Prof. Attwood was appointed Director of the Columbia University Wave Propagation Group [CUDWR WPG] which operated under contract OEMsr-1207, to integrate, analyze, and disseminate reports of research. This contract went into force on November 1, 1943.

Dr. Burrows, Prof. Attwood, and D. E. Kerr flew to England November 22, 1943, to confer with British. investigators and secure integration of the United States and British programs. As a result of this visit, a unified program of research was agreed upon, with certain divisions of effort to prevent duplication of particular phases of the work, and to insure covering all practical aspects of the problem. The British agreed to continue experiments on wavelengths of 9, 6, and 3 cm, with parallel measurements of meteorological factors, and also to undertake measurements at 1.25 cm when equipment became available. The effects of hills and trees on the shorter wavelengths was also to be studied. They were also to continue theoretical investigations already under way with special emphasis on use of the Manchester University differential analyzer.

It was agreed that American agencies would make detailed measurements to determine the characteristics of water vapor diffusion in a warm air mass blowing over cold water, with accompanying radio transmission tests at wavelengths of roughly 10 and 50 cm. A team of research workers was to be organized and equipped to make simultaneous propagation and meteorological measurements at locations providing conditions similar to those encountered by radar-using personnel of the armed forces. Tests on 1.25-cm waves were to be made along the eastern coast of the United States as apparatus permitted, to provide data on propagation conditions typical of the eastern coast of a large continent.

It was agreed also that Dr. John E. Freehafer of MIT-RL would be sent to Britain in order to obtain closer cooperation in theoretical attacks being made on these problems.

It was further agreed to make a study of atmospheric absorption, particularly at 3-cm and shorter wavelengths, and of absorption by rain, fog, dust, and other such phenomena. The reflection coefficient of the sea for radiation of 10-cm and possibly 3-cm and shorter wavelengths was to be studied for grazing angles less than 5 degrees, and the back-scattering effect was also to be investigated. Storm echoes and their possible tactical uses were also to be treated. In addition, the United States was to set up

and maintain a group to compile, analyze, integrate, and disseminate propagation information.

It was jointly agreed to interchange samples of meteorological instruments most useful for measurements in connection with propagation studies.

Upon return to the United States of this mission, in January 1944, offices were occupied in the Empire State Building, New York City, jointly with the Wave Propagation Group of Columbia University Division of War Research.

On February 12, 1944, a meeting was held at which liaison representatives from the armed forces presented certain urgent Service requirements and outlined experimental programs that the respective branches were prepared to undertake in cooperation with the Committee.

One of the most urgent needs in the Services was for a handbook and other instructional aids, prepared in the simplest practicable form for the use of operational personnel with limited technical background. It was proposed that the Columbia University Wave Propagation Group, which had been set up in accord with the program agreed on with the British, should undertake the preparation of such aids to instruction. At a meeting held February 15, 1944, a statement outlining the propagation problem was drawn up, with proposals for Service cooperation in experiments devised to provide solutions to the most urgent aspects of the question. This statement set forth the NDRC Committee's view that the problem of "nonionospheric propagation in a nonstandard atmosphere" should be given highest priority, and it gave details of experiments proposed or already under way. Five specific experiments were outlined, in each of which the assistance of the Services was required. These were as follows:

1. Organization and equipment of a complete transportable field unit for conducting propagation experiments, which could be sent to any region considered likely to yield results useful in the operational theaters. This experiment would require considerable apparatus and a team of trained research, operational, and maintenance personnel. Dr. Paul Anderson of the State College of Washington provided a considerable amount of material on this project.

2. An over-water experiment along a path between Cape Ann and Cape Cod was to be carried out by MIT-RL, to obtain information on propagation characteristics along the eastern coast of a continent. These data would be applicable to similar regions in

war theaters, particularly near the Chinese northeast coast.

3. A detailed experiment was considered desirable in a region where stable temperature inversions were produced in the atmosphere by subsidence of upper layers of air. Such experiments were already being conducted by the U. S. Navy Radio and Sound Laboratory [NRSL] along several over-water paths near San Diego, California.

4. An experiment near the Panama Canal Zone was planned by the Navy in cooperation with the State College of Washington group under Anderson, to establish a correlation between meteorological conditions of that region and radar performance. It was expected that this would provide a good test of equipment and methods under tropical conditions and that the information obtained would apply in other similar regions.

5. An experiment was proposed to be conducted in Florida, with the aid of Signal Corps and Air Force personnel utilizing equipment already in the area. It was expected that this project would yield considerable information on means of predicting propagation characteristics for localities climatically similar.

