Search

Your search keyword '"Yardim, Caglar"' showing total 123 results
Start Over Author "Yardim, Caglar" Search Limiters Available in Library Collection
123 results on '"Yardim, Caglar"'

1. CASPER : Coupled Air–Sea Processes and Electromagnetic Ducting Research

Author

Wang, Qing, Alappattu, Denny P., Billingsley, Stephanie, Blomquist, Byron, Burkholder, Robert J., Christman, Adam J., Creegan, Edward D., de Paolo, Tony, Eleuterio, Daniel P., Fernando, Harindra Joseph S., Franklin, Kyle B., Grachev, Andrey A., Haack, Tracy, Hanley, Thomas R., Hocut, Christopher M., Holt, Teddy R., Horgan, Kate, Jonsson, Haflidi H., Hale, Robert A., Kalogiros, John A., Khelif, Djamal, Leo, Laura S., Lind, Richard J., Lozovatsky, Iossif, Planella-Morato, Jesus, Mukherjee, Swagato, Nuss, Wendell A., Pozderac, Jonathan, Rogers, L. Ted, Savelyev, Ivan, Savidge, Dana K., Shearman, R. Kipp, Shen, Lian, Terrill, Eric, Ulate, A. Marcela, Wang, Qi, Wendt, R. Travis, Wiss, Russell, Woods, Roy K., Xu, Luyao, Yamaguchi, Ryan T., and Yardim, Caglar

Published
2018

2. Statistical maritime radar duct estimation using hybrid genetic algorithm-Markov chain Monte Carlo method

Author

Yardim, Caglar, Gerstoft, Peter, and Hodgkiss, William S.

Abstract

[1] This paper addresses the problem of estimating the lower atmospheric refractivity ( M profile) under nonstandard propagation conditions frequently encountered in low-altitude maritime radar applications. This is done by statistically estimating the duct strength (range- and height-dependent atmospheric index of refraction) from the sea surface reflected radar clutter. These environmental statistics can then be used to predict the radar performance. In previous work, genetic algorithms (GA) and Markov chain Monte Carlo (MCMC) samplers were used to calculate the atmospheric refractivity from returned radar clutter. Although GA is fast and estimates the maximum a posteriori ( MAP) solution well, it poorly calculates the multidimensional integrals required to obtain the means, variances, and underlying posterior probability distribution functions of the estimated parameters. More accurate distributions and integral calculations can be obtained using MCMC samplers, such as the Metropolis-Hastings and Gibbs sampling (GS) algorithms. Their drawback is that they require a large number of samples relative to the global optimization techniques such as GA and become impractical with an increasing number of unknowns. A hybrid GA-MCMC method based on the nearest neighborhood algorithm is implemented in this paper. It is an improved GA method which improves integral calculation accuracy through hybridization with a MCMC sampler. Since the number of forward models is determined by GA, it requires fewer forward model samples than a MCMC, enabling inversion of atmospheric models with a larger number of unknowns.

Published
2007

3. Ice Sheet and Sea Ice Ultrawideband Microwave radiometric Airborne eXperiment (ISSIUMAX) in Antarctica: first results from Terra Nova Bay

Author

Brogioni, Marco, primary, Andrews, Mark J., additional, Urbini, Stefano, additional, Jezek, Kenneth C., additional, Johnson, Joel T., additional, Leduc-Leballeur, Marion, additional, Macelloni, Giovanni, additional, Ackley, Stephen F., additional, Bringer, Alexandra, additional, Brucker, Ludovic, additional, Demir, Oguz, additional, Fontanelli, Giacomo, additional, Yardim, Caglar, additional, Kaleschke, Lars, additional, Montomoli, Francesco, additional, Tsang, Leung, additional, Becagli, Silvia, additional, and Frezzotti, Massimo, additional

Published
2023
Full Text
View/download PDF

12. Tracking refractivity from clutter using Kalman and particle filters

Author

Yardim, Caglar, Gerstoft, Peter, and Hodgkiss, William S.

