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Trends and Interannual Variability of Winds and Turbulent Heat Flux in the Indian Ocean Sector of Southern Ocean during 2000-2009

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Atmospheric and Climate Sciences 2014年第2期4卷 290-304页

作者： alvarinho j. luis Earth System Science Organization-National Centre for Antarctic and Ocean Research Ministry of Earth Sciences Government of India Headland Sada India

Using satellite-based wind and sea surface temperature (SST) observations, linear trend and inter-annual variability of wind stress, turbulent heat flux (Q) and wind stress curl are addressed for the Indian Ocean sector of the Southern Ocean (ISO, 0°E - 155°E) for the period 2000-2009. The analysis reveals that spatial mean of Q varies between 70 and 73 Wm-2 in the austral summer and winter, respectively, while the mean wind stress is nearly same at 0.22 Nm-2 for both seasons. The anticyclonic curl dominates the ISO, which increases from 0.15 × 10-7 to 0.35 × 10-7 Nm-3 during the austral summer. The detrended box-mean time series of Q, wind stress, and wind stress curl exhibits a decreasing trend of –6.3 ± 1.6 Wm-2·decade-1, -0.012 ± 0.004 Nm-2·decade-1 and -0.48 ± 0.6 × 10-8 Nm-3·decade-1, respectively. The Empirical Orthogonal Function (EOF) analysis was carried out to study inter-annual variability. EOF-1 of Q captures 25% of the total variance, which mimics the austral summer pattern;its time coefficient is highly and negatively correlated with a 2-month lagged Nino3.4 SST index (r =-0.8 at 95% confidence). EOF-1 of wind stress accounts for 35% of the total variance and its time coefficient is strongly correlated with the Antarctic Oscillation (r= 0.86 at 95% confidence). EOF-1 of wind stress curl captures 15% of the total variance;its time coefficient is correlated to the Nino3.4 SST index (r= 0.65 at 95% confidence) with the former lagging the latter by two years. The repercussions of the weakening trends of the climatic parameters on the air-sea interaction and ocean circulation are highlighted.

关键词： Southern Ocean Interannual Variability Meteorology Empirical Orthogonal Function Analysis

The Role of the Southern Hemisphere Polar Cell on Antarctic Sea Ice Variability

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International j.urnal of Geosciences 2016年第2期7卷 120-134页

作者： Praveen Rao Teleti alvarinho j. luis Earth System Science Organization National Centre for Antarctic and Ocean Research Ministry of EarthSciences Govt. of India Headland Sada Goa India

The study explores modes of variability in the Southern Polar Cell and their relationship with known global climate modes and Antarctic sea ice. It is found that Polar Cell is barotropic in nature and 500 hPa geo-potential height (Z500) field can satisfactorily represent variability in the Polar Cell. First, three leading Empirical Orthogonal Function (EOF) modes of Z500 account for nearly 80% of observed variability in the Polar Cell. Dominant mode (PC1500) comprises of high pressure divergence zone over Antarctica. Second leading mode (PC2500) is low pressure zone covering Amundsen-Bellingshausen Sea (ABS) similar to ABS low feature. A new climate mode called Polar Coastal Index (PCI) is defined, which describes more than 15% and close to 30% variability of circumpolar trough and ABS low, respectively. Out of four modes defined in this study, only PCI and PC2500 show linear trends and clear seasonality. Interestingly, both modes are affected by modulation of ABS low due to tropical ENSO forcing. SAM signature is present in Polar Cell as PC1500 shares large variance with it. The largest impact on sea ice comes from PC2500 followed by PC1500 in the Antarctic Dipole regions. However, this study suggests contemporary sea ice trends cannot be sustained, and can reverse given that trends in PCI and PC2500 favour a reversal. These results indicate that ENSO-driven Polar Cell variability plays a crucial role influencing Antarctic sea ice as it interacts with other climate modes and leads the combined impact at the interannual time scale.