Meantime the Columbia University Division of War Research Wave Propagation Group [CUDWR WPG], directed by Prof. Attwood and operating under contract OEMsr-1207, was preparing a report on tropospheric propagation for radar operators, officers, and other operating personnel, at the request of the Combined Communications Board [CCB] and Combined Meteorological Committee [CMC]. This report, compiled from all established data on variations in radar coverage available, was prepared in as nontechnical and popular a style as possible. It received the approval of the Wave Propagation Committee of the CCB, and about 30,000 copies were distributed to the armed forces of the United Nations during June 1944 under the title Variations in Radar Coverage (JANP-101). This report helped to clarify the problem of nonstandard propagation for Service personnel and to throw light on certain peculiarities in radar performance and coverage variations caused by newly discovered meteorological conditions (see Chapter 16). During early 1944, a bibliography of publications on propagation was prepared and published by the CUDWR WPG.

At a meeting on February 28, 1944, a direct request from General MacArthur to NDRC was laid before the Committee, which asked that a group of scien

tists be sent to Australia to study radar and communication problems in that area of the Pacific theater. It was finally arranged that the communication part of this request would be handled by the Signal Corps and that the radar portion would be fitted. into the general research program already in process of organization.

Out of the series of meetings and conferences held during February, a program of four principal points was developed which was presented on March 4, 1944, to the Wave Propagation Committee of the Joint Communications Board. This program was accepted and put into effect soon afterward, as follows.

1. A working group under the direction of Dr. Anderson proceeded to the Canal Zone to conduct. meteorological measurements in cooperation with the Navy. Following completion of this work, the group proceeded to Australia and performed similar investigations as requested by General MacArthur. This work was carried on under contract OEMsr-728, with the State College of Washington. Arrangements were also made for training a group of about 20 Army and Navy officers in use of the meteorological measurement technique and apparatus developed by Dr. Anderson. These officers were later to be sent into the field to organize teams for making meteorological soundings.

2. The Wave Propagation Group of the MIT-RL under D. E. Kerr conducted a study along an overwater path on the east coast of the United States, as outlined previously.

3. The NRSL investigation of propagation under subsidence conditions was continued.

4. Propagation conditions over land were planned for study by Canadian Army research groups. Preliminary discussions were held with these groups early in 1944.

On March 13, Dr. Burrows and Prof. Attwood conferred with the staff of the NRSL in San Diego in connection with the investigation of propagation under subsidence conditions. The research was integrated into the general program and reported to the Joint Communications Board [JCB] on March 29.

As a result of this visit the NRSL agreed to modify and expand its propagation research extensively to include tests over a number of different paths, using both one-way and radar transmissions, with simultaneous meteorological measurements. These experiments were to be measurements of propagation on three representative frequencies along a 108-mile

over-water path between Los Angeles and San Diego, and comparable frequencies between San Diego and San Pedro, a distance of 80 miles over water, using suitable antenna heights. Atmospheric soundings were to be taken from a ship at a point midway along such paths and also on shore as near the midpoint as possible. Measurements with a blimp to determine the extent of uniformity of the inversion layer were also projected.

Measurements were to continue on fixed radar targets located at various altitudes and along various azimuthal bearings. Field strength measurements were also to be made from an aircraft flown at significant altitudes over the transmission paths, the results to be correlated with meteorological data. The chairman assisted inauguration of this expanded program by using the Committee's powers and influence in obtaining additional apparatus required. In addition, information was exchanged with members of a British scientific delegation who were present, and considerable effort was directed to obtaining a meteorologist for full-time work with the NRSL group conducting the experiment.

On April 3, Dr. Burrows, Comdr. J. L. Reinartz, and Lt. Comdr. D. H. Menzel visited Panama to observe the experiments being conducted jointly by Dr. Anderson's group and the Navy.

As a result of this visit, substantially better and more extensive cooperation between the scientific. group and Service forces in the area was obtained, and an analysis of the data obtained to date was secured, which revealed occurrence of a predictable surface duct condition.

A conference was held in Washington on May 2, 1944, at which representatives of the various research agencies of the United States interested in propagation were present. A large amount of propagation information was exchanged by presentation of many papers describing various experimental and theoretical researches going on in various countries. The complete record of papers and proceedings was published by the CUDWR WPG and is contained in the Bibliography at the end of this volume.

Special consideration was given to the question of symbols and nomenclature by a committee headed by Prof. Attwood. A list of such symbols was prepared by this committee and was accepted without dissent by the Wave Propagation Committee of the CCB on May 17, 1944.