Subjects
Tracking systems -- Research, Algorithms -- Methods, Kalman filtering -- Methods, Refractive index -- Properties, Fourier transformations -- Properties, Algorithm, Business, Computers, Electronics, Electronics and electrical industries
Abstract

We address the problem of tracking the spatial and temporal lower atmospheric variations in maritime environments. The evolution of the range and height-dependent index of refraction is tracked using the sea clutter return from sea-borne radars operating in the region. A split-step fast Fourier transform based parabolic equation approximation to the wave equation is used to compute the clutter return in complex environments with varying index of refraction. In addition, regional statistics are incorporated as prior densities, resulting in a highly nonlinear and non-Gaussian tracking problem. Tracking algorithms such as the extended Kalman, unscented Kalman and particle filters are used for tracking both evaporative and surface-based electromagnetic ducts frequently encountered in marine environments. The tracking performances and applicability of these techniques to different types of refractivity-from-clutter problems are studied using the posterior Cramer-Rao lower bound. Track divergence statistics are analyzed. The results show that while the tracking performance of the Kalman filters is comparable to the particle filters in evaporative duct tracking, it is limited by the high non-linearity of the parabolic equation for the surface-based duct case. Particle filters, on the other hand, prove to be very promising in tracking a wide range of environments including the abruptly changing ones. Index Terms--Atmospheric ducts, extended Kalman filter (EKF), parabolic equation, particle filter (PF), refractivity-fromclutter (RFC), spatial and temporal tracking, unscented Kalman filter (UKF).

Published
2008

13. Estimation of radio refractivity from radar clutter using Bayesian Monte Carlo analysis

Author

Yardim, Caglar, Gerstoft, Peter, and Hodgkiss, William S.

Subjects
Bayesian statistical decision theory -- Analysis, Genetic algorithms -- Analysis, Monte Carlo method -- Analysis, Radio waves -- Analysis, Business, Computers, Electronics, Electronics and electrical industries
Abstract

This paper describes a Markov chain Monte Carlo (MCMC) sampling approach for the estimation of not only the radio refractivity profiles from radar clutter but also the uncertainties in these estimates. This is done by treating the refractivity from clutter (RFC) problem in a Bayesian framework. It uses unbiased MCMC sampling techniques, such as Metropolis and Gibbs sampling algorithms, to gather more accurate information about the uncertainties. Application of these sampling techniques using an electromagnetic split-step fast Fourier transform parabolic equation propagation model within a Bayesian inversion framework can provide accurate posterior probability distributions of the estimated refractivity parameters. Then these distributions can be used to estimate the uncertainties in the parameters of interest. Two different MCMC samplers (Metropolis and Gibbs) are analyzed and the results compared not only with the exhaustive search results but also with the genetic algorithm results and helicopter refractivity profile measurements. Although it is slower than global optimizers, the probability densities obtained by this method are closer to the true distributions. Index Terms--Atmospheric ducts, genetic algorithms, Markov chain Monte Carlo (MCMC) techniques, radar clutter, refractivity estimation.

Published
2006

14. Microwave Radiometry at Frequencies From 500 to 1400 MHz: An Emerging Technology for Earth Observations

Author

Johnson, Joel T., primary, Jezek, Kenneth C., additional, Macelloni, Giovanni, additional, Brogioni, Marco, additional, Tsang, Leung, additional, Dinnat, Emmanuel P., additional, Walker, Jeffrey P., additional, Ye, Nan, additional, Misra, Sidharth, additional, Piepmeier, Jeffrey R., additional, Bindlish, Rajat, additional, LeVine, David M., additional, OaNeill, Peggy E., additional, Kaleschke, Lars, additional, Andrews, Mark J., additional, Yardim, Caglar, additional, Aksoy, Mustafa, additional, Durand, Michael, additional, Chen, Chi-Chih, additional, Demir, Oguz, additional, Bringer, Alexandra, additional, Miller, Julie Z., additional, Brown, Shannon T., additional, Kwok, Ron, additional, Lee, Tong, additional, Kerr, Yann, additional, Entekhabi, Dara, additional, Peng, Jinzheng, additional, Colliander, Andreas, additional, Chan, Steven, additional, MacGregor, Joseph A., additional, Medley, Brooke, additional, DeRoo, Roger, additional, and Drinkwater, Mark, additional