关键词： Antarctica Sea Ice Polar Cell PCI ENSO Teleconnection

Sea Ice Observations in Polar Regions: Evolution of Technologies in Remote Sensing

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International j.urnal of Geosciences 2013年第7期4卷 1031-1050页

作者： Praveen Rao Teleti alvarinho j. luis Earth System Sciences Organization National Centre for Antarctic and Ocean Research Ministry of Earth Sciences Goa India

Evolution of remote sensing sensors technologies is presented, with emphasis on its suitability in observing the polar regions. The extent of influence of polar regions on the global climate and vice versa is the spearhead of climate change research. The extensive cover of sea ice has maj.r impacts on the atmosphere, oceans, and terrestrial and marine ecosystems of the polar regions in particular and teleconnection on other processes elsewhere. Sea ice covers vast areas of the polar oceans, ranging from ~18 × 106 km2 to ~23 × 106 km2, combined for the Northern and Southern Hemispheres. However, both polar regions are witnessing contrasting rather contradicting effects of climate change. The Arctic sea ice extent is declining at a rate of 0.53 × 106 km2·decade–1, whereasAntarcticaexhibits a positive trend at the rate of 0.167 × 106 km2·decade–1. This work reviews literature published in the field of sea ice remote sensing, to evaluate and access success and failures of different sensors to observe physical features of sea ice. The chronological development series of different sensors on different satellite systems, sensor specifications and datasets are examined and how they have evolved to meet the growing needs of users is outlined. Different remote sensing technology and observational methods and their suitability to observe specific sea ice property are also discussed. A pattern has emerged, which shows that microwave sensors are inherently superior to visible and infrared in monitoring seasonal and annual changes in sea ice. Degree of successes achieved through remote sensing techniques by various investigators has been compared. Some technologies appear to work better under certain conditions than others, and it is now well accepted that there is no algorithm that is ideal globally. Contribution of Indian remote sensing satellites is also reviewed in the context of polar research. This review suggests different primary datasets for further research on sea ice f

关键词： Sea Ice Satellite Remote Sensing Polar Regions Albedo

A Comprehensive Evaluation of PAN-Sharpening Algorithms Coupled with Resampling Methods for Image Synthesis of Very High Resolution Remotely Sensed Satellite Data

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Advances in Remote Sensing 2013年第4期2卷 332-344页

作者： Shridhar D. j.wak alvarinho j. luis Polar Remote Sensing Department Earth System Sciences Organization (ESSO) National Centre for Antarctic and Ocean Research (NCAOR) Ministry of Earth Sciences Government of India Headland Sada Gao India

The merging of a panchromatic (PAN) image with a multispectral satellite image (MSI) to increase the spatial resolution of the MSI, while simultaneously preserving its spectral information is classically referred as PAN-sharpening. We employed a recent dataset derived from very high resolution of WorldView-2 satellite (PAN and MSI) for two test sites (one over an urban area and the other over Antarctica), to comprehensively evaluate the performance of six existing PAN-sharpening algorithms. The algorithms under consideration were the Gram-Schmidt (GS), Ehlers fusion (EF), modified hue-intensity-saturation (Mod-HIS), high pass filtering (HPF), the Brovey transform (BT), and wavelet-based principal component analysis (W-PC). Quality assessment of the sharpened images was carried out by using 20 quality indices. We also analyzed the performance of nearest neighbour (NN), bilinear interpolation (BI), and cubic convolution (CC) resampling methods to test their practicability in the PAN-sharpening process. Our results indicate that the comprehensive performance of PAN-sharpening methods decreased in the following order: GS > W-PC > EF > HPF > Mod-HIS > BT, while resampling methods followed the order: NN > BI > CC.

关键词： PAN-Sharpening WorldView-2 Resampling Methods

Hydrodynamics between Africa and Antarctica during Austral Summer of 2008 and 2009: Results of the IPY Proj.ct

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International j.urnal of Geosciences 2013年第2期4卷 494-510页

作者： alvarinho j. luis S. M. Pednekar National Centre for Antarctic and Ocean Research (NCAOR) Earth System Science Organization Ministry of Earth Sciences Government of India New Delhi India

A hydrographic section between Cape Town,South AfricaandIndiaBay,Antarcticawas sampled by deploying expendable CTD probes during the austral summer of 2008 and 2009. In 2009, the Agulhas Retroflection (AR) Front was displaced southward by 1.5° latitude, while the northern and southern Polar Front meandered southward by 1° and 1.4° latitude, respectively, relative to their positions in 2008. Geostrophic transport, relative to1000 m, indicates that Antarctic Circumpolar Current (ACC) flow decreased by 2.5 Sv in 2009 compared to that in 2008. The anticyclones which are detached from the AR facilitates a transport to the southeast Atlantic Ocean ranging between 8 and 12 Sv. Nearly 50% of the ACC transport is confined to the 100 - 500 m layer. A comparison of water mass distribution for 2008 and 2009 suggests that Mode Water distribution was restricted to 42.5°S and 41.9°S, and the Antarctic Surface Water ex°tended to 57.6°S and 46.6°S, respectivel°. In 2009, the along track Heat Content (HC) and Salt Content (SC) for the upper750 mof the water column decreased each by 1% compared to those in 2008. In the ACC domain, the HC and SC dip by 36% and 40% in 2009, respectively. The HC and SC associated with Agulhas Retroflection Front increase in 2009 by 1% and 2%, respectively, due to an enhanced Agulhas transport of warm and saline water from the tropics by 2%.

