February issue includes Appendix entitled Directory of United States Government periodicals and subscription publications; September issue includes List of depository libraries; June and December issues include semiannual index.

This book is about spaceborne missions and instruments. In addition, surveys of airborne missions and of campaigns can be found on the accompanying CD-ROM in pdf-format. Compared with the 3rd edition the spaceborne part grew from about 300 to 1000 pages. The complete text - including the electronic-only chapters - contains more than 1900 pages. New chapters treat the history of Earth observation and university missions. The number of commercial Earth imaging missions has grown significantly. A chapter contains reference data and definitions. Extensive appendices provide a comprehensive glossary, acronyms and abbreviations and an index of sensors. An effort has been made to present the information in context, to point out relationships and interconnections. The book may serve as a reference and guide to all involved in the various national and international space programs: researchers and managers, service providers and data users, teachers and students.