http://localhost:8081/jspui/handle/123456789/29 2025-07-11T22:48:51Z 2025-07-11T22:48:51Z Kumar, Ajeet http://localhost:8081/jspui/handle/123456789/16477 2025-05-28T13:56:48Z 2019-07-01T00:00:00Z

Title: ANALYSES OF HYBRID-POLSAR DATA FOR LANDCOVER CLASSIFICATION Authors: Kumar, Ajeet Abstract: The knowledge of landcover or landuse becomes increasingly important to overcome the problems related to uncontrolled urban development and depletion of valuable wetlands, agriculture lands, and forest, etc. Landcover resources are directly utilized by humans and subsequently the change in landcover directly affects the lives of human beings. For better use of the land, the information about the existing landcover patterns and the changes in landcover through time are of prime concern. Hence, landcover monitoring through the classification of landcover types has become popular among the researchers working related to earth observatory applications. To perform the landcover classification, spaceborne and airborne Synthetic Aperture Radar (SAR) systems are found to be very efficient due to its day-and-night and all-weather monitoring capabilities. Especially, the SAR system adorned with full-polarimetric (full-pol) configuration have provided promising results in past three decades. The full-pol SAR systems transmit two orthogonal polarizations in one time slot and coherently receive dual orthogonal polarizations. The information acquired by full-pol system allows to generate the full-pol scattering matrix which leads to complete-polarimetric-scattering information about the target. However, the full-pol SAR systems suffer from certain limitations. Transmission of two pulses in one time slot reduces the round-trip delay of backscattered echo by a factor of two, to avoid range ambiguities. Consequently, the swath coverage area of full-pol system is halved, which in turn has adverse impact on the revisit time. This makes full-pol systems not preferable for the applications requiring frequent Earth observation. The full-pol systems also have disadvantages related to high transmitted power requirement and increased data volume per pixel. To overcome these disadvantages of full-pol SAR systems, dual-pol SAR is being utilized. There are two types of dual-pol configurations, i.e. coherent and non-coherent, reported in literature. Between these two, the coherent type of dual-pol (compact-pol) SAR systems are preferred because it retains the relative phase difference between the two received channels to fully characterize the backscattered field. Based on the different combination of transmitted and received polarizations, three different compact-pol configurations, namely p/4, Dual-Circular-Pol (DCP), and hybrid-pol are established in literature. The p/4 mode transmits 45 oriented linear wave and coherently receives two orthogonal linear H and V polarizations, whereas, the DCP mode transmits right/left hand circular polarization and coherently receives right and left hand circular polarizations. The hybrid-pol mode is a combination of circular and linear polarizations, which transmits right/left hand circular polarization and coherently receives two orthogonal linear H and V polarizations. Further among these three compact-pol modes, the hybrid-pol is established as an optimum choice, due to having simple architecture, in-dependency on the oriented target structures, and negligible co- and cross-polarization interference. Initially, the hybrid-pol based satellites, such as Mini-SAR on India’s lunar Chandraayan-1 and Mini-RF on NASA’s Lunar Reconnaissance Orbiter were launched for the application of planetary exploration. Moreover, for Earth-observing purposes, most of the major space agencies have either launched their own hybrid-pol based satellite, or are actively indulged in establishing a new one to launch in near future. For example, Radar Imaging Satellite-1 (RISAT-1) by ISRO and Advanced Land Observation Satellite-2 (ALOS-2) by JAXA are launched in April 2012 and May 2014, respectively. Further, RADARSAT Constellation Mission (RCM) by Canadian Space Agency, SAOCOM-1 by CONAE, and NISAR jointly by NASA-ISRO, are planned to be launched in the near future. However, for the analysis of hybrid-pol data, there had been quite a few approaches reported in the open literature and further establishment of new methods is popular among the researchers. The work presented in this thesis adds on to the current research and provides four new analytical methods. These proposed methods have better performance than the conventional as well as state-of-the-art reported methods.

