Zaib Khan - Academia.edu (original) (raw)

Papers by Zaib Khan

Research paper thumbnail of Coupled hydrogeophysical inversion of time-lapse off-ground GPR and hydrological data

We present a coupled hydrogeophysical inversion approach that uses time-lapse off-ground ground-p... more We present a coupled hydrogeophysical inversion approach that uses time-lapse off-ground ground-penetrating radar (GPR) data and other hydrological data for estimating soil hydraulic parameters, and apply it to data sets collected in a field experiment. Off-ground GPR data are mainly related to the near-surface water content profile and time variations thereof, and are thus only indirectly related to soil hydraulic parameters, such as the permeability and the parameters of the relative permeability and capillary pressure functions. However, in our approach the GPR model is coupled to a hydrodynamic model, such that the electromagnetic parameters (dielectric constant and electrical conductivity) that serve as input to the GPR model become a function of hydrodynamic model output (i.e., water content), thereby enabling estimation of the soil hydraulic properties with GPR data (together with other data sets) in an inverse modelling framework (iTOUGH2). The hydrodynamic model used in this work is based on a one-dimensional solution of non-isothermal multiphase flow. The GPR model involves a full-waveform frequency-domain solution of Maxwell's equations for wave propagation in three-dimensional multilayered media. The data sets we consider were collected in a field experiment at the Selhausen test site of Forschungszentrum Juelich, Germany, in summer 2009 over a 30-day period in which three major precipitation events occurred. To monitor the dynamics of the soil, time-lapse TDR, temperature, and GPR measurements were performed repeatedly. The probes used for the TDR and temperature measurements were installed at four depths near the footprint of the GPR antennae. Preliminary results suggest that improved estimates of soil hydraulic parameters are obtained when both GPR and hydrological measurements are used for inversion, compared to using either data set alone.

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Research paper thumbnail of 5Amino1-phenyl-1 H -pyrazole-4-carboxylic acid

Acta Crystallographica Section E-structure Reports Online, 2008

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Research paper thumbnail of Investigation of the frequency dependent antenna transfer functions and phase center position for modeling off-ground GPR

We compared different methods to estimate the phase center of an ultra wideband ground penetratin... more We compared different methods to estimate the phase center of an ultra wideband ground penetrating radar (GPR) horn antenna operating off-ground, namely, (1) extrapolation of peak-to-peak reflection values in the time domain and assuming a fixed phase center, and (2), frequency-domain full-waveform inversion assuming a frequency dependent phase center. For that purpose, we performed radar measurements at different heights above a perfect electrical conductor (PEC). A double ridged horn antenna operating in the frequency range 0.8-5.2 GHz was used. In the limits of the antenna geometry, we observed that antenna modeling results were not significantly affected by the position of the phase center, even when considering frequency dependence. This implies that the transfer function model used to model the antenna inherently accounts for the phase center position. This analysis showed that the proposed antenna model avoids the need for the frequency dependent phase center determination and is valid for any applications where the field measured by the antenna can be considered as coming from a distance larger than the antenna aperture itself, such as for off-ground GPR or telecommunications.

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Research paper thumbnail of Analysis of Horn Antenna Transfer Functions and Phase-Center Position for Modeling Off-Ground GPR

IEEE Transactions on Geoscience and Remote Sensing, 2011

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Research paper thumbnail of Ground-penetrating radar characterization of water as a function of frequency, salinity and temperature

We conducted a laboratory experiment to test the ground penetrating radar (GPR) full-waveform for... more We conducted a laboratory experiment to test the ground penetrating radar (GPR) full-waveform forward and inverse modeling approach for electromagnetic wave propagation in water. The GPR system consisted of a vector network analyzer combined with an air-launched, 0.8-2.2 GHz horn antenna, thereby setting up an ultra wideband stepped-frequency continuous-wave radar. The apparent frequency-, salinity-, and temperature-dependent dielectric permittivity and electrical conductivity of water were estimated by using existing electrical models. Using these models, the radar data could be simulated and a remarkable agreement was obtained with the laboratory measurements. Neglecting the frequency-, salinity-, and temperature-effects led to less satisfactory results, especially regarding signal amplitude. Inversion of the radar data permitted to reconstruct the air and water layer thicknesses, and to some extent, the water electrical properties. This analysis particularly showed the benefit of using proper water electrical models compared to commonly used simplified approaches in GPR forward and inverse modeling.

