AN URBAN RADIATION OBSTRUCTION MODEL (Research Note) RANDALL S. FRANK and R. BRUCE GERDING TRW, Redondo Beach, CA, U.S.A. and PATRICIA A. O’ROURKE and WERNER H. TERJUNG Department of Geography, California State University, Northridge, CA, U.S.A. (Received in final form 1 August, 1980) Abstract. An urban street canyon radiation obstruction model has been developed. The model can describe community structure in terms of the type and dimensions of every building, block, road, park, etc. The need for massive data acquisition in regard to obstruction modeling calls for computerized algorithms, relieving the researcher of the needless tedium of hand calculations and the accompanying high degree of error and labor costs.The model program OBSTRUCT was written in FORTRAN IV for use on the IBM 3033. To facilitate changes or modifications, OBSTRUCT was written in modular form. 1. Introduction The city has an infinite number of microclimates intimately linked to the composition of its surfaces and the relationships among its structures. Microclimates created or drastically altered by the shade effects of tall buildings are one simple example. An understanding of the microclimates created by buildings should aid in the planning of new urban sites or the redevelopment of old ones. A predictive methodology is needed to deal with the fundamental processes of the varied geometries and compositions of the city’s fabric. A basic problem is to understand the spatial relationships between sunlit surfaces, shaded surfaces, and horizon obstructions. This is determined by the orientation and height of buildings, street width, solar zenith angle, and solar azimuth. Among other things, the heights of the skyline in all directions in regard to a particular surface have to be acquired. The physical nature of an urban community can be described or modeled in terms of its structural characteristics. The level of description depends on the modeling resolution employed. As a coarse indication of community structure, one might describe land use in terms of the presence or absence of man-made structures. A more refined model might describe community structure in terms of the type and dimensions of every building, road, park, railroad, etc. Studies by Terjung and Louie (1974), Outcalt (1972), Arnfield (1976), Nicholas and Lewis (1980), and Terjung and O’Rouke (1980) have shown the need for such considerations. The need for massive data acquisition in regard to obstructions calls for suitable computerized algorithms, relieving the investigator of the needless tedium of hand manipulations. Boundary-Layer Meteorology 20 (1981) 259-264. OOOS-8314/81/0202-0259$00.90. Copyright @ 1981 by D. Reidel Publishing Co., Dordrecht, Holland, and Boston, U.S.A.