PREFACE 



ONE OF THE important contributions of the NDRC 

 Comnuttee on Propagation of permanent value is 

 the publication of the teclmical papers presented at 

 the several Conferences on Propagation, and the pub- 

 lication of documents prepared for the Committee 

 under contract OEMsr-1207 by the Columbia Univer- 

 sity Wave Propagation Group. 



The first Conference was held at the Radiation 

 Laboratory at Massachusetts Institute of Technology 

 in July 1943 prior to the formation of the Committee 

 on Propagation. Those sponsored by the Committee 

 were the 2nd, 3rd and 4th Conferences held, respec- 

 tively, in New York, February 1944; in Washington, 

 November 1944; and in Washington, May 1945. 



The bulk of the material published is taken from 

 the Columbia University reports and from the papers 

 presented at the 3rd and 4th Conferences; the re- 

 mainder comes from the 2nd conference. By careful 

 selection it has been possible to avoid excessive repeti- 

 tion ; and yet on continuing projects, such as trans- 

 mission studies, it is possible to follow their develop- 

 ment over a considerable period of time. 



Some of the material has been pviblished in Volume 

 1 of this series — that dealing with the theoretical as- 

 pects of propagation, both standard and nonstandard. 

 In this volume the reader first finds, in Part I, a sum- 

 marizing review of six transmission experiments car- 

 ried out in widely separted geograpliical locations : 

 namely, Massachusetts Bay, San Diego, Arizona, An- 

 tigua, West Indies, and Great Britain. The basic 

 objectives here have been to learn the facts concerning 

 transmission and, as far as possible, to correlate them 

 with the transmission theory given in Volume 1 and 

 with the meteorological factors presented in this 

 volume. 



In Part II of this volume the subject considered is 

 meteorology : first theory, then equipment, and finally 



the development of forecasting techniques in which the 

 ultimate goal is the ability to predict radio perform- 

 ance from meteorological measurements made consid- 

 erably earlier. 



In Part III, Chapter 9, on reflection coefficients, 

 presents a certain amount of new material which, how- 

 ever, tends to confirm previous views and further sub- 

 stantiates formulas already available. 



In Chapter 10, on dielectric constant, absorption, 

 and scattering, the reader will find a considerable 

 volume of new material. With increasing frequency 

 the absorption by the components of the atmosphere 

 becomes increasingly important while the problems of 

 absorption and scattering, as related to frequency and 

 water droplet size, bear importantly on the ability to 

 track clouds and storms by radar. This problem, storm 

 detection (Chapter II), was interestingly presented 

 by Canadian scientists in the form of a movie of the 

 PPI of a radar tracking snow and thunder storms. 

 The written report must necessarily be less complete. 



In Chapter 12, on echoes and targets, the reader 

 will find an interesting treatment of some of the more 

 unusual problems concerning the radar behavior of 

 targets. Volume 2 closes with a consideration of an 

 angle-of-arrival experiment. 



Space limitations have made it impossible to include 

 a few reports, but these, together with numerous sup- 

 porting documents listed in the Columbia University 

 Wave Propagation Group bibliography, have been 

 microfilmed. 



Acknowledgment is due to the many authors who 

 have contributed to this series, not only for the mate- 

 rial and its oral presentation at the Conferences, but 

 also for their willingness to prepare the material in 

 form for permanent record. 



Stephen S. Attwood 

 Editor 



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