On May 23 the chairman of the Committee on Propagation presented to the NDRC a report on

what had been accomplished up to that time by the Committee and its plans for the ensuing year, together with budget requirements. The budget was approved with minor deletions in the items covering contingencies.

On June 29, 1944, a meeting was held at which the progress of the various experimental projects was reviewed in some detail. Two Armed Service requests were also taken up. The first, submitted by Comdr. Menzel and Dr. T. J. Carroll, dated June 12, 1944, outlined the general needs of the Services. Copies of this letter were forwarded to the Committee members for their consideration before the meeting convened. The second was received from General Colton, in the Office of the Chief Signal Officer, and specifically requested a theoretical investigation of the effects of low-level tropospheric layers on propagation at wavelengths near 10 and 3 cm.

After discussing specific requirements of the services as laid down in the Menzel-Carroll letter, certain of the questions were referred to appropriate agencies for solution. In particular, MIT-RL undertook to study the effects of refraction on gunfire control radars operating in the 10- and 3-cm bands. Most of the other questions raised were already under investigation but were not yet sufficiently advanced to permit of conclusive answers. General Colton's request was considered to be covered by the action taken in connection with the Menzel-Carroll letter.

In addition to progress reports from United States research agencies, a report on British work was submitted, particularly on the status of 9-6-3-cm experiments over the Irish Sea. Little useful correlation between propagation and meteorological factors had yet been obtained in this experiment. Projected British experiments included investigation of absorption and attenuation of 10- and 3-cm band radiation. in oxygen, in water in all forms occurring in the atmosphere, and in salt spray.

Late in June 1944, the need for closer liaison between the Committee and CMC was met by the appointment of Major H. Wexler of the Army Air Forces, Weather Division, as a technical advisor. This also strengthened the meteorological representation associated with the Committee, which had not formerly been completely adequate.

The Committee met at the Radiation Laboratory on August 4, 1944. During this meeting plans were laid for an extensive conference on propagation to be held in Washington, D. C., on November 16 and 17, at which representatives of research agencies in

all the countries engaging in propagation research could present findings to date.

Plans were laid for Dr. Anderson's trip to the Southwest Pacific theater in response to General MacArthur's request for investigation of propagation phenomena. This project was of considerable importance and is more fully described elsewhere in this report.

A report by Dr. Svein Rosseland, assistant to Prof. Attwood in the CUDWR WPG, was heard, on work going on in England and on data brought back to that country by Dr. Booker. These data described radar echoes from points more than 1,500 miles from the 200-me Bombay, India, station, which had been observed during the season following the northeast monsoon.

Other reports were heard on Bell Telephone Laboratories [BTL] experiments on K band along a path to Atlantic Highlands and similar experiments by MIT-RL near Boston. No nonstandard propagation had been observed at Atlantic Highlands, but some had occurred in the Boston area.

Experiments of MIT-RL along a ten mile path had indicated the impossibility of measuring the effect of oxygen and water vapor outside the laboratory itself.

Dr. W. H. Furry described the work of preparing coverage diagrams for radar and VHF (very high frequency) communication equipment under groundbased duct conditions. Owing to the volume of calculations required in this work it was decided to obtain use of the Harvard University automatic sequence-controlled calculating machine, which would effect a probable reduction in the time required from an estimated nine or ten months to about three weeks. This proposal was subsequently carried out.

Dr. Beverage presented certain problems of Division 13, particularly the need for supplying the best. information on probable coverage to signal officers in the field at the earliest possible date. Estimates based on the 43 earth radius formula tended to be pessimistic.

Dr. H. Goldstein presented information on the problem of fluctuating signals. Instability in the equipment was a source of great difficulty, but, when this had been overcome, such results as were obtained indicated that most fluctuation was due to interference.

Plans were made for a field trip to observe the extensive MIT-RL experiments proceeding on four different wave bands along a path between Race

Point and Gloucester. On this trip the entire apparatus and organization of the experiment were inspected and discussed.

A detailed memorandum of the Committee's current work was submitted on August 10 to the Chiefs of NDRC Divisions 13, 14, and 15, in order to keep these groups informed of developments. The breakdown of activities described five well-controlled experiments which were under way in different meteorological environments and the theoretical attack proceeding in Britain and the United States. These experimental attacks on the problem have been described earlier in outlining the Committee's program for the year. The memorandum referred to here specifically invited Division comment on the program in progress and requests for other investigations if additional ones seemed desirable.

