations.
- PostAnalysis of static and dynamic GNSS multipath in rural area(2024) Behzadi, Sepehr; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Johansson, Jan; Johansson, JanPresently, the development of autonomous vehicles, particularly in construction, fo cuses extensively on excavators. This thesis examines the impact of multipath and environmental factors on GNSS signals when a single GNSS antenna is mounted on an excavator. Signal Strength Indicator(SSI) data for Galileo and GPS, along side GPS carrier phase residuals from the multi-GNSS PPP software GipsyX, were utilized to analyze the environment’s influence and the effects stemming from the excavator and its arm orientation. The experiment took place at a farm near the Onsala Space Observatory, involving the daily rotation of the excavator’s arm in different directions and simulated digging scenarios. Analysis of GPS SSI data from RINEX files and GPS post-fit residuals unveiled a systematic effect associated with the excavator’s arm orientation. The discernible impact on SSI suggests the potential for predicting the arm’s orientation even be fore data processing. Furthermore, employing residuals enables modeling of effects and errors linked to diverse arm orientations, promising enhanced data processing accuracy. Notably, superior performance was achieved using the L2L signal, demon strating higher correlations among residuals with matching arm orientations. Using the L2L signal also yielded improved repeatability in position estimations. The study suggests that concurrent consideration of RMSE values and correlation coef ficients of SSIs and residuals could effectively forecast the arm’s orientation. The measurements were done in a rather simple rural area with few objects, modelling the effects and errors linked to various arm orientations in this kind of area holds promise for enhancing position estimation, both in the same kind of area and as well in more complex areas like cities with numerous reflective objects causing multipath effects or signal blockage
- PostEvaluation of high rate real time GPS based tsunami warning system(2009) Sundström, Jonas; Chalmers tekniska högskola / Institutionen för radio- och rymdvetenskap; Chalmers University of Technology / Department of Radio and Space ScienceJet Propulsion Laboratory (JPL) is transmitting real time stream of GPS measurement over Internet via a UDP socket. It is a high rate stream that sends 1 Hz data from several stations, today the total number is 70 – 80 stations. This thesis is focusing on finding problems not only with the stream itself, also current problems with the actual measurement. There will be some improvement described however no focus is in network setup or geodetic detection of an actual earthquake. The delay of the stream is gradually increasing from 5 to 15 seconds and drops down to 5 seconds again. This delay is end to end time and have a rate of about one to one and a half hour. Over this time period JPL receives data, process it and resend it to end user. At the receiver end not all data arrives. There are 10 missing measurement in a row at the time the delay drops. The statement is that anywhere in the processing, either at JPL or at receiving computer there is a overflow in a buffer which explains the drop. There are other drops of data, which can be from seconds to hours in length. Whenever the dropped station starts to transmit again, sigma tends to be very large, which is a good thing. However it returns very quickly to normal, much faster than the actual GPS position. A sigma can take in the order of minutes to return while positions takes hours. This problem can be misleading and can create further problem for filters or other processing jobs where sigma is used. Different stations seem to be affected by the missing measure differently. This can explain the variation in result of displacement error. The measurement is subject to a centimeter to decimeter displacement error for a ten- minute gap of data. The displacement error is larger when ever a loss of data occurs. During the next coming hours a large variation of the measurement occurs and a displacement error will be much greater. The solution for this is either to minimize any drop of data which can be a matter of investing in better connection for the receiver stations around the world to JPL or look into the models JPL have and give a better sigma estimate. There are a significant autocorrelation in the signal, the peak can be up to 80% of top value and is close to a sidereal day. Because of this continues correlation a filter can be used to improve the time series. A five-day median filter gives an improvement up to 60%. This number will increase whenever the stated problems above are resolved.