2019-07-01T00:00:00Z Sharma, Rakesh http://localhost:8081/jspui/handle/123456789/15544 2023-06-23T12:56:52Z 2019-10-01T00:00:00Z

Title: ANALYSES OF DESPECKLING ALGORITHMS FOR POLARIMETRIC SAR DATA Authors: Sharma, Rakesh Abstract: Polarimetric SAR (PolSAR) systems can characterize different land features based on decomposition parameters. The estimation of these parameters is often biased due to the presence of speckle noise. Speckle noise in PolSAR returns depicts a peculiar signal-dependent phenomenon and is better characterized by a multiplicative model rather than an additive one. Also, as the noise statistics are far from Gaussian, specialized tools for PolSAR speckle filtering different from the standard image denoising tools are required. PolSAR data is necessarily characterized by the polarimetric/ scattering information and its spatial resolution. So, in the process of speckle filtering, these features of the PolSAR data should be significantly preserved. Indeed, this is the main motivation behind the work carried out in this thesis. Accordingly, this thesis is divided into two main areas of the study. The first part concerns about development and analyses of speckle filters for full-pol SAR data. And the second part deals with the development and analysis of speckle filter for hybrid-pol SAR data. In this process, four novel PolSAR speckle filters are developed and presented that apart from reducing noise, preserve the polarimetric information as well as the spatial resolution of the data. First, the l1-NLM filter that performs better than conventional non-local patch-based PolSAR filter in excessive noise is presented. l1- NLM filter is implemented by the famousWeiszfeld’s algorithm to find the weighted l1-norm distance minimization estimate. Second, the CFAR-PolSAR filter that integrates Wishart based pre-classification to PolSAR speckle filtering is demonstrated. CFAR-PolSAR filter achieves extended noise reduction and edge preservation with lesser computations. Third, a texture classification based filter (TCBF) is presented that exploits the differences between texture variations and speckle heterogeneity in the PolSAR data. The speckle noise generates a heterogeneity pattern in PolSAR data that is distinct from textural variations due to heterogeneous media. Also, the K-distribution similarity of covariance matrices is derived. Fourth, a speckle filtering approach named as Stokes based sigma filter (SBSF) based on probability density function of Stokes parameters is presented. Also, a new sigma range calculation algorithm depending on degree of polarization and mean intensities is presented. In order to illustrate the relevance of above PolSAR speckle filters, the experiix Abstract ments are conducted over variety of PolSAR datasets. In this work, two full-pol single-look RADARSAT-2 datasets acquired over Mumbai (India) coastal area and San Fransisco (USA) bay area are used. A four-look full-pol AIRSAR dataset acquired over San Fransisco (USA) bay area is also used. Analysis of the efficacy of SBSF on real hybrid-pol SAR data is demonstrated on single-look hybrid-pol RISAT-1 data acquired over Mumbai city (India). Apart from these real PolSAR datasets, simulated datasets are generated through Monte Carlo simulation approach and analyzed for evaluation of the filtering performance. In summary, this thesis contributes in the development of PolSAR speckle filters that: 1) preserve scattering information, textural information, and data statistics, 2) enhance averaging in homogeneous regions, 3) filter heterogeneous regions with preservation of sharp details and edges, 4) un-filter strong targets, and 5) reduce computational complexity.

2019-10-01T00:00:00Z Verma, Upendra Kumar http://localhost:8081/jspui/handle/123456789/15542 2023-06-23T12:58:25Z 2019-07-01T00:00:00Z

Title: INTERFACIAL CHARGE TRANSFER PROCESSES IN QUANTUM DOT SOLAR CELLS Authors: Verma, Upendra Kumar Abstract: Quantum dots (QDs) are extensively used in photovoltaic devices due to their unique properties: bandgap tunability, capability of multiple exciton generation, up/down wavelength conversion. The improvement in device performance is attributed to the enhancement in optical absorption, quantum efficiency, and reduction in thermalization losses. Good optical, as well as electrical properties of the QDs, are essential for efficient device operation. Charge transport and carrier recombination in the QDs are the key processes that affect the device performance and these processes can be easily tuned during the synthesis of QDs and fabrication of the device. In this work, current-voltage characteristics in bilayer heterojunction diodes are studied (effects of energy barriers, layer thicknesses, etc.) and separated into three working regimes based on the energy band diagram of the device. Subsequently, a model for multilayer quantum dot organic solar cells has been developed that explores the impact of electronic processes (carrier recombination, tunneling, injection, etc.) in QDs on the current-voltage (J-V) characteristic of the solar cells. Solar cell characteristics can be controlled by the quantum dot layers. The bimolecular recombination coefficient of QDs is a prime factor that controls the open-circuit voltage without any significant reduction in short circuit current. To verify our proposed model, various core-shell QDs have been fabricated and its interlayer is inserted between the donor and acceptor layer in the device. The addition of QDs has improved the optical absorption in the device resulting in an increase in photo-current/short circuit current density and open-circuit voltage of the solar cell but the current-voltage characteristics show an s-shaped curve in the fourth quadrant which results in drastically reduced fill factor. The reason behind the appearance of s-kink in experimentally obtained J-V characteristic of QD solar cells has been analyzed with the model. According to the model, the capture/emission time and tunneling rate coefficient in QDs are individually responsible for degradation in device performance via an undesirable s-shaped J-V characteristic of hybrid organic/inorganic quantum dot solar cells. Thus, injection/extraction rate, tunneling among QDs and recombination in QDs are essential factors that are required to be optimized for efficient QD solar cells. The structural and energetic disorders at various interfaces, surface properties of QDs, fabrication process, etc. must be taken into consideration to achieve an efficient device.

