Kenneth M. Nagler 1 cloud photography and Stanley D. Soules 2 National Weather Satellite Center from the Gemini 4 U. S. Weather Bureau spaceflight Washington, D. C.

Introduction As part of their many accomplishments in the Gemini 4 spaceflight of 3-7 June 1965, Astronauts James A. McDivitt and Edward H. White successfully carried out several sci- entific experiments. The purpose of one of these, designated S-6, was to photograph selectively and in color a variety of cloud systems. The picture on the cover is one of the intriguing scenes photographed from a height of about 100 miles. It shows con- vective cells in the central North Pacific Ocean with a few vortices along the boundaries of the cells. Cellular cloud patterns, observed in many areas of the world, are the result of weak organized convection occurring in the absence of significant vertical wind shear. They appear in a variety of sizes and types and are frequently seen in TIROS pictures (Krueger and Fritz, 1961). In the cover photograph, the larger cells are from about 20 to 40 miles in width.

The need for pictures Since there is daily meteorological satellite coverage of the greater part of the world, one from manned satellites might ask why additional photographs are desired. Obviously, TIROS satellites are con- tributing greatly to the routine surveillance of the earth's weather and, in fact, are a primary source of information on which to base forecasts for much of the world in sup- port of manned spaceflights. The TIROS pictures, however, are televised from an alti- tude of 400 miles or more. Some pictures are imperfectly understood because smaller features cannot be resolved. Therefore, for a number of selected meteorologically inter- esting cloud systems, it is desirable to have the detailed color views obtainable in actual photographs from the lower altitudes of manned spacecraft. Such pictures can amplify and verify the information obtained from weather satellites. In addition, some pictures are significant by themselves whether or not there is simultaneous meteorological satellite coverage. Another need which can be satisfied by use of manned satellites is the depiction of cloud systems at fairly short intervals of time. For example, pictures could be obtained on successive revolutions of the Gemini spacecraft to see the changes and movements of clouds at about 90-minute intervals at some points along the ground track of the spacecraft.

Past photography A number of excellent cloud photographs have already been taken by the astronauts in from space the Mercury program and in the Gemini 3, first manned Gemini flight. Good pictures also were obtained on a few of the unmanned Mercury flights. For example, the un- manned Mercury/Atlas-4 flight of 13 September 1961 provided excellent views of Hurri- cane Debbie in the mid-Atlantic Ocean and of a variety of other weather systems over the Atlantic Ocean and over Africa. Two photographic experiments were performed for one of the authors (Soules) by Astronauts Walter M. Schirra, Jr., on Mercury space- flight MA-8 and by L. Gordon Cooper, Jr., on Mercury spaceflight MA-9. The experi- ments were designed to examine some of spectral reflectance characteristics of clouds, land, and water areas of the earth's surface when viewed from outside the atmosphere. This was accomplished by taking photographs through wide bandpass color filters with a hand-held camera. On the former flight, pictures were taken on black-and-white film through six filters in the visible spectrum; on the latter flight, on infrared film through three filters.

1 Head, Spaceflight Meteorology Group. 2 Physical Meteorology Branch, Meteorological Satellite Laboratory.

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The results from these experiments confirmed that the spectral sensitivity of a television camera system on a meteorological satellite for taking pictures of the earth and clouds in reflected sunlight should be restricted to the 5000-7200 Angstrom interval. The choice of this spectral interval is a compromise between the adverse effects of scattering by mole- cules and aerosols in the atmosphere at shorter wavelengths and the low contrast between clouds and land covered by green vegetation, which is highly reflective at near infrared wavelengths. Gemini 4 photography As a result of the interest within the Weather Bureau and elsewhere, a weather photog- raphy experiment was proposed to the National Aeronautics and Space Administration for the Gemini program. The proposal was accepted for the Gemini 4, 5, 6, and 7 missions, with the authors as co-experimenters. The general intent of this experiment was, as stated earlier, to obtain selective photographs of interesting cloud systems, in color, from the approximately 100-mile altitude of the Gemini flights. The first flight on which this experiment was scheduled, that of McDivitt and White, provided a number of excep- tionally fine photographs of the earth.

