Noise removal from multi-channel digital images based on statistical depth functions

U ovoj doktorskoj disertaciji biće predstavljen novi metod za uklanjanje šuma iz višekanalnih digitalnih slika zasnovan na funkcijama statisitičke dubine, preciznije izmenjenoj verziji DEEEPLOC algoritma predstavljenog u radu A. Struyf i P.J. Rousseeuw (Comp. Stat. & Data Analysis 34, 415-426 (2000)) za izračunavanje približne vrednosti poluprostorne (Tukey-eve) najdublje lokacije (medijane) u višedimenzionalnom slučaju. Zbog svoje inherentne višedimenzionalne prirode, predstavljeni metod eliminiše šum istovremeno na svim kanalima slike bez njihovog razdvajanja, čime održava spektralnu korelaciju između kanala u višekanalnoj slici. Rezultati otklanjanja šuma primenom predstavljenog filtera prostornog domena na standardnim slikama za testiranje pokazuju bolje performanse ovog filtera u odnosu na trenutno najpriznatije i najviše korišćene filtere za otklanjanje impulsnih i mešovitih šumova u višekanalnim slikama u smislu objektivnih kriterijuma efektivnosti (odnosa vršnih vrednosti signala i šuma (PSNR), srednje apsolutne greške (MAE) i normalizovanih udaljenosti boja (NCD)), kao i vizuelnog kvaliteta. Predstavljeni filter uspešno održava ivice i fine detalje na slikama, i veoma je efektivan za otklanjanje srednjih i jakih višekanalnih šumova...In this doctoral dissertation a novel method is proposed for removing noise from multi-channel digital images based on statistical depth functions, or more precisely an adapted version of the DEEPLOC algorithm introduced by A. Struyf and P.J. Rousseeuw (Comp. Stat. & Data Analysis 34, 415-426 (2000)) for calculation of approximate halfspace (Tukey’s) deepest location (median) in multivariate case. Due to its intrinsic multivariate/multidimensional nature, the proposed method eliminates the noise simultaneously on all channels without their separation, which preserves the spectral correlation between channels in a multi-channel image. Denoising results of this new non-linear spatial domain filter applied to benchmark images outperform currently used state-of-the-art filters for impulse and mixed noise removal from multi-channel images in terms of both objective effectiveness criteria (peak-signal-to-noise-ratio (PSNR), mean absolute error (MAE) and normalised colour distance (NCD)) and visual quality. Proposed filter successfully preserves the edges and fine image details, and is very effective for removal of medium and heavy multi-channel noise..

Electrical Resistivity Imaging for Unknown Bridge Foundation Depth Determination

Unknown bridge foundations pose a significant safety risk due to stream scour and erosion. Records from older structures may be non-existent, incomplete, or incorrect. Nondestructive and inexpensive geophysical methods have been identified as suitable to investigate unknown bridge foundations. The objective of the present study is to apply advanced 2D electrical resistivity imaging (ERI) in order to identify depth of unknown bridge foundations. A survey procedure is carried out in mixed terrain water and land environments with rough topography. A conventional resistivity survey procedure is used with the electrodes installed on the stream banks. However, some electrodes must be adapted for underwater use. Tests were conducted in one laboratory experimentation and at five field experimentations located at three roadway bridges, a geotechnical test site, and a railway bridge. The first experimentation was at the bridges with the smallest foundations, later working up in size to larger drilled shafts and spread footings. Both known to unknown foundations were investigated. The geotechnical test site is used as an experimental site for 2D and 3D ERI. The data acquisition is carried out along 2D profile with a linear array in the dipole-dipole configuration. The data collections have been carried out using electrodes deployed directly across smaller foundations. Electrodes are deployed in proximity to larger foundations to image them from the side. The 2D ERI can detect the presence of a bridge foundation but is unable to resolve its precise shape and depth. Increasing the spatial extent of the foundation permits better image of its shape and depth. Using electrode < 1 m to detect a slender foundation < 1 m in diameter is not feasible. The 2D ERI method that has been widely used for land surface surveys presently can be adapted effectively in water-covered environments. The method is the most appropriate geophysical method for determination of unknown bridge foundations. Fully 3D ERI method at bridge sites is labor intensive, time consuming, and does not add enough value over 2D ERI to make it worthwhile