A Committee meeting on September 21, 1944 considered new humidity measuring instruments and reviewed progress of the work under way at RL. This was reported by D. E. Kerr as nearing the conclusion of the experimental work. The matter of educational films to disseminate propagation information to the Services was brought up, and the need for a technical aide to the Committee who should be familiar with NDRC procedure was discussed. Dr. Burrows stated that efforts were being made to obtain a contractor who would make meteorological measurements along the BTL to Mt. Neshanic propagation path, for correlation with the transmission data available at BTL. These measurements were later undertaken by the Airborne Instruments Laboratory [AIL] of Mineola, Long Island. The matter of eventual demobilization of OSRD was discussed, particularly as to effects of such demobilization on investigations of propagation then in progress.

The Committee met again on November 15, 1944 to consider replies received from Divisions 13, 14, and 15 to the memorandum outlining its program in progress submitted on August 10 and to transact other business. The matters of calculation of radar coverage diagrams for nonstandard conditions, of the range and reliability of very high frequency [VHF] and ultra high frequency [UHF] communications links, and the choice of frequencies for such links were taken up in detail. After thorough consideration, a reply was drafted for the Divisions concerned, particularly Division 13, stating that available information on propagation did not permit preparation of accurate coverage diagrams for such communications circuits on any other basis than

that of 43 earth radius, as was already being done. It was expected that work then in progress would modify the limitation as it progressed. In the matter of choice of VHF, UHF, and super high frequencies [SHF], information was not yet available, but surveys under way were expected to provide some background, although the intricacy of the problem did not encourage hope of an early complete solution.

The difficulties involved in the preparation of field strength contours appeared so formidable that requests from the Services for preparation of such contours was withdrawn, and a new request was substituted. This asked that workers on theoretical or observational and experimental programs forward as informal memoranda such examples of correlations between meteorological conditions and propagation characteristics as could be applied directly in the field, with suggestions for possible tactical applications. This substitute request was received by the Committee in November.

In addition, an important report by Dr. Anderson from the Southwest Pacific theater was considered which described the progress of project PDRC-647 which members of the State College of Washington staff had undertaken under Contract OEMsr-728. Its objectives were to explore meteorological conditions in the Southwest Pacific theater to determine their effects on propagation, and to assist the Army in establishing a forecasting service for the tactical exploitation of nonstandard propagation in that region.

After several conferences between Dr. Anderson's group, various Australian agencies, and representatives of the Air Signal Office, Far East Air Force [FEAF], headquarters for the mission was established at the Radio Physics Laboratory at Sydney. Meetings were held here with Professor F. W. G. White and representatives of the Royal Australian Air Force and Royal Australian Navy. The following facts were brought out. The Australian and NDRC programs supplemented each other without duplication of effort, making revision of plans unnecessary. An acute need existed for definite information concerning low-level meteorological conditions in the oceanic areas of the Southwest and Central Pacific. This information could best be obtained by NDRC and United States Army groups.

Rough forecasting of nonstandard propagation along the southeast, south and southwest coasts of Australia was possible, correlating superrefraction

data collected from radar stations with synoptic meteorological data.

Observations from North Australia showed no similar clearcut correlations. Reports from New Guinea and the Solomon Islands were too meager to be useful.

A Radio Physics Laboratory [RPL] experimental program was projected at a location near Darwin, Australia, which would be correlated with land, shipbased, and aircraft soundings and synoptic weather. A low-level sounding equipment was delivered to RPL for use in these experiments.

A conference was held at the Radio Development Laboratory in New Zealand at which a low-level sounding equipment was delivered and trial soundings taken by Dr. Anderson. As a result of this meeting, a long-range program was agreed on in addition to the work already being conducted by New Zealand agencies. This program would take advantage of the unusual conditions offered by the persistent Föhn winds which override the cold water at the eastern coast.

Dr. Stephenson of Dr. Anderson's group began the collection of meteorological and oceanographic data available in Australia preliminary to the selection of optimum sites for radar-weather observations. New information was available on continental and general equatorial meteorology but very little for the ocean area to the west and north of New Guinea.

Recommendations for establishment of a limited number of radar-weather stations in the Biak-OwiNoemfoor region were submitted to the FEAF late in August. These recommendations were approved after some discussion, but the plans were changed when FEAF headquarters suggested the usefulness of an Army radar-weather team with sounding equipment in the projected operations at Leyte. Preparations were made to take advantage of this suggestion.

Consideration was given to determination of the low-level conditions characteristic of the Southwest and Central Pacific oceanic areas, with tentative conclusions from data secured during the summer of 1944 that strong ducts to 40 or 50 ft and weaker stratifications to 800 or 1,000 ft were common in the region, especially in late afternoon. In the doldrum region standard conditions were the rule. The need for more complete measurements was pointed out, and the use of PT boats and seaplanes to obtain them was secured.

Approval for measurements in the region near