Published
2021
Full Text
View/download PDF

16. Statistical estimation and tracking of refractivity from radar clutter

Author

Yardim, Caglar

Abstract

In many maritime regions of the world, such as the Mediterranean, Persian Gulf, East China Sea, and the Californian Coast, atmospheric ducts are common occurrences. They result in various anomalies such as significant variations in the maximum operational radar range, creation of regions where the radar is practically blind (radar holes) and increased sea clutter. Therefore, it is important to predict the real-time 3-D environment in which the radar is operating so that the radar operator will at least know the true system limitations and in some cases even compensate for them. This dissertation addresses the estimation and tracking of the lower atmospheric radio refractivity under non-standard propagation conditions frequently encountered in low altitude maritime radar applications. This is done by statistically estimating the duct strength (range and height-dependent atmospheric index of refraction) from the sea-surface reflected radar clutter. Therefore, such methods are called Refractivity From Clutter (RFC) techniques. These environmental statistics can then be used to predict the radar performance. The electromagnetic propagation in these complex environments is simulated using a split-step fast Fourier transform (FFT) based parabolic equation (PE) approximation to the wave equation. The first part of this thesis discusses various algorithms such as genetic algorithms (GA), Markov chain Monte Carlo samplers (MCMC) and the hybrid GA-MCMC samplers that are used to estimate atmospheric radio refractivity for a given azimuth direction and time. The results show that radar clutter can be a rich source of information about the environment and the techniques mentioned above are used successfully as near real-time estimators for the data collected during the Wallops'98 experiment conducted by the Naval Surface Warfare Center. The second part of this dissertation focuses on both spatial and temporal tracking of the 3-D environment. Techniques such as the extended (EKF) and unscented (UKF) Kalman filters, and particle filters (PF) are used for tracking the spatial and temporal evolution of the lower atmosphere. Even though the tracking performance of the Kalman filters was limited for certain duct types such as the surface-based ducts due to the high non-linearity of the split-step FFT PE, they performed well for other environments such as evaporation ducts. On the other hand, particle filters proved to be very promising in tracking a wide variety of scenarios including even abruptly changing environments

Published
2007

19. 500–2000-MHz Brightness Temperature Spectra of the Northwestern Greenland Ice Sheet

Author

Jezek, Kenneth C., primary, Johnson, Joel T., additional, Tan, Shurun, additional, Tsang, Leung, additional, Andrews, Mark J., additional, Brogioni, Marco, additional, Macelloni, Giovanni, additional, Durand, Michael, additional, Chen, Chi-Chih, additional, Belgiovane, Domenic J., additional, Duan, Yuna, additional, Yardim, Caglar, additional, Li, Hongkun, additional, Bringer, Alexandra, additional, Leuski, Vladimir, additional, and Aksoy, Mustafa, additional

Published
2018
Full Text
View/download PDF

20. CASPER: Coupled Air-Sea Processes and Electromagnetic Ducting Research

Author

Naval Postgraduate School (U.S.), Meteorology, Wang, Qing, Alappattu, Denny P., Billingsley, Stephanie, Blomquist, Byron, Burkholder, Robert J., Christman, Adam J., Creegan, Edward D., Paolo, Tony De, Eleuterio, Daniel P., Fernando, Harindra Joseph S., Franklin, Kyle B., Grachev, Andrey A., Haack, Tracy, Hanley, Thomas R., Hocut, Christopher M., Holt, Teddy R., Horgan, Kate, Jonsson, Haflidi H., Hale, Robert A., Kalogiros, John A., Khelif, Djamal, Leo, Laura S., Lind, Richard J., Lozovatsky, Iossif, Planella-Morato, Jesus, Mukherjee, Swagato, Nuss, Wendell A., Pozderac, Jonathan, Rogers, L. Ted, Savelyev, Ivan, Savidge, Dana K., Shearman, R. Kipp, Shen, Lian, Terrill, Eric, Ulate, A. Marcela, Wang, Qi, Wendt, R. Travis, Wiss, Russell, Woods, Roy K., Xu, Luyao, Yamaguchi, Ryan T., Yardim, Caglar, Naval Postgraduate School (U.S.), Meteorology, Wang, Qing, Alappattu, Denny P., Billingsley, Stephanie, Blomquist, Byron, Burkholder, Robert J., Christman, Adam J., Creegan, Edward D., Paolo, Tony De, Eleuterio, Daniel P., Fernando, Harindra Joseph S., Franklin, Kyle B., Grachev, Andrey A., Haack, Tracy, Hanley, Thomas R., Hocut, Christopher M., Holt, Teddy R., Horgan, Kate, Jonsson, Haflidi H., Hale, Robert A., Kalogiros, John A., Khelif, Djamal, Leo, Laura S., Lind, Richard J., Lozovatsky, Iossif, Planella-Morato, Jesus, Mukherjee, Swagato, Nuss, Wendell A., Pozderac, Jonathan, Rogers, L. Ted, Savelyev, Ivan, Savidge, Dana K., Shearman, R. Kipp, Shen, Lian, Terrill, Eric, Ulate, A. Marcela, Wang, Qi, Wendt, R. Travis, Wiss, Russell, Woods, Roy K., Xu, Luyao, Yamaguchi, Ryan T., and Yardim, Caglar