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Research paper thumbnail of Full-Waveform Modelling and Inversion of Ground-Penetrating Radar Data for Non-invasive Characterisation of Soil Hydrogeophysical Properties

We present a new technique for real-time, proximal sensing of the soil hydrogeophysical propertie... more We present a new technique for real-time, proximal sensing of the soil hydrogeophysical properties using ground-penetrating radar (GPR). The radar system is based on international standard vector network analyser technology, thereby setting up stepped-frequency continuous-wave GPR. The radar is combined with an off-ground, ultra-wideband, and highly directional horn antenna acting simultaneously as transmitter and receiver. Full-waveform forward modelling of the radar signal includes antenna propagation phenomena through a system of linear transfer functions in series and parallel. The system takes into account antenna–soil interactions and assumes the air–subsurface compartments as a three-dimensional multilayered medium, for which Maxwell’s equations are solved exactly. We provide an efficient way for estimating the spatial Green’s function as a solution of Maxwell’s equations from its spectral counterpart by deforming the integration path in the complex plane of the integration variable. Signal inversion is formulated as a complex least squares problem and is solved iteratively using the global multilevel coordinate search optimisation algorithm combined with the local Nelder–Mead simplex method. The electromagnetic model has unprecedented accuracy for describing the GPR signal in controlled laboratory conditions, providing accurate estimates for both soil dielectric permittivity and electrical conductivity. The proposed method has been specifically designed for the retrieval of soil surface dielectric permittivity and correlated surface water content, which has been validated in field conditions. We also show that constraining the electromagnetic inverse problem using hydrodynamic modelling theoretically permits retrieval of the soil hydraulic properties and reconstruction of continuous vertical water content profiles from time-lapse GPR data. The proposed method shows great promise for field-scale, high-resolution digital soil mapping, and thereby for bridging the spatial-scale gap between ground truthing based on soil sampling or local probes and airborne and spaceborne remote sensing.

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Research paper thumbnail of Remotely Estimation of the Soil Hydraulic Properties by Using Full-Waveform Hydrogeophysical Inversion of the Time-Lapse GPR Data

Recently, ground-penetrating radar (GPR) is increasingly being used to provide quantitative infor... more Recently, ground-penetrating radar (GPR) is increasingly being used to provide quantitative information of the subsurface distributions and hydrological properties. We used integrated hydrogeophysical inversion of time-lapse, proximal ground penetrating radar (GPR) data to remotely estimate the unsaturated soil hydraulic properties. The radar system is based on international standard vector network analyzer technology and a full-waveform model is used to describe wave propagation in the antenna-air-soil system, including antenna-soil interactions. Hydrodynamic modeling was based on a one-dimensional solution of Richard’s equation and was used to constrain the inverse electromagnetic problem in reconstructing vertical water content profiles. As a result, the estimated parameters reduce to the soil hydraulic properties, thereby strongly reducing the dimensionality of the inverse problem. The approach is tested in controlled laboratory conditions for a variable infiltration event in a homogeneous sandy soil. In total, sixteen GPR observations were made with uneven time steps, to catch most of the observed water dynamics. Results were compared with TDR and ground truth measurements. Finally, we tested the approach in real field conditions at one location. TDR probes were installed at four different depths to infer the dynamics of vertical water content profile and used as a reference method for comparsion. The results suggest that the proposed method is promising for characterizing the shallow subsurface hydraulic properties at the field scale with a high spatial resolution.

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Research paper thumbnail of Mapping Field-Scale Soil Moisture With L-Band Radiometer and Ground-Penetrating Radar Over Bare Soil

IEEE Transactions on Geoscience and Remote Sensing, 2011

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Research paper thumbnail of Self-optimizing resource management in High Throughput Computing Systems

... Pakistan 2Department of Computer Science Lahore University of Management Sciences Lahore – Pa... more ... Pakistan 2Department of Computer Science Lahore University of Management Sciences Lahore – Pakistan e-mail :{zaibimran2006, anam.tahir.29}@gmail.com1, sizzbee@hotmail. com1, jahan@lums.edu.pk2 ... techniques. Javed, F. et. al. ...

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Research paper thumbnail of Salinity–sodicity induced changes in reproductive physiology of rice ( Oryza sativa) under dense soil conditions

Environmental and Experimental Botany, 2003

Seed set in rice under salinity stress is a major problem caused by a number of factors. The most... more Seed set in rice under salinity stress is a major problem caused by a number of factors. The most important factor which is not explored yet in rice under field conditions is stigma receptivity and grain filling against salinity–sodicity stress. We conducted experiments to study the effect ...

