Trajectory-based change detection for automated characterization of forest disturbance dynamics

Satellite sensors are well suited to monitoring changes on the Earth's surface through provision of consistent and repeatable measurements at a spatial scale appropriate for many processes causing change on the land surface. Here, we describe and test a new conceptual approach to change detection of forests using a dense temporal stack of Landsat Thematic Mapper (TM) imagery. The central premise of the method is the recognition that many phenomena associated with changes in land cover have distinctive temporal progressions both before and after the change event, and that these lead to characteristic temporal signatures in spectral space. Rather than search for single change events between two dates of imagery, we instead search for these idealized signatures in the entire temporal trajectory of spectral values. This trajectory-based change detection is automated, requires no screening of non-forest area, and requires no metric-specific threshold development. Moreover, the method simultaneously provides estimates of discontinuous phenomena (disturbance date and intensity) as well as continuous phenomena (post-disturbance regeneration). We applied the method to a stack of 18 Landsat TM images for the 20-year period from 1984 to 2004. When compared with direct interpreter delineation of disturbance events, the automated method accurately labeled year of disturbance with 90% overall accuracy in clear-cuts and with 77% accuracy in partial-cuts (thinnings). The primary source of error in the method was misregistration of images in the stack, suggesting that higher accuracies are possible with better registration.     

A clustering procedure for exploratory mining of vector time series

A two-step procedure is developed for the exploratory mining of real-valued vector (multivariate) time series using partition-based clustering methods. The proposed procedure was tested with model-generated data, multiple sensor-based process data, as well as simulation data. The test results indicate that the proposed procedure is quite effective in producing better clustering results than a hidden Markov model (HMM)-based clustering method if there is a priori knowledge about the number of clusters in the data. Two existing validity indices were tested and found ineffective in determining the actual number of clusters. Determining the appropriate number of clusters in the case that there is no a priori knowledge is a known unresolved research issue not only for our proposed procedure but also for the HMM-based clustering method and further development is necessary.     

Spatial, spectral and temporal patterns of tropical forest cover change as observed with multiple scales of optical satellite data

This article describes the development of a methodology for scaling observations of changes in tropical forest cover to large areas at high temporal frequency from coarse resolution satellite imagery. The approach for estimating proportional forest cover change as a continuous variable is based on a regression model that relates multispectral, multitemporal MODIS data, transformed to optimize the spectral detection of vegetation changes, to reference change data sets derived from a Landsat data record for a study site in Central America. A number of issues involved in model development are addressed here by exploring the spatial, spectral and temporal patterns of forest cover change as manifested in a time-series of multi-scale satellite imagery.The analyses highlighted the distinct spectral change patterns from year-to-year in response to the possible land cover trajectories of forest clearing, regeneration and changes in climatic and land cover conditions. Spectral response in the MODIS Calibrated Radiances Swath data set followed more closely with the expected patterns of forest cover change than did the spectral response in the Gridded Surface Reflectance product. With forest cover change patterns relatively invariant to the spatial grain size of the analysis, the model results indicate that the best spectral metrics for detecting tropical forest clearing and regeneration are those that incorporate shortwave infrared information from the MODIS calibrated radiances data set at 500-m resolution, with errors ranging from 7.4 to 10.9% across the time periods of analysis.     

Data fitting with geometric-programming-compatible softmax functions

Motivated by practical applications in engineering, this article considers the problem of approximating a set of data with a function that is compatible with geometric programming (GP). Starting with well-established methods for fitting max-affine functions, it is shown that improved fits can be obtained using an extended function class based on the softmax of a set of affine functions. The softmax is generalized in two steps, with the most expressive function class using an implicit representation that allows fitting algorithms to locally tune softness. Each of the proposed function classes is directly compatible with the posynomial constraint forms in GP. Max-monomial fitting and posynomial fitting are shown to correspond to fitting special cases of the proposed implicit softmax function class. The fitting problem is formulated as a nonlinear least squares regression, solved locally using a Levenberg–Marquardt algorithm. Practical implementation considerations are discussed. The article concludes with numerical examples from aerospace engineering and electrical engineering.     

Foreword: Hearsay testimony in trials involving child witnesses.

Allowing hearsay testimony in child abuse cases represents a dramatic and controversial change to the legal system, yet little scholarly and empirical work has been devoted to the topic. This special theme issue contains 12 articles written by psycholegal scholars from the United States, United Kingdom, and Canada. It is organized to address 3 basic issues that should be of interest to psycholegal. researchers, as well as police officers, judges, lawyers, and other members of the legal community. (a) How often is hearsay testimony used? How is it used in comparison to other innovations designed to protect the psychological welfare of the child witness? (b) How accurate is hearsay testimony? Is it as accurate as the child's own account? (c) Do jurors believe hearsay testimony? How much weight do or should jurors give to hearsay testimony? Two critical commentaries, one legal and one psychological, follow these articles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In This Issue

Software Quality Journal -     

Numerical simulations of laser wakefield accelerators in optimal Lorentz frames

The simulation of laser wakefield accelerators with particle-in-cell codes in relativistic reference frames is described, with emphasis on the computational speed-ups, which may potentially exceed three orders of magnitude in comparison with laboratory frame configurations. The initialization of laboratory quantities in a relativistically moving frame is depicted, and the method for result comparison with the plasma rest frame is described. Benchmarks with laboratory frame simulations and experimental data where gains of ∼20 times were obtained are discussed, and potential numerical issues are analyzed. This method enables numerical simulations with shorter turnaround times required for parameter scanning, and for one-to-one three-dimensional experimental modeling of current and next generation laser wakefield experiments.     

Innovative Data Acquisition for Heavily Instrumented Flexible Pavements

A data acquisition program was written to allow independent triggering of multiple test sections of a thin flexible pavement. A total of 129 electronic sensors were installed in 17 test sections and subjected to 2,100 truck passes over several months immediately after construction. The measured strains were highly variable in the thin flexible pavement, but the program was still able to successfully trigger each section independently. The majority of signal processing was also performed within the program, which was written in Lab VIEW 7 Express. This approach significantly reduced the amount of postprocessing effort that would have otherwise been required. The quality of the triggering approach was compared to independently collected weigh in motion data. The majority of the test sections recorded within 0.5% of the number of vehicles recorded by the weigh in motion system. Key components of all major facets of the data acquisition and programming performed are discussed in detail.     

Parental Mediation of Children's Television Viewing in Low-Income Families

Studies of parental mediation of children's television viewing have included samples of mostly middle- and upper-class Caucasian parents. These studies have only begun to examine mediation in the context of parent-child relationships. This study of 306 low-income, predominately African American mothers assesses macro- and microlevel influences on viewing mediation using Bronfenbrenner's ecological theory of child development. It was hypothesized that factors outside the home (e.g., work hours) influence parents' involvement with children, which, in turn, was predicted to influence viewing mediation. Results supported this model for coviewing and instructive mediation, but not for viewing restrictions.