- PostEvaluation of sea level sensors at the Onsala space observatory(2015) Wahlbom, Jonas; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesAbstract A rise of the global mean sea level by more than one metre by the year 2100 is expected. Measurements of the local sea level variations are important to understand the effect on a global scale. This report evaluate a new tide gauge installation at the Onsala Space Observatory with the aim to perform measurements at millimetre accuracy. The new tide gauge consist of two types of level sensors placed in a stilling well. A compact bubbler system and a pulsed radar where the compact bubbler system in the experimental setup consists of a total of five units of which two of the units are of a standard version with a nominal accuracy of 5 mm and three of them of an improved version (called USGS) with a nominal accuracy of 3 mm. Several indoor and field experiments were performed to evaluate the sensors in terms of accuracy, linearity, and stability. A new type of bubble chamber was constructed and compared to the original one. Systematic errors were found when the radar was placed in a narrow tube during the indoor experiments and tendencies of the same systematic error was found in the field experiment even though the tube in this case was significantly wider. A standard deviation of 2.5 mm was found in the differences between the USGS versions in the field environment and a standard deviation of 10 mm between the standard bubbler and the USGS version which was about the same standard deviation that was found between the USGS bubblers and the radar. An improvement was seen in the comparison between the standard bubbler unit and the radar were a standard deviation of 6.5 mm was found. The reason for the better agreement between the less accurate bubbler and the radar is believed to be the timing of the sampling units. The radar and standard bubbler uses the same logging unit and are therefore sampled at the same time. The comparison between the bubbler chambers did not result in any significant differences. This evaluation will serve as a valuable foundation to continued measurements and improvements of the new tide gauge.
- PostHigh resolution imaging with SAR using automotive millimeter wave radars(2021) Leander, Oskar; Pettersson, Viktor; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Ulander, Lars; Monteith, Albert; Eriksson, OlofAngular resolution is currently one of the main limitations in automotive radars used in advanced driver assistance systems (ADAS). This thesis investigates the pos sibility of achieving fine-resolution radar images with a commercial, off-the-shelf au tomotive radar sensor using synthetic aperture radar (SAR). Two imaging algorithms have been investigated and implemented with a Texas Instruments AWR1843 radar system, and the resulting resolution in azimuth has been compared to that of conven tional processing methods. The potential of a side-looking SAR imaging system has been investigated in the ory, in simulations and an experimental system was implemented on an actual moving vehicle. Imaging of various automotive scenarios have been performed, and the image quality of the two algorithms, backprojection and Doppler beam sharpening (DBS), has been evaluated. Simulations and measurements show that the resulting system greatly improves azimuth resolution over the conventional multiple-input multiple output (MIMO) imaging capability of the AWR1843 when in a side-looking mode of operation. The results have helped uncover potential challenges with SAR imaging, such as dynamic scenes and imperfect radar platform motion estimation. The latter problem was overcome using autofocus algorithms. In conclusion, the devised SAR system shows great promise in delivering fine az imuthal information for improving situational awareness in future ADAS functionality using today’s hardware.
- PostInformation extraction from spaceborne SAR data of up to 64-image depth image stacks.(2020) Hessing, Adam; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Ulander, Lars; Dammert, Patrik; Smith-Jonforsen, GaryThe spatial statistics of synthetic aperture radar (SAR) images of the Earth’s surface have been extensively studied in the past. Recent commercial projects from several companies will provide a lot of high quality and importantly high quantity of SAR satellite data, which enables the analysis of the SAR images in time (temporal) instead. This thesis has investigated two different image stacks, containing 28 and 64 images respectively, of SAR intensity data. The investigation has focused on how the statistical distributions in time can be characterized. The temporal SAR data have been tested against eight different target distribution models with the Anderson- Darling goodness-of-fit test. The use of the Anderson-Darling test together with looking for spatial patterns have allowed for comparison of how well the target distribution models fit, even with a limited number of images available. Both statistical and visual interpretations of the results have been made through tables and false-colored images. The results have shown that the distribution of temporal SAR intensity data follows a Gamma distribution irrespective of surface area type. Furthermore, none of the target distributions performed specifically well on areas containing buildings and structures. There was a difference how well the Gamma distribution model performed between the smaller and larger image stack, where the Gamma distribution model performed better for the larger stack, which could point to even better fit to the distribution model if an even larger image stack was used.