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Research paper thumbnail of EFFECTS OF ENVIRONMENT ON PROGESTERONE LEVEL OF DAIRY CATTLE IN DISTRICT NOWSHERA

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Research paper thumbnail of Coupled hydrogeophysical inversion of time-lapse off-ground GPR and hydrological data

We present a coupled hydrogeophysical inversion approach that uses time-lapse off-ground ground-p... more We present a coupled hydrogeophysical inversion approach that uses time-lapse off-ground ground-penetrating radar (GPR) data and other hydrological data for estimating soil hydraulic parameters, and apply it to data sets collected in a field experiment. Off-ground GPR data are mainly related to the near-surface water content profile and time variations thereof, and are thus only indirectly related to soil hydraulic parameters, such as the permeability and the parameters of the relative permeability and capillary pressure functions. However, in our approach the GPR model is coupled to a hydrodynamic model, such that the electromagnetic parameters (dielectric constant and electrical conductivity) that serve as input to the GPR model become a function of hydrodynamic model output (i.e., water content), thereby enabling estimation of the soil hydraulic properties with GPR data (together with other data sets) in an inverse modelling framework (iTOUGH2). The hydrodynamic model used in this work is based on a one-dimensional solution of non-isothermal multiphase flow. The GPR model involves a full-waveform frequency-domain solution of Maxwell's equations for wave propagation in three-dimensional multilayered media. The data sets we consider were collected in a field experiment at the Selhausen test site of Forschungszentrum Juelich, Germany, in summer 2009 over a 30-day period in which three major precipitation events occurred. To monitor the dynamics of the soil, time-lapse TDR, temperature, and GPR measurements were performed repeatedly. The probes used for the TDR and temperature measurements were installed at four depths near the footprint of the GPR antennae. Preliminary results suggest that improved estimates of soil hydraulic parameters are obtained when both GPR and hydrological measurements are used for inversion, compared to using either data set alone.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 5Amino1-phenyl-1 H -pyrazole-4-carboxylic acid

Acta Crystallographica Section E-structure Reports Online, 2008

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Research paper thumbnail of Investigation of the frequency dependent antenna transfer functions and phase center position for modeling off-ground GPR

We compared different methods to estimate the phase center of an ultra wideband ground penetratin... more We compared different methods to estimate the phase center of an ultra wideband ground penetrating radar (GPR) horn antenna operating off-ground, namely, (1) extrapolation of peak-to-peak reflection values in the time domain and assuming a fixed phase center, and (2), frequency-domain full-waveform inversion assuming a frequency dependent phase center. For that purpose, we performed radar measurements at different heights above a perfect electrical conductor (PEC). A double ridged horn antenna operating in the frequency range 0.8-5.2 GHz was used. In the limits of the antenna geometry, we observed that antenna modeling results were not significantly affected by the position of the phase center, even when considering frequency dependence. This implies that the transfer function model used to model the antenna inherently accounts for the phase center position. This analysis showed that the proposed antenna model avoids the need for the frequency dependent phase center determination and is valid for any applications where the field measured by the antenna can be considered as coming from a distance larger than the antenna aperture itself, such as for off-ground GPR or telecommunications.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Analysis of Horn Antenna Transfer Functions and Phase-Center Position for Modeling Off-Ground GPR

IEEE Transactions on Geoscience and Remote Sensing, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Ground-penetrating radar characterization of water as a function of frequency, salinity and temperature

We conducted a laboratory experiment to test the ground penetrating radar (GPR) full-waveform for... more We conducted a laboratory experiment to test the ground penetrating radar (GPR) full-waveform forward and inverse modeling approach for electromagnetic wave propagation in water. The GPR system consisted of a vector network analyzer combined with an air-launched, 0.8-2.2 GHz horn antenna, thereby setting up an ultra wideband stepped-frequency continuous-wave radar. The apparent frequency-, salinity-, and temperature-dependent dielectric permittivity and electrical conductivity of water were estimated by using existing electrical models. Using these models, the radar data could be simulated and a remarkable agreement was obtained with the laboratory measurements. Neglecting the frequency-, salinity-, and temperature-effects led to less satisfactory results, especially regarding signal amplitude. Inversion of the radar data permitted to reconstruct the air and water layer thicknesses, and to some extent, the water electrical properties. This analysis particularly showed the benefit of using proper water electrical models compared to commonly used simplified approaches in GPR forward and inverse modeling.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Full-Waveform Modelling and Inversion of Ground-Penetrating Radar Data for Non-invasive Characterisation of Soil Hydrogeophysical Properties

