Dar A. Roberts

Bio: Dar A. Roberts is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Vegetation & Hyperspectral imaging. The author has an hindex of 75, co-authored 329 publications receiving 22012 citations. Previous affiliations of Dar A. Roberts include University of Washington & University of California.

Edge Influence on Forest Structure and Composition in Fragmented Landscapes

Abstract: Although forest edges have been studied extensively as an important consequence of fragmenta- tion, a unifying theory of edge influence has yet to be developed. Our objective was to take steps toward the development of such a theory by (1) synthesizing the current knowledge of patterns of forest structure and composition at anthropogenically created forest edges, (2) developing hypotheses about the magnitude and distance of edge influence that consider the ecological processes influencing these patterns, and (3) identifying needs for future research. We compiled data from 44 published studies on edge influence on forest structure and composition in boreal, temperate, and tropical forests. Abiotic and biotic gradients near created forest edges generate a set of primary responses to edge creation. Indirect effects from these primary responses and the original edge gradient perpetuate edge influence, leading to secondary responses. Further changes in veg- etation affect the edge environment, resulting in ongoing edge dynamics. We suggest that the magnitude and distance of edge influence are a direct function of the contrast in structure and composition between adjacent communities on either side of the edge. Local factors such as climate, edge characteristics, stand attributes, and biotic factors affect patch contrast. Regional factors define the context within which to assess the ecological significance of edge influence (the degree to which the edge habitat differs from interior forest habitat). Our hypotheses will help predict edge influence on structure and composition in forested ecosystems, an important consideration for conservation. For future research on forest edges in fragmented landscapes, we encourage the testing of our hypotheses, the use of standardized methodology, complete descriptions of study sites, studies on other types of edges, synthesis of edge influence on different components of the ecosystem, and investigations of edges in a landscape context.

Using Imaging Spectroscopy to Study Ecosystem Processes and Properties

Abstract: Remote sensing data provide essential input for today's climate and ecosystem models. It is generally agreed that many model processes are not accurately depicted by current remotely sensed indices of vegetation and that new observational capabilities are needed at different spatial and spectral scales to reduce uncertainty. Recent advances in materials and optics have allowed the development of smaller, more stable, accurately calibrated imaging spectrometers that can quantify biophysical properties on the basis of the spectral absorbing and scattering characteristics of the land surface. Airborne and spaceborne imaging spectrometers, which measure large numbers (hundreds) of narrow spectral bands, are becoming more widely available from government and commercial sources; thus, it is increasingly feasible to use data from imaging spectroscopy for environmental research. In contrast to multispectral sensors, imaging spectroscopy produces quantitative estimates of biophysical absorptions, which ca...

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Image retrieval: Ideas, influences, and trends of the new age

Abstract: We have witnessed great interest and a wealth of promise in content-based image retrieval as an emerging technology. While the last decade laid foundation to such promise, it also paved the way for a large number of new techniques and systems, got many new people involved, and triggered stronger association of weakly related fields. In this article, we survey almost 300 key theoretical and empirical contributions in the current decade related to image retrieval and automatic image annotation, and in the process discuss the spawning of related subfields. We also discuss significant challenges involved in the adaptation of existing image retrieval techniques to build systems that can be useful in the real world. In retrospect of what has been achieved so far, we also conjecture what the future may hold for image retrieval research.

The Self-Organizing Map

Abstract: An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article.