Abstract

The objective of CASPER is to improve our capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air–sea interaction processes, refractive environment, and RF propagation.

Published
2017

23. Sequential Geoacoustic Filtering and Geoacoustic Inversion

Author

SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Hodgkiss, Bill, Yardim, Caglar, Menon, Ravi, SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Hodgkiss, Bill, Yardim, Caglar, and Menon, Ravi

Abstract

The development of new geoacoustic inversion methods, their use in the analysis of shallow water experimental data, and evaluation of geoacoustic model and parameter uncertainties including the mapping of these uncertainties through to system performance uncertainties.

Published
2014

26. Sequential Geoacoustic Filtering and Utilizing Ambient Noise for Geoacoustic Inversion

Author

SCRIPPS INST OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, Menon, Ravi, Hodgkiss, Bill, SCRIPPS INST OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, Menon, Ravi, and Hodgkiss, Bill

Abstract

The development of new geoacoustic inversion methods, their use in the analysis of shallow water experimental data, and evaluation of geoacoustic model and parameter uncertainties including the mapping of these uncertainties through to system performance uncertainties. Analysis of geoacoustic inversion data collected from various experiments. Of specific technical interest are: (1) development of methods to track the environmental parameters using sequential filtering, (2) use of ambient noise for estimation of seafloor structure parameters, and (3) the development of new inversion methods for use into the kHz frequency regime. In an ONR Graduate Traineeship Awards we address using Random Matrix Theory in ocean acoustics.

Published
2013

27. Trident Warrior 2013 Opportunistic VHF and UHF Observations

Author

SPACE AND NAVAL WARFARE SYSTEMS CENTER PACIFIC SAN DIEGO CA, Rogers, Ted, Lynch, Stephen, Fuhrer, Nathan, Yardim, Caglar, SPACE AND NAVAL WARFARE SYSTEMS CENTER PACIFIC SAN DIEGO CA, Rogers, Ted, Lynch, Stephen, Fuhrer, Nathan, and Yardim, Caglar

Abstract

Utilize signals from emitters of opportunity to (a) evaluate sources of propagation predictions (e.g., numerical weather prediction), and (b) provide real-time refractivity information using EM inverse methods.

Published
2013

28. Refractivity Data Fusion

Author

SPACE AND NAVAL WARFARE SYSTEMS CENTER PACIFIC SAN DIEGO CA, Rogers, Ted, Gerstoft, Peter, Yardim, Caglar, SPACE AND NAVAL WARFARE SYSTEMS CENTER PACIFIC SAN DIEGO CA, Rogers, Ted, Gerstoft, Peter, and Yardim, Caglar

Abstract

Long-term Goals: Fuse refractivity inferred from electromagnetic (EM) propagation observations with background fields from numerical weather prediction (NWP) models. Objectives: Develop data fusion method for atmospheric refractivity scheme based on objective analysis. Develop means to map observations of refractivity based on RF propagation measurements into the space utilized for the analysis. Exercise the data fusion scheme on a combination of synthetic and real data to assess performance. Achieve reasonable processing time (on the order of 1-minute) with a representative domain size using a high-end laptop computer., Prepared in collaboration with University of California, San Diego, CA.

