11 research outputs found

    Future climate analogues of current wheat production zones in India

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    The future of agriculture in India will be affected by substantial changes in the environment, although not uniformly across the country. These changes, as projected by the well-known General Circulation Model will grossly impact the food-cropping system. While developing adaptation strategies, it would be useful to understand the current climatic and farming regimes in similar or analogue sites, which have already experienced future conditions. The data used in this article are from a study using the Climate Analogues tool, a web-based tool developed by the Research Programme on Climate Change, Agriculture and Food Security, which uses spatial and temporal variability in climate projections for different climatic scenarios using the General Circulation Model. Sites with statistically similar climates were thus identified and mapped; these include two sites from four different agroecological regions of wheat cropping in India. Comparisons were made specifically for the year 2030, keeping in mind changes in agricultural techniques and mechanisms that could potentially occur over a span of one and a half decades. Temperature was prioritized over other climatic variables in this study, which was conducted using the ECHAM model for the A2 scenario. A comparison of the current yields of the selected sites with those of the future analogue sites revealed the former to be at low, moderate or high risk, in accordance with the projected future climatic conditions for wheat cultivation. Most sites appeared to be at moderate risk due to temperature increase at these sites by the year 2030, and except for two sites, had significantly reduced yields

    Rethinking climate change: Perception, adaptation and vulnerability among rice and wheat farmers in northern India

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    Climate change is one of the most complex challenges that we face in current times and it will affect human populations across the world. The impacts of climate change are likely to be rather prominent on agricultural systems and on communities dependent on them. My doctoral thesis addressed the subject of climate change from the perspective of rice- and wheat farmers in Uttar Pradesh in northern India, focussing on different vulnerability zones in the state. I examined how traditional knowledge systems and local strategies have been used by farmers to negotiate climatic change that they have experienced. My observations suggest that the understanding of this global phenomenon is rather different at the local level. The thesis thus engaged with specific issues in the different vulnerability zones studied and examined how different groups of farmers in these regions were impacted by and perceived climate change. Rice- and wheat cultivation form the core of agriculture in India and, if affected adversely by changes in climate, could impact our food security. Accordingly, my thesis has discussed farmer understandings of climate change, the problems that they face and their reasons for pursuing short-term coping strategies. My study further assessed the vulnerability of agriculture to climate change and contributes to the larger comparative project of adaptation strategies that may evolve in response to climate change. Vulnerability assessments have typically adopted a top-down approach, especially when formulating state- and national-level economic or policy decisions. Bottom-up approaches of vulnerability assessment, such as participatory methods, however, reveal disparate resources and the existence of locally appropriate strategies even within the same district. Villages experience disparities, ranging from access to resources to varying socio-economic and environmental conditions. Vulnerability is also not simply restricted to change in climatic conditions – certain populations are more vulnerable than others, on the bases of gender, caste or class, thus making climate change itself an axis of marginalisation. My studies conclude by insisting on the development and adoption of interdisciplinary, culturally sensitive, multi-scalar approaches to further understand the vulnerability of agricultural communities to climate change, strategies adopted to combat it and the barriers to such adaptability in rural northern India

    Investigation of accurate fringe analysis techniques for fringe projection profilometry

