tailieunhanh - Statistical Tools for Environmental Quality Measurement - Chapter 7

Các công cụ để phân tích dữ liệu không gian Chỉ có một điều có thể được coi là thể hiện hành vi ngẫu nhiên trong việc thực hiện một đánh giá trang web. Điều đó xuất phát từ giả định thông qua giám định có nguy cơ tiếp xúc là ngẫu nhiên. Theo kinh nghiệm của tác giả không có gì là sẽ hỗ trợ một giả định của một phân phối ngẫu nhiên của nồng độ chất gây ô nhiễm cao tại trang web bất kỳ. Mà trái lại, thường có nhiều bằng chứng hợp lý hỗ trợ sự. | C H A P T E R 7 Tools for the Analysis of Spatial Data There is only one thing that can be considered to exhibit random behavior in making a site assessment. That arises from the assumption adopted by risk assessors that exposure is random. In the author s experience there is nothing that would support an assumption of a random distribution of elevated contaminant concentration at any site. Quite the contrary there is usually ample evidence to logically support the presence of correlated concentrations as a function of the measurement location. This speaks contrary to the usual assumption of a probabilistic model underlying site measurement results. Isaaks and Srivastava 1989 capture the situation as follows In a probabilistic model the available sample data are viewed as the result of some random process. From the outset it should be clear that this model conflicts with reality. The processes that actually do create an ore deposit a petroleum reservoir or a hazardous waste site are certainly extremely complicated and our understanding of them may be so poor that their complexity appears as random behavior to us but this does not mean that they are random it simply means that we are ignorant. Unfortunately our ignorance does not excuse us from the difficult task of making predictions about how apparently random phenomena behave where we have not sampled them. We can reduce our ignorance if we employ statistical techniques that seek to describe and take advantage of spatial correlation rather than ignore it as a concession to statistical theory. How this is done is best described by example. The following discusses one of those very few examples in which sufficient measurement data are available to easily investigate and describe the spatial correlation. ABC Exotic Metals Inc. produced a ferrocolumbium alloy from Brazilian ore in the 1960s. The particular ore used contained thorium and slight traces of uranium as an accessory metal. A thorium-bearing slag was a .