Cuneyt Utku - Academia.edu (original) (raw)

Papers by Cuneyt Utku

Fırat University Turkish journal of science & technology, Mar 20, 2022

Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is ... more Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is investigated. A theoretical framework is provided based on Multiple Signal Classification (MUSIC) imaging, formerly developed for timereversal imaging of point-like targets in cluttered environment. Numerical simulations are provided to assist in understanding the relations between various aspects of the imaging method. Numerical evidence shows that for the same signal to noise ratio, higher order harmonics (second and third harmonics) resulting from nonlinear scattering, have better imaging resolutions compared to the fundamental harmonic corresponding to linear scattering.

Turkish Journal of Science and Technology, 2022

Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is ... more Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is investigated. A theoretical framework is provided based on Multiple Signal Classification (MUSIC) imaging, formerly developed for time-reversal imaging of point-like targets in cluttered environment. Numerical simulations are provided to assist in understanding the relations between various aspects of the imaging method. Numerical evidence shows that for the same signal to noise ratio, higher order harmonics (second and third harmonics) resulting from nonlinear scattering, have better imaging resolutions compared to the fundamental harmonic corresponding to linear scattering.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477)

... Roger H. Lang and Cuneyt Utku George Washington University Washington, DC 20052, USA lang@sea... more ... Roger H. Lang and Cuneyt Utku George Washington University Washington, DC 20052, USA lang@seas.gwu.edu ... The solid line is from Klein and Swift [4] and the dashed line is from the recent measurements of S. Blanch and A. Aguasca at the Polytechnic University of ...

2014 13th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2014

A numerical reconstruction of the brightness temperature is examined as a potential way to improv... more A numerical reconstruction of the brightness temperature is examined as a potential way to improve the retrieval of salinity from Aquarius measurements closer to land-water boundaries. A test case using simulated ocean-land scenes suggest promise for the technique.

Current retrieval algorithms for microwave remote sensing of soil moisture, generally assume a tw... more Current retrieval algorithms for microwave remote sensing of soil moisture, generally assume a two-dimensional geometry (horizontal plane) possibly with small scale roughness appropriate for agriculture. However, for accurate retrievals of soil moisture on a global scale, the impact of earth’s topography on the sensor output needs to be investigated. In this paper, an analytical study of the impact of topography on antenna temperature is presented using Digital Elevation Maps (DEM) for the site of the Soil Moisture Experiment (SMEX04). The results predict a large impact for rough terrain at large incidence angles.

IEEE Transactions on Geoscience and Remote Sensing, 2021

A new microwave (MW) imaging technique for the reconstruction of complex permittivity profiles of... more A new microwave (MW) imaging technique for the reconstruction of complex permittivity profiles of lossy dielectric objects is proposed. The proposed technique is based on partial coherence in thermal radiation of objects and is distinct from interferometric radiometry used for high-resolution imaging of brightness temperature. This is a unique feature of the method that distinguishes it from other MW imaging methods for permittivity reconstruction, where the underlying physical phenomenon is electromagnetic scattering by the probed object. Equations governing the imaging method are presented, and its potential for complex permittivity reconstruction in two dimensions is demonstrated with simulations.

Radio Science, 2016

This report describes measurements of the dielectric constant of seawater at a frequency of 1.413... more This report describes measurements of the dielectric constant of seawater at a frequency of 1.413 GHz that is at the center of the L-Sand radiometric protected frequency spectrum. Aquarius will be sensing the sea surface salinity from space in this band. The objective of the project is to refine the model function for the dielectric constant as a function of salinity and temperature so that remote sensing measurements can be made with the accuracy needed to meet the measurement goals (0.2 psu) of the Aquarius mission. The measurements were made, using a microwave cavity operated in the transmission configuration. The cavity's temperature was accurately regulated to 0.02 C by immersing it in a temperature controlled bath of distilled water and ethanol glycol. Seawater had been purchased from Ocean Scientific International Limited (OS1L) at salinities of 30, 35 and 38 psu. Measurements of these seawater samples were then made over a range of temperatures, from l0 C to 35 C in 5 C intervals. Repeated measurements were made at each temperature and salinity, Mean values and standard deviations were then computed. Total error budgets indicated that the real and imaginary parts of the dielectric constant had a relative accuracy of about l%.

