Investigating DEM Error Patterns by Directional Variograms and Fourier Analysis

In many spatial analyses and GIS applications, a Digital Elevation Model (DEM) is often used to derive a variety of new variables and parameters. Previous research shows that the accuracy of derived variables is affected, not merely by the magnitude of DEM errors and the algorithms applied to derive these variables, but also by the spatial structure of DEM errors. However, the lack of knowledge and understanding of the spatial structure of DEM errors often handicaps the analysis of error propagation. This paper investigates the spatial autocorrelation and anisotropic pattern of DEM error by using directional variograms in the spatial domain and Fourier analysis in the frequency domain. Based on an empirical study, it is concluded that the spatial autocorrelation pattern of DEM errors is anisotropic and scale-dependent, and that the maximum direction and range of the autocorrelation depends upon the orientation and wavelength of the terrain features. For a smooth terrain, the magnitude of DEM errors is correlated to surface slope. For a rugged terrain, the elevation values in DEMs tend to be underestimated in ridges, and overestimated in valleys, but the correlation between the DEM error and surface slope is quite low.     

Strontium isotopic reconstruction of the composition of an urban free black population from the 19th century United States

The Industrial Revolution in the United States had a tremendous impact on society, altering not only economics but also the distribution of it population. It was also during this period that increasing numbers of African Americans gained their freedom from slavery. Released from overt bondage, free African Americans sought the opportunities denied to them for over two centuries, initiating a large scale movement of people to the burgeoning urban centers of industry. The individuals interred in the Newburgh Colored Burial Ground (1830–1870) represent one small segment of this process. Strontium isotopic analyses are utilized in order to discuss the demographic composition of Newburgh’s free black population during this time period. In particular, we examine the relative contribution of migration and natural increase, and whether there are significant sex-specific differences in the formation of the population. The results suggest that Newburgh’s free black population was composed predominantly of individuals born in the immediate region. Additionally, there were a greater percentage of non-local males than females. While historical data suggests that females had greater job opportunities in the north relative to males, the growing industrial economy Newburgh may very well have fostered greater male mobility.     

Relative and absolute dating of the human skull and skeleton from Galley Hill,Kent

Over a period of some 100 years it has gradually been accepted that the human skeletal remains found in the late nineteenth century in ancient gravels at Galley Hill, Kent are not those of early man, but are of much more recent date. This conclusion was finally verified by means of relative (N, F) and absolute (¹⁴C) dating. Here we present the results of further analysis of the remains from Galley Hill for their uranium content by a method having general application to the relative dating of fossil human and other mammalian bone.