Camera and film The camera that was chosen to take these pictures during the spaceflight was a modified Hasselblad, Model 500C, held by hand. It was fitted with a magazine containing 70-mm roll film perforated on both edges. A total of five film magazines was carried on the spacecraft, one of which was specifically designated for the weather photography experi- ment. Each magazine held enough film for 55 exposures. The dimensions of the image size on each frame was about 60 mm square. In order to reduce the intensity of the blue light scattered back from the atmosphere, a haze filter was fitted to the standard 80-mm f/2.8 lens. The field of view of the camera is 35 degrees. For an oblique view showing the hori- zon line of the earth, the distance along this line is about 600 miles. However, for a view where the camera was pointed directly down toward the earth, the distance repre- sented along one edge of a picture at perigee is about 75 miles. Kodak Ektachrome MS film coated on a thin Estar base was used. It has an exposure index of ASA 64. At the end of the flight the film magazines were flown from the air- craft carrier U.S.S. Wasp to the NASA Manned Spacecraft Center at Houston, Texas, for processing.

Scheduling the Well in advance of the flight, a number of meteorologists, primarily in the National photography Weather Satellite Center, were queried by the authors about the types of cloud systems they would like to see in greater detail and what particular areas of the world were of interest. Several months before the flight, the aims of the experiment were discussed in detail with the flight crew, who, incidentally, were quite perceptive to the meteorologists' needs. Approximately a dozen specific types of clouds were suggested as possibilities for viewing on their flight. These included cellular patterns, vortices in the lee of sub- tropical islands, thunderstorms, sunglint, shadows of cirrus clouds on lower cloud layers,, intertropical convergence areas, and tropical storms. Their flight plan was constructed so that the pilots could devote part of their time to cloud photography over pre-selected areas. On the day before the flight, the pilots were briefed at Cape Kennedy by one of the authors (Nagler) on several interesting features likely to be seen on their flight. This information was revised and given to them shortly before they entered the spacecraft. During the flight, areas of interest were selected periodically from weather analyses and from TIROS pictures. When operationally feasible, this information was communicated to the flight crew from the Manned Space- craft Center at Houston, Texas, in time for them to locate and photograph the clouds— provided this did not interfere with other duties. When fuel was available for changing the attitude of the spacecraft for this purpose, the pilots could search for the desired situations. Otherwise, they could take pictures only of those scenes which came into view.

Results The pilots took a total of nearly 200 70-mm color pictures, including those for the weather photography experiment, those for a terrain photography experiment, and those of gen- eral interest, such as those taken of White while outside the spacecraft. About 100 pic- tures show clouds or contain other information of meteorological interest. Views were obtained over the southern part of the United States, Africa, southern Asia, and over 523

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many ocean areas between latitudes 32.5 degrees North and South. The spacecraft trav- eled initially between a perigee height of 90 nautical miles and an apogee height of 159 nautical miles. Surface features such as highways, airfields, shipwakes, and streams are easily recog- nizable in many of the photographs, and objects on the order of 60-80 ft are resolved. Sometimes the cloud pattern associated with a weather system covered such a vast area that it was difficult to obtain a representative picture of the system. This was the case, during the flight, for Typhoons Babe and Carla in the western Pacific Ocean and Tropi- cal Storm Victoria located west of Mexico. TIROS views of Victoria showed the typical spiral cloud bands, but the astronauts reported they were not aware of the general out- line of this storm because they were too close to it. Seven photographs, including the one shown on the cover, have been selected as good examples of the many pictures that were taken. The original color transparencies, of course, reveal much more than the black-and-white illustrations reproduced here. Several views were taken showing the daytime cloud cover over Florida and the Gulf states. A view looking southwestward across southern Florida is included as Fig. 1. The absence of cumulus clouds over most of the ocean areas and over Lake Okeechobee is apparent. In the left foreground Grand Bahama Island can be seen with its cloud cover and the shallower shoal water extending northward. The cumulus and cumulonimbus clouds in the left background are over Cuba. In Fig. 2 the slender shapes of Acklins Island and Crooked Island in the Bahamas nearly enclose a lagoon whose shallow bottom reflects sunlight back into space. To the left of the picture, the reflection of the sun from the sea surface is interrupted by the tiny dark shadows of clouds, which themselves cannot be seen against the brilliantly il- luminated background. Wave patterns, actually long-period swells, are also discernible at the right of the sunglint area. The greater development of the cumulus clouds over the land is apparent. The zone of widespread cloudiness shown in Fig. 3 was found over the Pacific Ocean at about latitude 16N and longitude 178E. This picture, with cirrostratus and large areas of convective clouds, is typical of a disturbed tropical area. TIROS pictures have often shown vortices in the lee of mountainous subtropical islands; and studies of the cause and behavior of such eddies have been made (for ex- ample, Hubert and Krueger, 1962). Fig. 4 shows several of these vortices in the Canary Island region. The fine cumulus lines which delineate the eddy motion are too small to be detected on TIROS views.