This paper describes a resonant cavity technique for the measurement of the dielectric constant o... more This paper describes a resonant cavity technique for the measurement of the dielectric constant of seawater as a function of its salinity. Accurate relationships between salinity and dielectric constant (which determines emissivity) are needed for sensor systems such as SMOS and Aquarius that will monitor salinity from space in the near future. The purpose of the new measurements is to establish the dependence of the dielectric constant of seawater on salinity in contemporary units (e.g. psu) and to take advantage of modern instrumentation to increase the accuracy of these measurements. The measurement device is a brass cylindrical cavity 16cm in diameter and 7cm in height. The seawater is introduced into the cavity through a slender glass tube having an inner diameter of 0.1 mm. By assuming that this small amount of seawater slightly perturbs the internal fields in the cavity, perturbation theory can be employed. A simple formula results relating the real part of the dielectric constant to the change in resonant frequency of the cavity. In a similar manner, the imaginary part of the dielectric constant is related to the change in the cavity s Q. The expected accuracy of the cavity technique is better than 1% for the real part and 1 to 2% for the imaginary part. Presently, measurements of methanol have been made and agree with precision measurements in the literature to within 1% in both real and imaginary parts. Measurements have been made of the dielectric constant of seawater samples from Ocean Scientific in the United Kingdom with salinities of 10, 30, 35 and 38 psu. All measurements were made at room temperature. Plans to make measurements at a range of temperatures and salinities will be discussed.

2009 3rd European Conference on Antennas and Propagation, 2009

Multiple scattering effects in a two-dimensional forest of tree trunks whose radii are small or l... more Multiple scattering effects in a two-dimensional forest of tree trunks whose radii are small or large with respect to the wavelength is studied. The radiative transport equation is used to solve for the specific intensity in the forest medium. Using the circular symmetry of the trunk and assuming that the transmitter and the receiver are in the same transverse plane, the radiative transport equation is solved numerically by the eigenvalue technique. The solution is used to compute both the coherent and the incoherent attenuation constants in the trunk-dominated forest. In the low frequency limit the results are compared with the values obtained from a Monte-Carlo simulation of an ensemble of infinite length vertical cylinders.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Global monitoring of sea surface salinity from space requires an accurate model for the dielectri... more Global monitoring of sea surface salinity from space requires an accurate model for the dielectric constant of sea water as a function of salinity and temperature to characterize the emissivity of the surface. Measurements are being made at 1.413 GHz, the center frequency of the Aquarius radiometers, using a resonant cavity and the perturbation method. The cavity is operated in a transmission mode and immersed in a liquid bath to control temperature. Multiple measurements are made at each temperature and salinity. Error budgets indicate a relative accuracy for both real and imaginary parts of the dielectric constant of about 1%.

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

Measurements of the complex. dielectric constant of seawater at 30.00 psu, 35.00 psu and 38.27 ps... more Measurements of the complex. dielectric constant of seawater at 30.00 psu, 35.00 psu and 38.27 psu over the temperature range from 5°C to 3 5 '~ at 1.413 GHz are given and compared with the Kiein-Swift results. A resonant cavity technique is used. The calibration constant used in the cavity perturbation formulas is determined experimentally using methanol and ethanediol (ethylene gycol) as reference liquids. Analysis of the data shows that the measurements are accurate to better than 1 .O% in almost all cases studied.

2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, 2013

Seawater salinity measurements are currently being made at L-band (1.413 Ghz) by NASA's Aquar... more Seawater salinity measurements are currently being made at L-band (1.413 Ghz) by NASA's Aquarius instrument (on the Aquarius/SAC-D observatory). The goal of Aquarius mission is to measure the salinity of seawater to an accuracy on the order of 0.2 psu; this requires a model function of seawater permittivity with a high accuracy. Since 2011, the George Washington University (GW) has employed a cavity technique to determine the complex permittivity of seawater at 1.413 GHz. In this paper, a new seawater dielectric model function is introduced including the latest permittivity data for seawater with salinity 33 psu. Finally, the validation of the end-effect, measurement variance and data fitting will be discussed.