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    Optical 3D measurement techniques have been studied and developed for a long time in literature now due to its non-contact, high speed, high accuracy, and sensitivity, for 3D measurements. Fringe pattern analysis (FPA) is an important aspect of all optical measurement techniques. Fringe patterns are usually generated by a well-known phenomenon of optical interference. The surface of an object is then, reconstructed by analyzing the phase distribution of these fringe patterns- a process called phase extraction. To analyze the phase distributions in both spatial and spectral domains, pixel-wise phase shifting and global Fourier transform have been established as the two pillar techniques for fringe analysis. To use both the properties simultaneously, Windowed Fourier Transform (WFT) has emerged as an in-between technique to analyze the fringe patterns block by block. In the past decade, FPA has made great progress for 3D measurements. Several methods have been developed for 3D surface measurement based on varied principles. These include time of flight, laser triangulation, stereo vision, shape from focus and defocus, structured light projections and digital fringe projection (DFP). Among these, structured light fringe projections and digital fringe projections (DFP) are commonly used in fringe projection profi lometry (FPP) systems due to their simple setup and the ability to achieve high-speed and high-accuracy. However, two key issues still prevail which need further improvement. First, with the rapid demand for 3D reconstruction of object surfaces which can be readily applied and used in various applications such as virtual reality, animations, a precision inspection of optical components and many more, obtaining a high-speed and highly accurate surface measurement has become a necessity. Second, with several fringe analysis methods being developed over the past decades, it has become increasingly difficult to understand, analyze and introspect some of the best-suited applications and conditions where different fringe analysis methods can prove useful and thus, requires a link to be set up between different algorithms for further investigation. Both these issues revolve around a central idea: robustness and high-accuracy 3D measurement. Since the spectral information of a patch of fringe pattern is much simpler to analyze and thus, more effective, instead of resolving some of the major error sources in existing FPP systems in spatial and spectral domain separately, in this thesis, author proposes to use the local in-between Windowed Fourier Transform (WFT) technique for the same with an agenda to be able to investigate the link between some of the best suited techniques for various applications under certain measurement conditions. First, some state-of-the-art fringe analysis techniques are reviewed. Also, some major issues in fringe analysis for FPP systems are inspected such as nonlinear gamma, uneven background, edge discontinuity, and high dynamic range, and the existing state-of-the-art techniques for resolving these issues including both the phase-shifting and transform-based methods in the past decades are reviewed. It is found that the accuracy of measurement can be improved by either using a large number of fringe patterns or by iterating the algorithm many times thus, leaving scope for further improvement. Second, to resolve these error issues in fringe analysis one by one, we fi rst try to tackle nonlinear gamma errors caused by the nonlinear nature of the devices projector and camera. A theoretical analysis for resolving the nonlinear gamma errors using Windowed Fourier Ridges (WFR) for carrier phase demodulation is then proposed. It fi rst, analyzes the local frequency error and phase extraction error for the carrier fringe pattern in order to depict the amount of gamma nonlinearity and then, resolves the error with the help of a performance prediction and error control using WFR. It was observed that despite being challenging it is possible to reduce the peak phase error to be as low as 0.05 rad in the presence of the error source. Third, after tackling the issue of nonlinear gamma in single carrier fringe pattern, we then fi rst try to analyze nonlinear gamma in phase-shifting technique and thus, resolve the error by using WFR for phase-shifted fringe patterns which are squeezed to a single carrier fringe pattern. After that, uneven and discontinuous background is chosen as the second error source which needs to be resolved. To tackle this issue in a single carrier fringe pattern, a Windowed Fourier fi ltering (WFF) based background removal technique is proposed. It uses a mirroring approach to tackle the error around the corner pixels. An ideal window of (50, 50) is used for both the algorithms for effectively resolving the error sources. Fourth, after discussing the two major issues in fringe analysis, a comparative study is then performed between two state-of-the-art fringe analysis techniques - WFR and Sampling Moire (SM), to analyze the effectiveness of the two algorithms for a single carrier fringe pattern for the very first time. While SM converts a single carrier fringe pattern into multiple phase-shifted Moire patterns to demodulate phase, WFR obtains the phase information in the window-based Fourier domain. Despite appearing two completely different approaches for fringe analysis and despite having separate applications, both simulations and experimental results con rm that both the algorithms appear as two sides of the same coin and thus, can be used interchangeably in various applications. In the presence of noise, both algorithms give outstanding performance. Finally, a link between WFR and spatial carrier phase-shifting (SCPS) algorithm is proposed for the very first time. Since phase-shifting and Fourier transform are the two pillar techniques for fringe analysis, and as Windowed Fourier transform has already been established as the extension of the Fourier transform, it is crucial to understand the link between the two, in order to select a proper technique for effective fringe analysis. It is observed that whenever SCPS is used to analyze a fringe pattern, WFR can always be attempted for better results.Doctor of Philosoph


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    Windowed Fourier ridges as a spatial carrier phase-shifting algorithm

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    The windowed Fourier ridges (WFR) algorithm is shown to be a phase-shifting algorithm for phase extraction from a carrier fringe pattern. However, the former only provides a phase estimation with a controllable phase error, whereas the latter pursues exact phase extraction. This link not only is interesting but also enhances the understanding of different phase extraction techniques. Advantages and disadvantages of the WFRs algorithm are discussed.NRF (Natl Research Foundation, S’pore)Published versio

    Windowed Fourier ridges for demodulation of carrier fringe patterns with nonlinearity : a theoretical analysis

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    Accurately extracting phase or phase derivative is the most important requirement in optical metrology. However, in practice, there are many error sources, among which nonlinear distortion in fringe patterns is often encountered. Several techniques have been proposed over time to remove the nonlinearity error. Among these techniques, the windowed Fourier ridges (WFR) algorithm has been shown to be an effective solution insensitive to nonlinearity, but it lacks a theoretical justification. In this paper, we theoretically analyze the local frequency estimation error and phase extraction error, which not only proves the mentioned insensitivity, but also supports the performance prediction and error control, and thus is very important and useful in optical measurement. The theoretical results have been verified by computer simulations. Other error sources such as model error and noise are also compared and discussed

    Sampling moiré as a special windowed Fourier ridges algorithm in demodulation of carrier fringe patterns

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    In recent times, both the windowed Fourier ridges (WFR) and sampling moiré (SM) algorithms have been extensively used due to their high effectiveness in the demodulation of carrier fringe patterns. As they are developed independently, they are mostly recognized as completely different techniques, but we theoretically prove that SM is a special WFR with a specific window shape and a preset local frequency. This unifies the two different algorithms and enhances the understanding of their theoretical aspects, which helps to simplify the selection of these algorithms in real applications.Published versio

    OHVIRA syndrome with Orofacial clefts: a rare association

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    Obstucted hemivagina with ipsilateral renal anomaly (OHVIRA) syndrome or Herlyn-Werner-Wunderlich syndrome (HWW) is a rare congenital anomaly consist of uterus didelphys, obstructed hemivagina, and ipsilateral renal agenesis. We are reporting an adolescent girl with orofacial defect who presented with lower abdominal pain. She attained menarche 3 months earlier and had a regular menstrual cycle with cyclical abdominal pain. On abdominal examination a firm, mobile tender mass extending from left iliac fossa up to umbilicus (24 weeks size) was found.  Lower border of mass could not be approached. Further evaluation with ultrasound showed enlarged uterus with collection with internal echoes and non-visualization of the left kidney. CECT showed absent left kidney and didelphys uterus with large left hematocolpometra with left complex adenexal cyst. Patient was posted for hematocolpos drainage and vaginoplasty. An unusual presentation of regular menstruation and nonspecific abdominal pain delays the diagnosis, which can lead to severe complications such as endometriosis and infertility