2019-07-01T00:00:00Z Aravind, Kulkarni Anant http://localhost:8081/jspui/handle/123456789/15541 2023-06-23T13:00:36Z 2019-08-01T00:00:00Z

Title: SPINTRONICS BASED QUANTUM COMPUTING ARCHITECTURES Authors: Aravind, Kulkarni Anant Abstract: A quantum computer performs computations on the principles of quantum mechanics that enables faster speed and higher security than classical computers, and also has the ability to process large amount of information due to its inherent ability of parallel processing. The important building blocks of the quantum computer are qubit, quantum register, quantum logic, quantum network, quantum reversibility, quantum teleportation, quantum data compression, quantum cryptography, universal quantum computing, and quantum algorithm. Quantum computers rely on basic quantum principles of superposition and entanglement. The time evolution of an arbitrary quantum state is computationally more powerful than evolution of a digital logic state. Theoretical quantum computing based on the rotation of the qubits has proved that there is a possibility of quantum devices to address the complex computing problems. However, presently, there is no computer in existence that can completely work on the principles of quantum mechanics. Therefore, the enormous advantages of quantum computing in comparison to its classical counterpart have forced researchers to explore the possibilities of physical realization with the help of emerging technologies. The basic requirements of Divincenzo criteria have to be fulfilled for the successful implementation of the quantum computing. This criteria suggest that the system realizing the quantum computing should have well characterized qubit; proper initial state of all qubits; enough isolation to the qubit(s); precise qubit state manipulation and facilitation of qubits interaction should be in time less than the qubit decoherence time; and the physical system should facilitate the measurement of each qubit to obtain the output of the quantum computation. Spintronics is one of the most efficient ways to physically realize quantum computing due to strong analogy of electron spin to the qubit. Spin-torque based on-chip qubit architecture paves the way for the research in spintronics based physical realization of quantum computer. However, the qubit decoherence is a critical issue in spin qubit architecture from the complex computing point of view. This issue can be dealt by two ways in this thesis; firstly, by utilizing the materials with spin qubits having very high spin coherence, and secondly, by reducing and optimizing the number of elementary quantum operations with the help of elementary quantum gate ii library. This thesis presents both ways in detail with demonstrations of reduction in number of elementary operations by elementary quantum gate library. A computing platform is realized using reduced elementary gates such as CNOT, SWAP, Toffoli, and Fredkin wherein the reduction in number of elementary operations is 36.36%, 36.36%, 35.44%, 35.64%, respectively. The optimization of the reduced number of operations for the quantum circuits representing the Boolean logics AND, OR, XOR, Hall Adder (HA), and Full Adder (FA), is also achieved with a reduction after optimization of 37.97%, 41.58%, 45.45%, 40%, and 40.55%, respectively. A quantum Fourier transform that is an integral part of the Shor's algorithm for the number factorization is also reduced and optimized. The reduction of 35.71% in number of elementary operations for the quantum Fourier transform is also demonstrated. Various other complex computing operations can be realized using the spin torque based qubit architecture. This thesis lays strong foundation for researchers aspiring to work in the area of quantum computing using spintronics platform and also discusses the associated challenges.

2019-08-01T00:00:00Z