2012 12th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2012

This paper describes new measurements made in 2011-2012 of the dielectric constant of seawater at... more This paper describes new measurements made in 2011-2012 of the dielectric constant of seawater at 1.413 GHz using a resonant cavity technique. These measurements are more accurate than previous measurements made in 2008. The paper discusses the improved experimental methods used for the 2011-12 measurements. The new measurement data is also be compared with Klein-Swift (KS) model function and Meissner-Wentz (MW) model function.

Conference Proceedings 2000 International Conference on Mathematical Methods in Electromagnetic Theory (Cat. No.00EX413), 2000

ABSTRACT

Geoscience and Remote Sensing IEEE International Symposium, 2004

Relations between various definitions of albedo for a layer of random discrete scatterers are est... more Relations between various definitions of albedo for a layer of random discrete scatterers are established. Albedo and attenuation values are obtained for soybeans and corn using a discrete model. Attenuation values are also obtained using an empirical approach. Brightness temperatures, computed by transport theory with these albedo and attenuation values, are compared with the measured brightness temperature values for soybeans

IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH37217)

Airborne measurements of brightness temperature at L-band over conifer stands located in Southern... more Airborne measurements of brightness temperature at L-band over conifer stands located in Southern Virginia were made in July, August and November of 1999. Ground truth data related to forest stands and ground were also collected. The conifer stands were modeled by the distorted Born approximation (DBA) in conjunction with Peak's principle. The ground was modeled as a half space with surface roughness. The soil permittivity was related to its volumetric moisture through Dobson's model. It was observed that with sufficiently accurate measurement of ground temperature it is possible to see through the forest and retrieve information about the moisture of the underlying soil

Fırat University Turkish journal of science & technology, Mar 20, 2022

Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is ... more Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is investigated. A theoretical framework is provided based on Multiple Signal Classification (MUSIC) imaging, formerly developed for timereversal imaging of point-like targets in cluttered environment. Numerical simulations are provided to assist in understanding the relations between various aspects of the imaging method. Numerical evidence shows that for the same signal to noise ratio, higher order harmonics (second and third harmonics) resulting from nonlinear scattering, have better imaging resolutions compared to the fundamental harmonic corresponding to linear scattering.

Turkish Journal of Science and Technology, 2022

Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is ... more Narrowband localization of point-like nonlinear scatterers in a homogeneous background medium is investigated. A theoretical framework is provided based on Multiple Signal Classification (MUSIC) imaging, formerly developed for time-reversal imaging of point-like targets in cluttered environment. Numerical simulations are provided to assist in understanding the relations between various aspects of the imaging method. Numerical evidence shows that for the same signal to noise ratio, higher order harmonics (second and third harmonics) resulting from nonlinear scattering, have better imaging resolutions compared to the fundamental harmonic corresponding to linear scattering.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477)

... Roger H. Lang and Cuneyt Utku George Washington University Washington, DC 20052, USA lang@sea... more ... Roger H. Lang and Cuneyt Utku George Washington University Washington, DC 20052, USA lang@seas.gwu.edu ... The solid line is from Klein and Swift [4] and the dashed line is from the recent measurements of S. Blanch and A. Aguasca at the Polytechnic University of ...

2014 13th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2014

A numerical reconstruction of the brightness temperature is examined as a potential way to improv... more A numerical reconstruction of the brightness temperature is examined as a potential way to improve the retrieval of salinity from Aquarius measurements closer to land-water boundaries. A test case using simulated ocean-land scenes suggest promise for the technique.

