INTRODUCTION 



Tins report is a summary of the activities of 

 the Committee on Propagation, NDRC. It is 



divided into three parts, each of which deals with a 

 particular type of activity or record. 



Part I is an account of the administrative activities 

 of the Committee, its origin, organization, and work, 

 with a description of the needs of the armed forces 

 which called it into being. It is divided into four 

 chapters for convenient reference. In general, the 

 technical aspects of the problems set before the 

 Committee, and of the work undertaken to solve 

 those problems, are touched on in Part I only suffi- 

 ciently to make clear the needs of the Services and 

 the steps taken to satisfy those needs. Actual 

 chronology is adhered to as far as possible with any 

 departures indicated where they occur. This part of 

 the report is designed to serve not only as a record 

 of the Committee's work but to assist any future 

 group in the organization of a similar program, 

 should the occasion arise. Chapters 1 and 2 describe 

 the organizational setup, liaison channels, objectives, 

 the changes which occurred, and the reasons for 

 making them. Chapter 3 relates the chronological 

 activities of the organization. Chapter 4 summarizes 

 the results accomplished and also contains a critique 

 of the organization and its work, as evaluated by the 

 chairman, with recommendations for future investi- 

 gation in this field. 



Part II is a technical description of the develop- 

 ment of propagation work during W)rld Wir II and 

 the results obtained by the various organizations 

 engaged in this work. Chapter 5 begins with a defi- 

 nition of certain basic concepts and proceeds with a 

 review of so-called standard propagation as known 

 at the beginning of the war. For a rapid survey 

 of the vast body of information that has since been 

 acquired, Chapter 6 reviews nonstandard propaga- 

 tion from an elementary theoretical viewpoint. The 

 principal discovery made during the war is that the 

 effective range of radar and short-wave radio equip- 

 ment depends essentially and critically on the 

 distribution of the refractive index in the lower 

 strata of the atmosphere. In Chapter 7 the newly 

 developed methods for the measurement of the 

 refractive index variation are described, and a collec- 

 tion of typical refractive index curves resulting from 

 actual measurements in various parts of the world 

 is presented. 



Chapter 8, the central chapter of Part II, gives a 

 brief chronological record and the principal results of 



the major propagation experiments performed in 

 Great Britain, Canada, and the United States. 

 Because short and microwave propagation charac- 

 teristics are determined by the physicial condition 

 of the lower atmosphere, they are intimately 

 connected with the evolution of the weather on a 

 large scale as studied by the forecasting meteorolo- 

 gist. The relationships between the dynamics of 

 the air and the distribution of refractive index are 

 presented in Chapter 9. A review of the climatic 

 and seasonal conditions involved in various parts of 

 the world and of the bearing of all these factors upon 

 the forecasting of radio propagation conditions is 

 included. Finally, in Chapter 10, the results of 

 investigations on the atmospheric absorption of 

 microwaves and of the scattering of short and 

 microwaves by radar targets and by raindrops are 

 summarized. 



The data given in this report refer only to the 

 transmission of the higher frequency bands, above 

 about 30 mc. 



Parts III and IV are devoted to the presentation of 

 18 reports, out of 61 published in the Summary 

 Technical Report, which were presented before the 

 second, third and fourth conferences on propagation 

 held in February, 1944, November 1944, and May 

 1945, or were published by the Columbia University 

 Wave Propagation Group. Those appearing in Chap- 

 ters 11 through 15 are concerned with standard 

 propagation; Chapters 16 through 27 with nonstand- 

 ard propagation. The remaining 43 reports are pub- 

 lished in Volume 2. 



One of the main functions of the Committee was 

 to bring about a rapid exchange of information 

 between the laboratories and Service units working 

 on the subject, thus making the results available to 

 all workers technically concerned with the military 

 application of radar and other short wave radio 

 equipment. To fulfill this function the Columbia 

 University W ive Propagation Group operating under 

 contract with the Committee periodically published 

 a comprehensive bibliography on propagation, begin- 

 ning in the spring of 1944. Its fifth and last edition, 

 issued in August 1945, is included in this volume. 

 This bibliography is a rather exhaustive documenta- 

 tion of the efforts made during the war in this field 

 by Great Britain, Canada, New Zealand, Australia, 

 and the United States. Reference to papers and 

 reports is made in the main body of this summary 

 by superior numbers. 



