Analysis Of Topographic Features Research Articles

Grey seal (Halichoerus grypus) pup mortality not explained by local breeding density on North Rona, Scotland

AbstractPre‐weaning pup mortality of grey seals Halichoerus grypus in a breeding colony (North Rona, Scotland, U.K.) was examined in relation to the density of local adult females over two breeding seasons. Accurate, fine‐scale maps of daily seal locations within a GIS database permitted the extraction of measures of female density determined at a range of spatial scales from 5 to 50 m around each pup on the date of death. Adult densities around live pups provided the null distribution of adult densities, which were tested against the distribution of densities where deaths occurred. Pre‐weaning pup mortality at this colony was not related to any of our density measures. The proportion of pups dying each day showed no seasonal trends. Analysis of topographic features from a sub‐meter digital terrain model for locations where deaths occurred suggested that there were fewer mortalities in prime pupping habitats. This could have been a direct effect of habitat or the relative quality of mothers in these habitats. The distance separating mothers and pups tended to be greater on the periphery of the colony compared to more central areas. Pups in the peripheral areas may be more exposed to predation by gulls.

Mass detection in digitized mammograms using two independent computer-assisted diagnosis schemes.

Using two independent computer-assisted diagnosis (CAD) schemes, we investigated the potential to improve the sensitivity of mass detection by applying a logical "or" operation and to improve the specificity using a logical "and" operation. Two independent mass detectors, one with Gaussian bandpass filtering and multilayer topographic feature analysis and the other with a five-stage search for a single suspicious region, were applied to a large image database that included 428 digitized mammograms with 220 verified masses. The performance of the two schemes and a combination of them in the form of either logical "or" or logical "and" operations were compared. In this preliminary study, a multilayer topographic feature analysis CAD scheme (CAD-1) achieved a sensitivity of 96% and had a false-positive detection rate of 0.79 per image. A five-stage search method scheme (CAD-2) achieved a sensitivity of 94% and had a false-positive detection rate of 1.69 per image. With an "or" operation, the combined results yielded 100% sensitivity with a false-positive detection rate of 2.07 per image. A logical "and" operation produced a reduction of the false-positive detection rate to 0.4 per image, but sensitivity also decreased to 90%. Similar to an independent double-reading approach and depending upon the relevant clinical question, sensitivity or specificity can be improved by combining the results of several independent CAD schemes.

Computerized detection of masses in digitized mammograms using single-image segmentation and a multilayer topographic feature analysis

We developed and evaluated a computer-aided detection (CAD) scheme for masses in digitized mammograms. A multistep CAD scheme was developed and tested. The method uses a technique of single-image segmentation with Gaussian bandpass filtering to yield a high sensitivity for mass detection. A rule-based multilayer topographic feature analysis method is then used to classify suspected regions. A set of 260 cases, including 162 verified masses, was divided into two subsets; one set was used to set the rule-based classification and one was used to test the performance of the scheme. In a preliminary clinical study, the implemented detection scheme yielded 98% sensitivity with a false-positive detection rate of less than one false-positive region per image. Single-image segmentation methods seem to have high sensitivity in selecting true-positive mass regions in the first stage of a CAD scheme. A multilayer topographic image feature analysis method in the second stage of a CAD scheme has the potential to significantly reduce the false-positive detection rate.

Computer-aided detection of clustered microcalcifications in digitized mammograms

We investigated a computer-aided detection (CAD) scheme for clustered microcalcifications in digitized mammograms. A multistage CAD scheme was developed and tested. To increase sensitivity, the scheme uses a Gaussian band-pass filter and nonlinear threshold. A multistage local minimum searching routine and a multilayer topographic feature analysis are used to reduce the false-positive detection rate. One hundred ten digitized mammograms were used in this preliminary test, with 55 images containing one or two verified microcalcification clusters. The CAD scheme achieved 100% sensitivity and had an average false-positive detection rate of 0.18 per image. The CAD scheme performs as well as many published schemes and has some unique advantages to further improve detection sensitivity and specificity of future CAD schemes.

Object detection by step-wise analysis of spectral, spatial, and topographic features

In many computer vision systems accurate identification of various objects appearing in a scene is required. In this paper we address the problem of object detection in analyzing high resolution multispectral aerial images. Development of a practical object detection approach should consider issues of speed, accuracy, robustness, and amount of supervision allowed. The approach is based upon extraction of information from images and their systematic analysis utilizing available prior knowledge of various physical attributes of the objects. The step-wise approach examines spectral, spatial, and topographic features in making the object vs background decision. Techniques for the analysis of the spectral, spatial, and topographic features tend to be of increasing levels of computational complexity. The computationally simpler spectral feature analysis is performed for the entire image to detect candidate object regions. Only these regions are considered in the spatial feature analysis step to further reduce the number of candidate regions which need to be analyzed in the topographic feature analysis step. Such step-wise analysis makes the entire object detection process efficient by incorporating the process of “focus of attention” to identify regions of interest thus eliminating a relatively large portion of image from further detailed examination at every stage. Results of the experiments performed using several high resolution multispectral images have demonstrated the basic feasibility of the approach. The images utilized in the experiments are acquired from geographically different locations, at different times, with different types of background, and are of different resolution. Successful object detection with high accuracy and low false alarm rates indicate the robustness of this approach.

SEDIMENT MOVEMENT ON THE KUROBE ALLUVIAL FAN

Sediment movement on the KUROBE alluvial fan is estimated. The results lead to the broad understanding of the relation between the transition of topography in a long term and the river characteristics at the present time. The analysis of topographic features is shown to be usefull for the long term river planning.

TOPOGRAPHY OF THE FOOD‐REINFORCED KEY PECK AND THE SOURCE OF 30‐MILLISECOND INTERRESPONSE TIMES1

High-speed photography of key pecking revealed that the arc described by the upper bill as a pigeon closes its beak is capable of operating a Lehigh Valley pigeon key set at 8 to 14 g. Arc-produced switch closure follows initial switch closure in less than 50 msec. When birds were trained on ratio schedules, the probability of interresponse times (IRTs) shorter than 50 msec exceeded 0.30. Interval-trained birds produced a much lower probability of short-IRTs. When the schedules were reversed, there was only weak evidence of a reversal in the probability of short IRTs. A temporal analysis of topographic features observed in the original photographs failed to reveal differences between ratio and interval pecking topography. It appeared that only the point of contact with the key differed between subjects trained on the two schedules. It was concluded that only the locus, but not the topography, of the food-reinforced key peck was modified by the schedule of reinforcement.