Joint interpretations of geophysical measurements as the key to understand landscape evolution

Užitá geofyzika představuje rychlý, efektivní a nedestruktivní způsob získávání informací o složení a stavu horninového prostředí, jakož i o studovaných geologických či geomorfologických procesech. Kombinování různých metod geofyzikálního průzkumu přináší ve srovnání s použitím pouze jedné geofyzikální metody výrazně širší rozsah měřených fyzikálních parametrů, což umožňuje získání mnohem podrobnějších informací o zkoumaném geologickém prostředí. K interpretacím geofyzikálních dat je vždy potřeba přistupovat obezřetně, protože jde mnohdy jen o jedno z pravděpodobných, nikoli však jediných možných řešení. Předkládaná disertační práce na několika vybraných případech ilustruje, jak snadno může dojít k nepřesné, nebo dokonce mylné interpretaci. V řadě případů přitom nemusí jít o problém kvality dat nebo chybného nastavení parametrů výpočetního modelu. Problém nastává při interpretaci výsledků, kdy dochází k přiřazení určité geologické kvality ke konkrétní měřené nebo modelované hodnotě nebo pozorované anomálii. Sdružené interpretace geofyzikálních metod (ideálně doplněné informacemi "negeofyzikálního" charakteru) mohou nejen přinést zásadní informace o studovaných geologických či geomorfologických fenoménech, ale také přispět metodickými poznatky, a to jak k metodám jednotlivým, tak zejména k jejich...Užitá geofyzika představuje rychlý, efektivní a nedestruktivní způsob získávání informací o složení a stavu horninového prostředí, jakož i o studovaných geologických či geomorfologických procesech. Kombinování různých metod geofyzikálního průzkumu přináší ve srovnání s použitím pouze jedné geofyzikální metody výrazně širší rozsah měřených fyzikálních parametrů, což umožňuje získání mnohem podrobnějších informací o zkoumaném geologickém prostředí. K interpretacím geofyzikálních dat je vždy potřeba přistupovat obezřetně, protože jde mnohdy jen o jedno z pravděpodobných, nikoli však jediných možných řešení. Předkládaná disertační práce na několika vybraných případech ilustruje, jak snadno může dojít k nepřesné, nebo dokonce mylné interpretaci. V řadě případů přitom nemusí jít o problém kvality dat nebo chybného nastavení parametrů výpočetního modelu. Problém nastává při interpretaci výsledků, kdy dochází k přiřazení určité geologické kvality ke konkrétní měřené nebo modelované hodnotě nebo pozorované anomálii. Sdružené interpretace geofyzikálních metod (ideálně doplněné informacemi "negeofyzikálního" charakteru) mohou nejen přinést zásadní informace o studovaných geologických či geomorfologických fenoménech, ale také přispět metodickými poznatky, a to jak k metodám jednotlivým, tak zejména k jejich...Ústav hydrogeologie, inženýrské geologie a užité geofyzikyInstitute of Hydrogeology, Engineering Geology and Applied GeophysicsPřírodovědecká fakultaFaculty of Scienc

Uncertainties in the Estimation of the Shear-Wave Velocity and the Small-Strain Damping Ratio from Surface Wave Analysis