Current retrieval algorithms for microwave remote sensing of soil moisture, generally assume a tw... more Current retrieval algorithms for microwave remote sensing of soil moisture, generally assume a two-dimensional geometry (horizontal plane) possibly with small scale roughness appropriate for agriculture. However, for accurate retrievals of soil moisture on a global scale, the impact of earth’s topography on the sensor output needs to be investigated. In this paper, an analytical study of the impact of topography on antenna temperature is presented using Digital Elevation Maps (DEM) for the site of the Soil Moisture Experiment (SMEX04). The results predict a large impact for rough terrain at large incidence angles.

IEEE Transactions on Geoscience and Remote Sensing, 2021

A new microwave (MW) imaging technique for the reconstruction of complex permittivity profiles of... more A new microwave (MW) imaging technique for the reconstruction of complex permittivity profiles of lossy dielectric objects is proposed. The proposed technique is based on partial coherence in thermal radiation of objects and is distinct from interferometric radiometry used for high-resolution imaging of brightness temperature. This is a unique feature of the method that distinguishes it from other MW imaging methods for permittivity reconstruction, where the underlying physical phenomenon is electromagnetic scattering by the probed object. Equations governing the imaging method are presented, and its potential for complex permittivity reconstruction in two dimensions is demonstrated with simulations.

Radio Science, 2016

This report describes measurements of the dielectric constant of seawater at a frequency of 1.413... more This report describes measurements of the dielectric constant of seawater at a frequency of 1.413 GHz that is at the center of the L-Sand radiometric protected frequency spectrum. Aquarius will be sensing the sea surface salinity from space in this band. The objective of the project is to refine the model function for the dielectric constant as a function of salinity and temperature so that remote sensing measurements can be made with the accuracy needed to meet the measurement goals (0.2 psu) of the Aquarius mission. The measurements were made, using a microwave cavity operated in the transmission configuration. The cavity's temperature was accurately regulated to 0.02 C by immersing it in a temperature controlled bath of distilled water and ethanol glycol. Seawater had been purchased from Ocean Scientific International Limited (OS1L) at salinities of 30, 35 and 38 psu. Measurements of these seawater samples were then made over a range of temperatures, from l0 C to 35 C in 5 C intervals. Repeated measurements were made at each temperature and salinity, Mean values and standard deviations were then computed. Total error budgets indicated that the real and imaginary parts of the dielectric constant had a relative accuracy of about l%.

This paper describes a resonant cavity technique for the measurement of the dielectric constant o... more This paper describes a resonant cavity technique for the measurement of the dielectric constant of seawater as a function of its salinity. Accurate relationships between salinity and dielectric constant (which determines emissivity) are needed for sensor systems such as SMOS and Aquarius that will monitor salinity from space in the near future. The purpose of the new measurements is to establish the dependence of the dielectric constant of seawater on salinity in contemporary units (e.g. psu) and to take advantage of modern instrumentation to increase the accuracy of these measurements. The measurement device is a brass cylindrical cavity 16cm in diameter and 7cm in height. The seawater is introduced into the cavity through a slender glass tube having an inner diameter of 0.1 mm. By assuming that this small amount of seawater slightly perturbs the internal fields in the cavity, perturbation theory can be employed. A simple formula results relating the real part of the dielectric constant to the change in resonant frequency of the cavity. In a similar manner, the imaginary part of the dielectric constant is related to the change in the cavity s Q. The expected accuracy of the cavity technique is better than 1% for the real part and 1 to 2% for the imaginary part. Presently, measurements of methanol have been made and agree with precision measurements in the literature to within 1% in both real and imaginary parts. Measurements have been made of the dielectric constant of seawater samples from Ocean Scientific in the United Kingdom with salinities of 10, 30, 35 and 38 psu. All measurements were made at room temperature. Plans to make measurements at a range of temperatures and salinities will be discussed.