关键词： Component Formatting Style Styling Insert

A Comprehensive Review on Pixel Oriented and Obj.ct Oriented Methods for Information Extraction from Remotely Sensed Satellite Images with a Special Emphasis on Cryospheric Applications

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Advances in Remote Sensing 2015年第3期4卷 177-195页

作者： Shridhar D. j.wak Prapti Devliyal alvarinho j. luis Earth System Science Organization (ESSO) National Centre for Antarctic & Ocean Research (NCAOR) Ministry of Earth Sciences Government of India Vasco da Gama India Department of Civil Engineering Symbiosis Institute of Technology Symbiosis International University Pune India

Image classification is one of the most basic operations of digital image processing. The present review focuses on the strengths and weaknesses of traditional pixel-based classification (PBC) and the advances of obj.ct-oriented classification (OOC) algorithms employed for the extraction of information from remotely sensed satellite imageries. The state-of-the-art classifiers are reviewed for their potential usage in urban remote sensing (RS), with a special focus on cryospheric applications. Generally, classifiers for information extraction can be divided into three catalogues: 1) based on the type of learning (supervised and unsupervised), 2) based on assumptions on data distribution (parametric and non-parametric) and, 3) based on the number of outputs for each spatial unit (hard and soft). The classification methods are broadly based on the PBC or the OOC approaches. Both methods have their own advantages and disadvantages depending upon their area of application and most importantly the RS datasets that are used for information extraction. Classification algorithms are variedly explored in the cryosphere for extracting geospatial information for various logistic and scientific applications, such as to understand temporal changes in geographical phenomena. Information extraction in cryospheric regions is challenging, accounting to the very similar and conflicting spectral responses of the features present in the region. The spectral responses of snow and ice, water, and blue ice, rock and shadow are a big challenge for the pixel-based classifiers. Thus, in such cases, OOC approach is superior for extracting information from the cryospheric regions. Also, ensemble classifiers and customized spectral index ratios (CSIR) proved extremely good approaches for information extraction from cryospheric regions. The present review would be beneficial for developing new classifiers in the cryospheric environment for better understanding of spatial-temporal changes over lon

关键词： Pixel Based Classification Obj.ct Oriented Classification Cryosphere Antarctica

A Review on Extraction of Lakes from Remotely Sensed Optical Satellite Data with a Special Focus on Cryospheric Lakes

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Advances in Remote Sensing 2015年第3期4卷 196-213页

作者： Shridhar D. j.wak Kamana Kulkarni alvarinho j. luis Polar Remote Sensing Division Earth System Science Organization (ESSO) National Centre for Antarctic & Ocean Research (NCAOR) Ministry of Earth Sciences Vasco da Gama India School of Electronics Devi Ahilya Vishwavidyalaya Indore India

Water on the Earth’s surface is an essential part of the hydrological cycle. Water resources include surface waters, groundwater, lakes, inland waters, rivers, coastal waters, and aquifers. Monitoring lake dynamics is critical to favor sustainable management of water resources on Earth. In cryosphere, lake ice cover is a robust indicator of local climate variability and change. Therefore, it is necessary to review recent methods, technologies, and satellite sensors employed for the extraction of lakes from satellite imagery. The present review focuses on the comprehensive evaluation of existing methods for extraction of lake or water body features from remotely sensed optical data. We summarize pixel-based, obj.ct-based, hybrid, spectral index based, target and spectral matching methods employed in extracting lake features in urban and cryospheric environments. To our knowledge, almost all of the published research studies on the extraction of surface lakes in cryospheric environments have essentially used satellite remote sensing data and geospatial methods. Satellite sensors of varying spatial, temporal and spectral resolutions have been used to extract and analyze the information regarding surface water. Multispectral remote sensing has been widely utilized in cryospheric studies and has employed a variety of electro-optical satellite sensor systems for characterization and extraction of various cryospheric features, such as glaciers, sea ice, lakes and rivers, the extent of snow and ice, and icebergs. It is apparent that the most common methods for extracting water bodies use single band-based threshold methods, spectral index ratio (SIR)-based multiband methods, image segmentation methods, spectral-matching methods, and target detection methods (unsupervised, supervised and hybrid). A Synergetic fusion of various remote sensing methods is also proposed to improve water information extraction accuracies. The methods developed so far are not generic rather they a

