Impacts of Positional Error on Spatial Regression Analysis: A Case Study of Address Locations in Syracuse, New York

Positional error is the error produced by the discrepancy between reference and recorded locations. In urban landscapes, locations typically are obtained from global positioning systems or geocoding software. Although these technologies have improved the locational accuracy of georeferenced data, they are not error free. This error affects results of any spatial statistical analysis performed with a georeferenced dataset. In this paper we discuss the properties of positional error in an address matching exercise and the allocation of point locations to census geography units. We focus on the error's spatial structure, and more particularly on impacts of error propagation in spatial regression analysis. For this purpose we use two geocoding sources, we briefly describe the magnitude and the nature of their discrepancies, and we evaluate the consequences that this type of locational error has on a spatial regression analysis of pediatric blood lead data for Syracuse, NY. Our findings include: (1) the confirmation of the recurrence of spatial clustering in positional error at various geographic resolutions; and, (2) the identification of a noticeable but not shockingly large impact from positional error propagation in spatial auto‐binomial regression analysis results for the dataset analyzed.     

Tidal waves in a canal of non-uniform depth

Summary This paper considers the propagation of a progressive tidal wave along a canal of uniform width, in which the depth increases linearly from one side to the other. The linearised tidal equations are solved firstly by a perturbation procedure for small inclinations of the bed to the horizontal, and secondly by a numerical method from the exact solution, for some particular values of the parameters.     

Tephrological implications of beam size—sample‐size effects in electron microprobe analysis of glass shards

This paper concerns the potential consequences of varying procedures for the determination of tephra geochemistry by electron microprobe. Application of electron probe microanalysis to tephrostratigraphical methods has increasingly facilitated the resolution and refinement of Quaternary chronology associated with records of proxy‐environmental or proxy‐climatic change. The geographical range over which tephras are recovered has expanded significantly with the identification and analysis of crypto (or hidden) tephras in areas far removed from tephra sources. These tephras are dominated by glass shards, which, in many distal environments, may be either small in size (μm) or may be highly pumiceous with low glass:void ratios and thin (<10 μm) shard walls. We demonstrate that reducing the size of the electron beam used to analyse shard geochemistry cannot be used reliably to permit analysis of thin glass walls. This approach distorts the geochemical data, creating analytical differences that may generate inappropriate tephrogeochemical fingerprints. Additional distortion of the geochemical fingerprint in the form of hybrid analyses may be encountered in glass fragments containing micron‐sized crystalline phases such as feldspar. Copyright © 2001 John Wiley & Sons, Ltd.     

Collision-induced absorption in the far infrared spectrum of Titan

The effects of collision-induced absorption on the far infrared spectrum of Titan have been investigated. After a review of the procedure for the theoretical calculation of the N₂ translation-rotational spectrum, new results for the temperature range of 70 to 120°K are reported. These are used as input data for a simple atmospheric model in order to compute the far infrared radiance, brightness temperature, and spectral limb function. This source of opacity alone is not capable of explaining the Voyager results. When the collision-induced methane is included, the results are in closer agreement in the range between 200 and 300 cm^?1, suggesting that a more complete treatment of collision-induced absorption including particularly CH₄N₂, N₂H₂, and H₂H₂ results, may provide sufficient opacity to reduce or obviate the need for opacities due to clouds or aerosols in order to explain the observed spectra.     