FIG. 1. View looking southwest- ward across southern Florida with Grand Bahama Island in the left foreground and Cuba in the left background.

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FIG. 2. Acklins Island and Crooked Island in the Bahamas with the sun reflecting from the adjacent sea surface.

FIG. 3. A disturbed area over the tropical North Pacific Ocean.

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FIG. 4. Curving cloud lines lo- cate eddies in the atmosphere near the Canary Islands.

Fig. 5 was selected from a series of pictures that were taken between northern Baja California and central Texas as part of the terrain photography experiment to show large physiographic features of the earth for geological studies. There are two dark areas northwest of San Angelo, Texas, and south of Midland, Texas, in the picture. While the correct interpretation of this phenomenon has yet to be established, the dark areas are thought to be the result of rainshowers which have moistened the terrain and low- ered its reflectance. Alternatively, rain several days earlier may have induced vegetation to grow more rapidly and become greener and to appear darker than in the surrounding areas. The dark region in the middle of the photograph is about 10 miles wide near the left (western) side and it expands to nearly 30 miles at the North Concho River near the picture's center. Photographs such as this may be useful in studies of rainfall distribu- tion in dry regions. Information of interest to the meteorologist is also revealed by the appearance of the terrain in Fig. 6. This view of the Arabian Desert shows seif dunes, which are elongated ridges of sand sometimes extending continuously for 100 miles or more. They are typi- cally more than 200 ft in height. Those in this view are on the order of a mile apart and one-third of a mile wide. The corridors between them are normally free of sand. Seif dunes are the result of wind flow with high directional persistency for many centuries, with the dunes being oriented parallel to the wind flow.

Future plans The study of the pictures by the authors and others in the National Weather Satellite Center has just begun and will include analysis of a number of the views and comparisons with TIROS pictures. Accurate locations of many of the pictures are not yet available at this time (late June). The pictures will also be scanned to determine what additional information can be obtained from color photography. On future flights, pictures of a variety of meteorological subjects will again be sought. It was not possible for the Gemini 4 pilots to photograph the same cloud system on suc- cessive revolutions. Accordingly, the desire for such repeated views has been stressed to the crews scheduled for the next two Gemini flights. It is hoped that the study of the pictures obtained on the Gemini 4 flight and on fu- ture flights will yield new information on the behavior of the atmosphere. It is also hoped that the experience gained in this meteorological experiment, which involves co- ordination between the astronauts and a weather center while the flight is in progress, will stimulate programs of meteorological observations and experimentation in future spaceflights.

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FIG. 5. Terrain shading in cen- tral Texas, apparently caused by recent rainfall. The prominent highway in the upper left corner connects Odessa and Midland. The stream in the center of the picture is the North Concho River along San Angelo.

FIG. 6. Seif dunes in the Arabian Desert.

Acknowledgments Primary credit naturally goes to Astronauts James A. McDivitt and Edward H. White who in spite of a busy schedule managed to take a large number of excellent photo- graphs. The authors also appreciate the assistance of the many meteorologists in the National Weather Satellite Center who have contributed and are continuing to con- tribute to the experiment. Captain Robert Mercer, USAF, of the Flight Crew Support Division at the Manned Spacecraft Center was the technical monitor for the experiment. His enthusiastic sup- port and careful planning were contributing factors to the success of the experiment. Also, the cooperation of Dr. Paul Lowman of the NASA Goddard Space Flight Center, who is the experimenter for the Gemini terrain photography effort, is appreciated.

References Hubert, L. F., and A. F. Krueger, 1962: Satellite pictures of mesoscale eddies. Mon. Wea. Rev., 90, 457-463. Krueger, A. F., and S. Fritz, 1961: Cellular cloud patterns revealed by TIROS I. Tellus, 13, 1-7. 527

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