December 17, 1920] 



SCIENCE 



575 



Bible use of aerial photographs in connection 

 with hydrogi'aphic surveys. The primary ob- 

 ject in view was the elimination of wire drag 

 work, especially in the clear water of the 

 Florida coast. An attempt was made to pho- 

 tograph small coral heads and pinnacle rocks, 

 as it is the existence of these needle-like 

 dangers to navigation that require the use 

 of a wire drag. The equipment at the Air 

 Station at Key "West was limited, but thor- 

 ough tests were made with that available. 

 Various types of cameras were used, as well 

 as different combinations of filters and plate 

 emulsions. Photographs were made at alti- 

 tudes of from 200 feet up to 4,000 feet, and 

 under various light conditions. It was hoped 

 that some combination of the various factors 

 involved would produce satisfactory results. 



The problem of control was solved, by in- 

 cluding in each photograph, two vessels of the 

 survey. The photographs could not be cor- 

 rected for tilt with only two known points as 

 a base, but the control as furnished by the 

 positions of the two vessels, was found to be 

 sufficient for the experiments. 



A well-surveyed area near Key West was 

 chosen, and the vessels proceeded on parallel 

 courses over this area at full speed, the plane 

 flying forth and back above the course. The 

 courses and positions of the vessels were 

 recorded as in ordinary soimding work. The 

 photographer in the plane recorded the exact 

 time that each exposure was made, with other 

 data such as altitude, exiwsure, plate, filter, 

 etc. Each photograph was later oriented by 

 plotting the positions of the vessels on the 

 chart at the instant the exposure was made. 



These experiments proved very conclusively 

 that photographs from the air, using present 

 day equipment, are of little practical value to 

 the hydrographer. When any of the under- 

 water features did appear in the photographs, 

 contrast in color was the most prominent, 

 with no indication as to whether the contrast 

 indicated shoal or deep water. Vari-colored 

 bottom, of uniform depth, appears in the 

 photograph as apparent difference in depth. 

 Many charted shoals are not indicated in the 

 photographs, while adjacent ones show clearly. 



Taken altogether, the results are so uncertain, 

 that the chances of eliminating field work in 

 hydrography are very remote. Developments 

 in the art of photography may change this 

 viewpoint. 



REVISION OF THE COAST OF NEW JERSEY 



In March, 1920, the Army Air Service pho- 

 tographed the coast line of New Jersey from 

 Cape May to Seabright. A single flight was 

 made using the K-1 camera. The plane flew 

 at an altitude of 10,000 feet, and under 

 very good air conditions. The camera was 

 mounted in gimbals, with a lead weight at 

 the lowest point to assist in maintaining the 

 optical axis of the camera in a vertical 

 position. Level bubbles were placed on the 

 camera, to aid in keeping the camera in the 

 proper position. This is the most satisfac- 

 tory way to suspend the camera, and control 

 its verticality, at the present time. The pho- 

 tographs are being used for a revision of the 

 charts of the coast of New Jersey. The in- 

 dividual photographs are 18 X 24 cm. in size, 

 and the approximate scale is 1 :10,000. The 

 photographs are mounted in strip mosaics, 

 for convenience sake, not over four feet in 

 length. The length is generally determined 

 by the position of control points. This com- 

 ■ posite photograph is compared with the 

 topographic sheet of the same area, and con- 

 trol points identified. The scale of the photo- 

 gi'aphic mosaic is determined, and by means 

 of the pantograph, the data are reduced to the 

 scale of the chart, and transferred from the 

 photographs to tracing paper. 



The photographing of this 120 miles of 

 coast line took less than two hours time in an 

 ail-plane. The development of the films and 

 printing took two days time of one man. Two 

 rolls of film were used, a total of 183 photo- 

 graphs. The work of interpreting the photo- 

 graphs, assembling mosaics, comparison with 

 topographic sheets, and reduction to the scale 

 of the chart of the outside shore line required 

 15 days of office work by one engineer. 



E. Lester Jones 

 TJ. S. Coast and Geodetic Stibvey 