L'abstract è presente nell'allegato / the abstract is in the attachmen

Water-borne geophysics for Murray River salt-load detection

Thesis (M.Sc.) -- University of Adelaide, Dept. of Geology and Geophysics, 200

Hydrogeophysical investigation of water recharge into the Gnangara Mound

Increased demand for freshwater in combination with a drying climate has led to water table decline on the Gnangara Groundwater Mound north of Perth, Western Australia. For sustainable groundwater management, a regional-scale modelling system has been developed. Accurate groundwater modelling requires good estimates of aquifer recharge, which in the case of the Superficial Aquifer may be achieved by a Vertical Flux Model. Recharge studies provide this model with input parameters such as unsaturated hydraulic conductivity, soil moisture content and water retention potential. Another key component of sustainable water resource management is to understand the biophysical processes that are involved in surface- and groundwater and plant interaction in order to conserve the natural ecosystem.Hydrogeophysical measurements have the potential to provide non-invasive, in-situ physical parameter estimation for the near-surface. As such it provides a tool to quantify and monitor unsaturated zone dynamics. From hydrogeophysical observations, hydrogeologic parameters can be deduced and then used as constraints for the numerical modelling. Geophysical monitoring further provides field evidence to corroborate or reject modelling results. Some subsurface physical properties are invariable over long time-scales (e.g. depositional features, porosity) and can be mapped with geophysical measurements. Other subsurface components are subject to temporal variations. They are determined by environmental factors, for example the water content changes during the hydrogeologic cycle. Capturing those seasonal variations requires time lapse investigation..The groundwater recharge rates at the Gnangara Mound are dominated by winter rainfall in a Mediterranean climate setting. Rainwater infiltrates through a sandy soil profile that contains water retentive soil horizons. In this thesis, the physical properties of the soil and their temporal variations are explored using Ground-Penetrating Radar (GPR) and neutron logging to delineate the influence of water retentive soil horizons.The spatial distribution of indurated, friably cemented sand layers varies spatially. To delineate these layers, large-scale surface 2D common offset GPR reflection profiles that span the entire groundwater mound are examined. It is found that these layers produce strong reflections in the radargrams that suggest a strong contrast in water content; indicating water retentiveness is present. An analysis scheme is developed that allows large-scale classification of water retention potential based on spatial reflector configuration and reflection strength. The results from spatial investigation indicate that the distribution of potentially water retentive layers is patchy. Where pronounced layers exist, they commonly show dip, which in combination with pipe structures (dissolution and root channels) is likely to result in preferential flow.Laboratory dielectric experiments on samples with variable water saturation demonstrate that retentive and non-retentive soil horizons have a similar dielectric permittivity versus water content relationship which corroborates that high reflectivity indicates elevated water content.Six test sites were selected for time lapse investigation based on soil properties and hydrogeologic setting. A range of surveys were performed before, during and after the annual rainfall cycle in 2011 to capture the temporal variability of vertical water content distribution. Time-lapse crosswell- and surface-to-hole borehole radar datasets were acquired. To obtain high certainty moisture content profiles from those data, a new processing scheme is proposed based on a combined use of zero-offset profiling and vertical radar profiling. Sequential and baseline difference curves are calculated and reveal infiltration scenarios ranging from simple wetting and unsaturated flow regime, to delayed wetting and impeded flow. While some impact on infiltration can be attributed to retentive soil layers, it was found that vegetation appears to play a crucial role in determining soil moisture depletion between wetting cycles. The results from the time-lapse GPR were validated by analysis of long-term time-lapse neutron logging. Neutron logging reinforces the view that retention horizons are unlikely to store additional plant available water compared to the clean sand intervals.Very near-surface water content measurements are a challenge with commercial common offset GPR systems. I develop a new analysis methodology that enables estimation of water content as part of the spatial and temporal characterization of shallow moisture distribution. Dispersion curves are derived from shallow diffracted wavefields that appear in common offset GPR due to a waveguide structure. Inversion based on modal wave propagation in a waveguide allows derivation of waveguide parameters. Dispersion curves are demonstrated to be sensitive to small changes in waveguide properties, which are strongly dependent upon water content. Field examples illustrate the full potential of this technique in lateral near-surface water content quantification.The small- and large scale surveys presented in this thesis form the basis for examination and advancement of the radar methodology in a sandy environment as well as providing field evidence for hydrogeologic significance and distribution of water retentive soil horizons in the unsaturated zone of the Swan Coastal Plain, Western Australia