Toward estimation of map accuracy without a probability test sample

The time and effort required of probability sampling for accuracy assessment of large-scale land cover maps often means that probability test samples are not collected. Yet, map usefulness is substantially reduced without reliable accuracy estimates. In this article, we introduce a method of estimating the accuracy of a classified map that does not utilize a test sample in the usual sense, but instead estimates the probability of correct classification for each map unit using only the classification rule and the map unit covariates. We argue that the method is an improvement over conventional estimators, though it does not eliminate the need for probability sampling. The method also provides a new and simple method of constructing accuracy maps. We illustrate some of problems associated with accuracy assessment of broad-scale land cover maps, and our method, with a set of nine Landsat Thematic Mapper satellite image-based land cover maps from Montana and Wyoming, USA.     

Air Particulates Associated with the Ash Whitefly

Unusual air particulates are linked to recent heavy infestations of the ash whitefly in California using high-performance liquid chromatography, scanning electron microscopy, optical and infrared microscopy, ion chromatography and X-ray fluorescence spectrometry. The unusual particles apparently are microdroplets of ash whitefly honeydew. Most of the suspended honeydew is in microdroplets with diameters between about two and twenty microns. The microdroplets were found to contain substantial amounts of sugars, primarily the oligosaccharides stachyose and raffinose. They also contain about 1 percent potassium, mainly as K⁺ The unusual microdroplets have been found in samples of air particulates taken in many areas of California after 1988.

Using a receptor model, the suspended honeydew was calculated to add as much as 40 microgm/M³ to PM₁₀ mass. The highest levels of suspended honeydew occurred between late August and early November.     

Predictive modelling of NAPL injection tests in variable aperture spatially correlated fractures.

In preparation for a field experiment where a NAPL will be injected into a fractured sandstone aquifer, a 2D invasion percolation model of DNAPL migration in a single horizontal fracture with varying aperture has been developed. This simulation investigated the effect of spatially correlated fracture aperture fields on pressure-saturation relationships as a function of variable aperture mean, standard deviation, and spatial correlation statistics under hydrostatic conditions. Results from spatially correlated variable aperture fields can be significantly different from random fields. Longer ranges decreased entry pressures and higher standard deviations decreased nonwetting phase saturations. Mean aperture is the major control on displacement pressure, entry pressure and the form of the pressure-saturation curve. Simulation results using statistical parameters for a variable aperture natural sandstone fracture as described by Yeo et al. [International Journal of Rock Mechanics and Mining Sciences 35 (1998) 1051] closely resemble a Brooks-Corey pressure-saturation function, and exhibit a distinct entry pressure followed by a rapid increase in nonwetting phase saturation. Graphical estimates of entry pressure provide a good approximation of the critical aperture controlling the formation of a continuous nonwetting phase pathway in a variable aperture fracture. Consequently, we show that multiphase flow concepts developed for porous media can successfully be applied to variable aperture fractures. Entry pressure correlates well to the mean aperture in these simulations when using a Gaussian distribution of fracture aperture. Interpreted aperture distributions from NAPL injection experiments do not fit the true distribution well at low nonwetting phase saturations, but do at higher saturations above the entry pressure. Consequently, true, mechanical aperture variation within a fracture plane cannot be determined from NAPL injection experiments either in the field or laboratory.     

Determinants of seed removal distance by scatter-hoarding rodents in deciduous forests

Scatter-hoarding rodents should space food caches to maximize cache recovery rate (to minimize loss to pilferers) relative to the energetic cost of carrying food items greater distances. Optimization models of cache spacing make two predictions. First, spacing of caches should be greater for food items with greater energy content. Second, the mean distance between caches should increase with food abundance. However, the latter prediction fails to account for the effect of food abundance on the behavior of potential pilferers or on the ability of caching individuals to acquire food by means other than recovering their own caches. When considering these factors, shorter cache distances may be predicted in conditions of higher food abundance. We predicted that seed caching distances would be greater for food items of higher energy content and during lower ambient food abundance and that the effect of seed type on cache distance variation would be lower during higher food abundance. We recorded distances moved for 8636 seeds of five seed types at 15 locations in three forested sites in Pennsylvania, USA, and 29 forest fragments in Indiana, U.S.A., across five different years. Seed production was poor in three years and high in two years. Consistent with previous studies, seeds with greater energy content were moved farther than less profitable food items. Seeds were dispersed less far in seed-rich years than in seed-poor years, contrary to predictions of conventional models. Interactions were important, with seed type effects more evident in seed-poor years. These results suggest that, when food is superabundant, optimal cache distances are more strongly determined by minimizing energy cost of caching than by minimizing pilfering rates and that cache loss rates may be more strongly density-dependent in times of low seed abundance.     

Exhaust temperature profiles for application of passive diesel particulate filters to solid waste collection vehicles in California

To reduce public exposure to diesel particulate matter (DPM), the California Air Resources Board has begun adoption of a series of rules to reduce these emissions from in-use heavy-duty vehicles. Passive diesel particulate filter (DPF) after-treatment technologies are a cost-effective method to reduce DPM emissions and have been used on a variety of vehicles worldwide. Two passive DPFs were interim-verified in California and approved federally for use in most 1994--2002 engine families for vehicles meeting min engine exhaust temperature requirements for successful filter regeneration. Some vehicles, however, may not be suited to passive DPFs because of lower engine exhaust temperatures. The purpose of this study was to determine the applicability of two types of passive DPFs to solid waste collection vehicles, the group of vehicles for which California recently mandated in-use DPM reductions. We selected 60 collection vehicles to represent the four main types of collection vehicle duty cycles--rolloffs, and front-end, rear, and side loaders--and collected second-by-second engine exhaust temperature readings for one week from each vehicle. As a group, the collection vehicles exhibited low engine exhaust temperatures, making the application of passive DPFs to these vehicles difficult. Only 35% of tested vehicles met the temperature requirements for one passive DPF, whereas 60% met the temperature requirements for the other. Engine exhaust temperatures varied by vehicle type. Side and front-end loaders met the engine exhaust temperature requirements in the greatest number of cases with approximately 50-90% achieving the required regeneration temperatures. Only 8-25% of the rear loader and roll-off collection vehicles met the engine exhaust temperature requirements. Solid waste collection vehicles represent a diverse fleet with a variety of duty cycles. Low engine exhaust temperatures will need to be addressed for successful use of passive DPFs in this application.