2009 3rd European Conference on Antennas and Propagation, 2009

Multiple scattering effects in a two-dimensional forest of tree trunks whose radii are small or l... more Multiple scattering effects in a two-dimensional forest of tree trunks whose radii are small or large with respect to the wavelength is studied. The radiative transport equation is used to solve for the specific intensity in the forest medium. Using the circular symmetry of the trunk and assuming that the transmitter and the receiver are in the same transverse plane, the radiative transport equation is solved numerically by the eigenvalue technique. The solution is used to compute both the coherent and the incoherent attenuation constants in the trunk-dominated forest. In the low frequency limit the results are compared with the values obtained from a Monte-Carlo simulation of an ensemble of infinite length vertical cylinders.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Global monitoring of sea surface salinity from space requires an accurate model for the dielectri... more Global monitoring of sea surface salinity from space requires an accurate model for the dielectric constant of sea water as a function of salinity and temperature to characterize the emissivity of the surface. Measurements are being made at 1.413 GHz, the center frequency of the Aquarius radiometers, using a resonant cavity and the perturbation method. The cavity is operated in a transmission mode and immersed in a liquid bath to control temperature. Multiple measurements are made at each temperature and salinity. Error budgets indicate a relative accuracy for both real and imaginary parts of the dielectric constant of about 1%.

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

Measurements of the complex. dielectric constant of seawater at 30.00 psu, 35.00 psu and 38.27 ps... more Measurements of the complex. dielectric constant of seawater at 30.00 psu, 35.00 psu and 38.27 psu over the temperature range from 5°C to 3 5 '~ at 1.413 GHz are given and compared with the Kiein-Swift results. A resonant cavity technique is used. The calibration constant used in the cavity perturbation formulas is determined experimentally using methanol and ethanediol (ethylene gycol) as reference liquids. Analysis of the data shows that the measurements are accurate to better than 1 .O% in almost all cases studied.

2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, 2013

Seawater salinity measurements are currently being made at L-band (1.413 Ghz) by NASA's Aquar... more Seawater salinity measurements are currently being made at L-band (1.413 Ghz) by NASA's Aquarius instrument (on the Aquarius/SAC-D observatory). The goal of Aquarius mission is to measure the salinity of seawater to an accuracy on the order of 0.2 psu; this requires a model function of seawater permittivity with a high accuracy. Since 2011, the George Washington University (GW) has employed a cavity technique to determine the complex permittivity of seawater at 1.413 GHz. In this paper, a new seawater dielectric model function is introduced including the latest permittivity data for seawater with salinity 33 psu. Finally, the validation of the end-effect, measurement variance and data fitting will be discussed.

2012 12th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2012

This paper describes new measurements made in 2011-2012 of the dielectric constant of seawater at... more This paper describes new measurements made in 2011-2012 of the dielectric constant of seawater at 1.413 GHz using a resonant cavity technique. These measurements are more accurate than previous measurements made in 2008. The paper discusses the improved experimental methods used for the 2011-12 measurements. The new measurement data is also be compared with Klein-Swift (KS) model function and Meissner-Wentz (MW) model function.

Conference Proceedings 2000 International Conference on Mathematical Methods in Electromagnetic Theory (Cat. No.00EX413), 2000

ABSTRACT

Geoscience and Remote Sensing IEEE International Symposium, 2004

Relations between various definitions of albedo for a layer of random discrete scatterers are est... more Relations between various definitions of albedo for a layer of random discrete scatterers are established. Albedo and attenuation values are obtained for soybeans and corn using a discrete model. Attenuation values are also obtained using an empirical approach. Brightness temperatures, computed by transport theory with these albedo and attenuation values, are compared with the measured brightness temperature values for soybeans

IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH37217)

Airborne measurements of brightness temperature at L-band over conifer stands located in Southern... more Airborne measurements of brightness temperature at L-band over conifer stands located in Southern Virginia were made in July, August and November of 1999. Ground truth data related to forest stands and ground were also collected. The conifer stands were modeled by the distorted Born approximation (DBA) in conjunction with Peak's principle. The ground was modeled as a half space with surface roughness. The soil permittivity was related to its volumetric moisture through Dobson's model. It was observed that with sufficiently accurate measurement of ground temperature it is possible to see through the forest and retrieve information about the moisture of the underlying soil