Published
2013

30. Sequential Geoacoustic Filtering and Utilizing Ambient Noise for Geoacoustic Inversion

Author

SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, Menon, Ravi, Hodgkiss, Bill, SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, Menon, Ravi, and Hodgkiss, Bill

Abstract

The development of new geoacoustic inversion methods, their use in the analysis of shallow water experimental data, and evaluation of geoacoustic model and parameter uncertainties including the mapping of these uncertainties through to system performance uncertainties. Analysis of geoacoustic inversion data collected from various experiments. Of specific technical interest are: (1) development of methods to track the environmental parameters using sequential filtering, (2) use of ambient noise for estimation of seafloor structure parameters, and (3) the development of new inversion methods for use into the kHz frequency regime. In an ONR Graduate Traineeship Awards we address using Random Matrix Theory in ocean acoustics., The original document contains color images.

Published
2012

31. Sequential Geoacoustic Filtering and Utilizing Ambient Noise for Geoacoustic Inversion

Author

SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, Hodgkiss, Bill, SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB, Gerstoft, Peter, Yardim, Caglar, and Hodgkiss, Bill

Abstract

The development of new geoacoustic inversion methods, their use in the analysis of shallow water experimental data, and evaluation of geoacoustic model and parameter uncertainties including the mapping of these uncertainties through to system performance uncertainties. Analysis of geoacoustic inversion data collected from various experiments. Of specific technical interest are: (1) development of methods to track the environmental parameters using sequential filtering, (2) use of ambient noise for estimation of seafloor structure parameters, and (3) the development of new inversion methods for use into the kHz frequency regime.

Published
2011

32. Optimizing Refractivity from Clutter (RFC) for Surface-Based Ducts

Author

SPACE AND NAVAL WARFARE SYSTEMS COMMAND SAN DIEGO CA, Barrios, Amalia E, Fuhrer, Nathan, Gerstoft, Peter, Yardim, Caglar, Karimian, Ali, SPACE AND NAVAL WARFARE SYSTEMS COMMAND SAN DIEGO CA, Barrios, Amalia E, Fuhrer, Nathan, Gerstoft, Peter, Yardim, Caglar, and Karimian, Ali

Abstract

Develop electromagnetic propagation models, and refractivity inversion algorithms, that perform equally well over land and sea and in the presence of anomalous propagation conditions for both surface and airborne emitters, for use in operational or engineering propagation assessment systems.

Published
2011

33. Optimizing Refractivity from Clutter (RFC) for Surface-Based Ducts

Author

SPACE AND NAVAL WARFARE SYSTEMS CENTER SAN DIEGO CA ATMOSPHERIC PROPAGATION BRANCH, Barrios, Amalia E., Fuhrer, Nathan, Gerstoft, Peter, Yardim, Caglar, Karimian, Ali, SPACE AND NAVAL WARFARE SYSTEMS CENTER SAN DIEGO CA ATMOSPHERIC PROPAGATION BRANCH, Barrios, Amalia E., Fuhrer, Nathan, Gerstoft, Peter, Yardim, Caglar, and Karimian, Ali

Abstract

Develop electromagnetic propagation models, and refractivity inversion algorithms, that perform equally well over land and sea and in the presence of anomalous propagation conditions for both surface and airborne emitters, for use in operational or engineering propagation assessment systems. Develop an advanced unified hybrid radio propagation model based on parabolic equation and rayoptics methods for both surface-based and airborne applications. This model is named the Advanced Propagation Model (APM) and is the primary model used in the Advanced Refractive Effects Prediction System (AREPS). The specific technical objectives are to develop algorithms to extract surface clutter only from weather files provided by the Hazardous Weather Detection and Display Capability (HWDDC); and to improve, refine, and optimize the current state-of-the-art Refractivity From Clutter (RFC) algorithms to infer and characterize surface-based ducts (SBD)., Prepared in collaboration with Scripps Institute of Oceanography, San Diego, CA.

Published
2010

Catalog

Books, media, physical & digital resources
See catalog results