Propagation factor errors due to the assumption of lateral homogeneity

Abstract

Abstract. Propagation conditions are frequently assessed by making a single measurement of the vertical refractivity and injecting this profile into a propagation model from which the two-dimensional propagation factor field is calculated. Such an assessment tacitly assumes lateral homogeneity of the refractivity environment. That is, the refractive index is assumed to vary only as a function of height above the Earth's surface. Hitherto, the authors, using only case studies, have determined errors in propagation assessment employing the above assumptions. The objective of this paper is to characterize the errors in the propagation factor field using a statistical database of multiple arrays of refractivity profiles covering many days. In this effort, errors in the propagation factor field at 1, 3, and 10 GHz are derived for the case in which single refractive index profile measurements are used to calculate the two-dimensional propagation factor field. This "error" field is subsequently compared with the "benchmark" or "truth" propagation factor field calculated using an array of refractivity profiles. The errors are statistically deduced by combining measurements from 30 days over defined two-dimensional areas. The methodology for which the above type of propagation assessment is addressed may also be used to establish temporal and lateral spacing requirements employing similar statistical databases. IntroductionPropagation assessment in coastal regions is an important requirement for predicting radar and communications capabilities. Although propagation assessment can be accurately achieved through a measurement of the two-dimensional refractivity environment, such a measurement is frequently impractical. On the other hand, coastal and shipboard measurements of individual refractivity profiles are common through the use of balloon and rockets carrying meteorological sensors. Using a single refractivity profile and the assumption of lateral homogeneity, the propagation environment is normally assessed by injecting it into a propagation model, which calculates the two-dimensional propagation factor field. Important questions associated with this procedure are, What are the errors introduced by the assumption of lateral homogeneity of the refractivity environment?, and What are the errors introduced assuming a "standard atmosphere" refractivity profile? We address the above questions in the effort described here.Copyright 1998 by the American Geophysical Union. Paper number 97RS03321.0048-6604/98/97RS-03321 $11.00The authors have previously reported on errors in the two-dimensional propagation factor field calculated from measurements of a single refractive index vertical profile assuming lateral homogeneity of the refractivity environment [Goldhirsh and Dockery, 1995, 1996; Dockery and Goldhirsh, 1995]. These previous efforts were anecdotal, as they pertained to only a few preselected sets of profiles. Nevertheless, the previous results demonstrated the level of potential errors that may arise. We extend here t...

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