We present a new technique for real-time, proximal sensing of the soil hydrogeophysical propertie... more We present a new technique for real-time, proximal sensing of the soil hydrogeophysical properties using ground-penetrating radar (GPR). The radar system is based on international standard vector network analyser technology, thereby setting up stepped-frequency continuous-wave GPR. The radar is combined with an off-ground, ultra-wideband, and highly directional horn antenna acting simultaneously as transmitter and receiver. Full-waveform forward modelling of the radar signal includes antenna propagation phenomena through a system of linear transfer functions in series and parallel. The system takes into account antenna–soil interactions and assumes the air–subsurface compartments as a three-dimensional multilayered medium, for which Maxwell’s equations are solved exactly. We provide an efficient way for estimating the spatial Green’s function as a solution of Maxwell’s equations from its spectral counterpart by deforming the integration path in the complex plane of the integration variable. Signal inversion is formulated as a complex least squares problem and is solved iteratively using the global multilevel coordinate search optimisation algorithm combined with the local Nelder–Mead simplex method. The electromagnetic model has unprecedented accuracy for describing the GPR signal in controlled laboratory conditions, providing accurate estimates for both soil dielectric permittivity and electrical conductivity. The proposed method has been specifically designed for the retrieval of soil surface dielectric permittivity and correlated surface water content, which has been validated in field conditions. We also show that constraining the electromagnetic inverse problem using hydrodynamic modelling theoretically permits retrieval of the soil hydraulic properties and reconstruction of continuous vertical water content profiles from time-lapse GPR data. The proposed method shows great promise for field-scale, high-resolution digital soil mapping, and thereby for bridging the spatial-scale gap between ground truthing based on soil sampling or local probes and airborne and spaceborne remote sensing.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Remotely Estimation of the Soil Hydraulic Properties by Using Full-Waveform Hydrogeophysical Inversion of the Time-Lapse GPR Data

Recently, ground-penetrating radar (GPR) is increasingly being used to provide quantitative infor... more Recently, ground-penetrating radar (GPR) is increasingly being used to provide quantitative information of the subsurface distributions and hydrological properties. We used integrated hydrogeophysical inversion of time-lapse, proximal ground penetrating radar (GPR) data to remotely estimate the unsaturated soil hydraulic properties. The radar system is based on international standard vector network analyzer technology and a full-waveform model is used to describe wave propagation in the antenna-air-soil system, including antenna-soil interactions. Hydrodynamic modeling was based on a one-dimensional solution of Richard’s equation and was used to constrain the inverse electromagnetic problem in reconstructing vertical water content profiles. As a result, the estimated parameters reduce to the soil hydraulic properties, thereby strongly reducing the dimensionality of the inverse problem. The approach is tested in controlled laboratory conditions for a variable infiltration event in a homogeneous sandy soil. In total, sixteen GPR observations were made with uneven time steps, to catch most of the observed water dynamics. Results were compared with TDR and ground truth measurements. Finally, we tested the approach in real field conditions at one location. TDR probes were installed at four different depths to infer the dynamics of vertical water content profile and used as a reference method for comparsion. The results suggest that the proposed method is promising for characterizing the shallow subsurface hydraulic properties at the field scale with a high spatial resolution.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mapping Field-Scale Soil Moisture With L-Band Radiometer and Ground-Penetrating Radar Over Bare Soil

IEEE Transactions on Geoscience and Remote Sensing, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Self-optimizing resource management in High Throughput Computing Systems

... Pakistan 2Department of Computer Science Lahore University of Management Sciences Lahore – Pa... more ... Pakistan 2Department of Computer Science Lahore University of Management Sciences Lahore – Pakistan e-mail :{zaibimran2006, anam.tahir.29}@gmail.com1, sizzbee@hotmail. com1, jahan@lums.edu.pk2 ... techniques. Javed, F. et. al. ...

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Research paper thumbnail of Salinity–sodicity induced changes in reproductive physiology of rice ( Oryza sativa) under dense soil conditions

Environmental and Experimental Botany, 2003

Seed set in rice under salinity stress is a major problem caused by a number of factors. The most... more Seed set in rice under salinity stress is a major problem caused by a number of factors. The most important factor which is not explored yet in rice under field conditions is stigma receptivity and grain filling against salinity–sodicity stress. We conducted experiments to study the effect ...

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Research paper thumbnail of EFFECTS OF ENVIRONMENT ON PROGESTERONE LEVEL OF DAIRY CATTLE IN DISTRICT NOWSHERA

Bookmarks Related papers MentionsView impact