This handbook is a comprehensive collection of data, formulas, definitions, and theories concerning the natural environment. It was written by scientists of the Air Force Cambridge Research Laboratories (AFCRL) which, in 1976, became the Air Force Geophysics Laboratory (AFGL). It was designed to serve a broad spectrum of users: the planner, designer, developer, and operator of aerospace systems; the scientist who will find the tables and figures a convenient reference in his own field; the specialist who needs environmental data in another discipline; and science minded people who seek a summary of space-age environmental research. Revisions of individual chapters and sections of this handbook will be published as additional environmental research efforts pay off in new knowledge.