关键词： Cryospehere Remote Sensing Semi-Automatic Extraction Lakes Spectral Index Ratio

Validation of High-Density Airborne LiDAR-Based Feature Extraction Using Very High Resolution Optical Remote Sensing Data

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Advances in Remote Sensing 2013年第4期2卷 297-311页

作者： Shridhar D. j.wak Satej.N. Panditrao alvarinho j. luis Centre for Environmental Planning & Technology (CEPT) University Ahmedabad India Earth System Sciences Organization National Centre for Antarctic and Ocean Research (NCAOR) Ministry of Earth Sciences Government of India Headland Sada Goa India

This work uses the canopy height model (CHM) based workflow for individual tree crown delineation from LiDAR point cloud data in an urban environment and evaluates its accuracy by using very high-resolution PAN (spatial) and 8-band WorldView-2 imagery. LiDAR point cloud data were used to detect tree features by classifying point elevation values. The workflow includes resampling of LiDAR point cloud to generate a raster surface or digital terrain model, generation of hill-shade image and intensity image, extraction of digital surface model, generation of bare earth digital elevation model and extraction of tree features. Scene dependent extraction criteria were employed to improve the tree feature extraction. LiDAR-based refining/filtering techniques used for bare earth layer extraction were crucial for improving the subsequent tree feature extraction. The PAN-sharpened WV-2 image (with 0.5 m spatial resolution) used to assess the accuracy of LiDAR-based tree features provided an accuracy of 98%. Based on these inferences, we conclude that the LiDAR-based tree feature extraction is a potential application which can be used for understanding vegetation characterization in urban setup.

关键词： LiDAR WorldView-2 Feature Extraction

A Review on Applications of Imaging Synthetic Aperture Radar with a Special Focus on Cryospheric Studies

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Advances in Remote Sensing 2015年第2期4卷 163-175页

作者： Shridhar D. j.wak Tushar G. Bidawe alvarinho j. luis Polar Remote Sensing Division Earth System Science Organization (ESSO) National Centre for Antarctic & Ocean Research (NCAOR) Ministry of Earth Sciences Vasco-Da-Gama India Department of Civil Engineering Symbiosis Institute of Technology Symbiosis International University Pune India

The cryosphere is the frozen part of the Earth’s system. Snow and ice are the main constituents of the cryosphere and may be found in different states, such as snow, freshwater ice, sea ice, perma-frost, and continental ice masses in the form of glaciers and ice sheets. The present review mainly deals with state-of-the-art applications of synthetic aperture radar (SAR) with a special emphasize on cryospheric information extraction. SAR is the most important active microwave remote sensing (RS) instrument for ice monitoring, which provides high-resolution images of the Earth’s surface. SAR is an ideal sensor in RS technology, which works in all-weather and day and night conditions to provide useful unprecedented information, especially in the cryospheric regions which are almost inaccessible areas on Earth. This paper addresses the technological evolution of SAR and its applications in studying the various components of the cryosphere. The arrival of SAR radically changed the capabilities of information extraction related to ice type, new ice formation, and ice thickness. SAR applications can be divided into two broad classes-polarimetric applications and interferometric applications. Polarimetric SAR has been effectively used for mapping calving fronts, crevasses, surface structures, sea ice, detection of icebergs, etc. The paper also summarizes both the operational and climate change research by using SAR for sea ice parameter detection. Digital elevation model (DEM) generation and glacier velocity mapping are the two most important applications used in cryosphere using SAR interferometry or interferometric SAR (InSAR). Space-borne InSAR techniques for measuring ice flow velocity and topography have developed rapidly over the last decade. InSAR is capable of measuring ice motion that has radically changed the science of glaciers and ice sheets. Measurement of temperate glacier velocities and surface characteristics by using airborne and space-borne interferometric

关键词： Cryosphere Remote Sensing Synthetic Aperture Radar (SAR) Polarimetric SAR Interferometric SAR