A description of persistent climatic anomalies in a 1000-year climatic model simulation

 The Mark 2 version of the CSIRO coupled global climatic model has been used to generate a 1000-year simulation of natural (i.e. unforced) climatic variability representative of “present conditions”. The annual mean output from the simulation has been used to investigate the occurrence of decadal and longer trends over the globe for a number of climatic variables. Here trends are defined to be periods of years with a climatic anomaly of a given sign. The analysis reveals substantial differences between the trend characteristics of the various climatic variables. Trends longer than 12 years duration were unusual for rainfall. Such trends were fairly uniformly distributed over the globe and had an asymmetry in the rate of occurrence for wet or dry conditions. On the other hand, trends in surface wind stress, and especially the atmospheric screen temperature, were of longer duration but primarily confined to oceanic regions. The trends in the atmospheric screen temperature could be traced deep into the oceanic mixed layer, implying large changes in oceanic thermal inertia. This thermal inertia then constituted an important component of the `memory' of the climatic system. While the geographic region associated with a given trend could be identified over several adjacent grid boxes of the model, regional plots for individual years of the trend revealed a range of variations, suggesting that a consistent forcing mechanism may not be responsible for a trend at a given location. Typical return periods for 12-year rainfall trends were once in 1000 years, highlighting the rarity of such events. Using a looser definition of a trend revealed that drying trends up to 50 years duration were also possible, attributable solely to natural climatic variability. Significant (∼20% to 40%) rainfall reductions per year can be associated with a long-term drying trend, hence such events are of considerable climatic significance. It can take more than 100 years for the hydrologic losses associated with such a trend to be overcome. Overall, the simulation provides new and useful insights into climatic trends, and quantifies a number of poorly observed characteristics. The results highlight the extensive and pervasive influence of unforced natural climatic variability as an omnipresent generator of climatic trends. Received: 20 January 2000 / Accepted: 21 September 2000     

Volatile organic compounds in Quaternary sediments

The distribution of volatile organic compounds in surface sediments varies widely with the depositional environment. Oxygen and sulfur compounds, alkenes and arenes, are more abundant than alkanes in strongly reducing sediments such as those from around Walvis Bay, West Africa. Among the compounds identified by GC-MS were toluene, benzene, 2-methyl-2-butene, 3,5-dimethylcyclopentene, 3-menthylfuran, 3-methylfuran, 2-methylbutanol, 3-methylbutanol, 3-pentanone, 2-methylthiophene, 3-methylthiophene and dimethylsulfide. Some of these compounds have the isoprene carbon skeleton.In a less reducing environment such as the Arabian Sea-Persian Gulf area, a more diverse alkene assemblage was observed including ethylene, propylene, pentenes, hexenes, cyclohexene, methylpentenes and dimethylcyclopentenes. Also, the sediments contained a few very specific alkane structures. The gem-dimethyl hydrocarbons (neopentane, neohexane, and neoheptane) were dominant among the branched hydrocarbons. The high concentration of volatile alkenes and oxygen and sulfur compounds is not observed in deep sea drilling samples at depths greater than about 100 m.     

The organic matter of a gulf coast well studied by a thermal analysis-gas chromatography technique

A thermal analysis-gas chromatography technique, previously described by Whelan et al. has been used to analyze cuttings from a Continental Offshore Stratigraphic Test (COST No. 1) drilled in the Gulf Coast of the U.S.A. The data allowed an evaluation of the degree of maturation of the organic matter and provided an accurate determination of the depth of the threshold of intense oil generation at 3048 m (10,000 ft.). Qualitative changes of hydrocarbons in the C₇–C₁₄ range were determined by gas chromatography and confirmed by gas chromatography-mass spectroscopy. These data are discussed in terms of generation and migration processes. The catagenetic evolution results in a strong tendency for a proportional increase in n-alkanes. Mass transfer phenomena may be responsible for updip movement of the lighter hydrocarbons.     

Generation and migration of hydrocarbons in offshore South Texas Gulf Coast sediments

The hydrocarbon content of two thick Tertiary sequences from the offshore Gulf Coast (South Padre Island and Mustang Island) was studied using a headspace technique, thermal distillation, pyrolysis and solvent extraction. The threshold of oil generation was determined to occur in the range of 3050 m (10,000 ft; 120°C) in Miocene sediments.In the South Padre Island well, the distribution of the different classes of hydrocarbons along the sedimentary column suggests some updip migration processes are occurring.