- PostRay-tracing based atmospheric propagation simulator for a 2x2 LOS MIMO system(2023) Zhou, Yongan; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Eriksson, Patrick; Bao, Lei; Coldrey, MikaelA microwave radio system with multiple antennas is one popular technology for backhaul network deployment to reach the capability increase required for 5G and 6G. Antenna separations at transmit and receive sites should be carefully designed to ensure a proper phase relation, in this Multiple Input Multiple Output (MIMO) system with long Line-of-Sight (LoS) paths between transmitter and receiver. The LOS MIMO system may fail to operate under an extremely refractive atmosphere due to a lack of sufficient system gain which is determined by the power level and phase condition of the received sub-streams. The contribution of the thesis is to provide a simulator that can model radio’s at mospheric propagation, and it can be further used to verify real link measurement data. It is tested that the simulator has minor accuracy loss over the propagating distance concerned in this study. The simulation of electromagnetic wave propa gation is based on Forward Ray Tracing (FRT). The results demonstrate that the simulator is capable of predicting channel performance (MIMO gain, MIMO phase, etc.) for a 2-by-2 LOS MIMO system over a refractive atmosphere. The results also demonstrate that the simulator is found to be in good agreement with the lit erature and with Parabolic Equation (PE) methods, validating its potential use for predicting the outage probability for the MIMO link. This study, to the author’s best knowledge, is the first work that models the im pact of atmospheric refractivity on LOS MIMO channels using FRT. It is found that for a 2x2 LOS MIMO system the antenna separation calculated assuming free space propagation is also valid for the case of standard refractivity. For other re fraction conditions, the link will more likely experience an outage due to variation in phase condition than loss of power. In addition, atmospheric multipath may in duce random MIMO phase variation. However, the simulator cannot yet properly tackle surface-induced effects on the signals; this requires further development of the software.
- PostSpaceborne signals of opportunity for reflectometry and scatterometry(2020) Isaksson, Frans-Erik; Bennet, Patrik; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Haas, Rüdiger; Christensen, JacobThis master’s thesis is carried out in two main parts. The first part is a compilation of literature studies of the general passive reflectometry and scatterometry principles, techniques, capabilities and needs. The second part, motivated by arguing the results of the previous, consists of an implemented agriculture soil moisture PAssive Reflectometry and Interferometry System (PARIS) experiment using Ku-band TV Direct Broadcasting Satellite (TV-DBS) opportunity signals. It includes the definition of the experiment setup as well as the derivation of a system model indicating the expected performance. It also covers the process of designing, implementing and verifying the PARIS RF hardware front-end and signal processing software, generating the Delay-Doppler Map (DDM) measurement results. The experiment was performed at the World Heritage Grimeton Radio Station where the PARIS was installed at 120 meters height in an antenna tower overlooking the surrounding agriculture. The results show that the Ku-band TV-DBS PARIS is able to clearly detect the signal at all four measurement areas investigated, even when that differs from the expected region of specular reflection. The measurements Signal-to-Noise Ratio (SNR) varies in between about 10 to 24 dB, while the system model expect it to be exponentially distributed around 18.5 dB. The signal scattering is concluded to consist of both significant specular and diffuse parts, possibly allowing for simultaneous measurements of the the whole system antenna beam coverage area independent of the direction of observation. Future prospects of a Ku-band TV-DBS soil moisture PARIS is extrapolated from the experiment results and discussed, with focus put on three thought products - a stationary installation overlooking agriculture, a dronecarried monitoring system as well as a Low-Earth Orbit (LEO) small satellite Earth Observation (EO) constellation.