Flight Planning For Oblique Sfap

Flight planning for oblique aerial photography is rarely done to achieve overlapping images for mosaics or stereoimagery, as detailed in previous sections. Rather the oblique vantage is chosen to depict the spatial relationships of objects and features within the landscape in a more pictorial fashion. The geometric distortions of single-point perspective, relief displacement, and scale variations are accepted, and the

FIGURE 9-17 High-oblique view northward over the Elk River Wind Farm in the Flint Hills of south-central Kansas, United States. Each tower is 262 feet (~80 m) tall and blades are 125 feet (~38 m) long. Kite aerial photography with the kite positioned upwind from the turbines (note positions of blades) and camera ~ 120 m above ground. Long shadows show the sun position in this late autumn afternoon view. Photo by JSA and SWA, November 2009.

FIGURE 9-17 High-oblique view northward over the Elk River Wind Farm in the Flint Hills of south-central Kansas, United States. Each tower is 262 feet (~80 m) tall and blades are 125 feet (~38 m) long. Kite aerial photography with the kite positioned upwind from the turbines (note positions of blades) and camera ~ 120 m above ground. Long shadows show the sun position in this late autumn afternoon view. Photo by JSA and SWA, November 2009.

emphasis is given to best lighting, shadow placement, tilt angle, and other factors that impact the visual scene. In general, views looking away from the sun without excessive shadowing and without the hot spot are preferred (see Chapter 4).

The type of flying platform, terrain conditions, wind direction, and other factors influence what type of oblique imagery may be acquired under favorable conditions. Consider, for example, the challenge of acquiring aerial photographs of huge turbines in a wind-energy farm. Individual turbines typically stand 90-120 m tall, and they are arrayed in fields with many dozens spaced a few 100 m apart. In vertical view, the turbines may be almost impossible to see; the towers have small "footprints" looking straight down. Their shadows may be distinct, depending on lighting conditions, and they may appear in side profile toward the edges of vertical photographs because of relief displacement. Nonetheless, oblique views might well be more desirable (see Fig. 10-24).

Flying any type of manned aircraft in close proximity to such turbines would be at least foolhardy, in view of turbulent wind currents, if not prohibited. Various types of unmanned SFAP platforms could be positioned for overviews and closeup oblique images. Tethered platforms would give the greatest control from the ground. Balloons and blimps would be safe only under calm to light wind (turbines not operating), which leaves kites as the safest platform when turbines are in motion (Figs. 9-17 and 9-18). Ideally the kite should be positioned well upwind or downwind from the turbines with the sun behind the camera, but such arrangement may not be possible depending on ground access. A free-flying unmanned platform would be subject to the same turbulent wind currents, which definitely would require a human pilot to control the aircraft. Flight planning should include considerable flexibility and quick response under these conditions.

FIGURE 9-18 Close-up view of wind turbines at the Spearville Wind Energy Facility, southwestern Kansas, United States. The tip of the upright blade of the near turbine is ~390feet (120 m) above the ground. The camera is positioned ~ 250 feet (75 m) high for this side view of the turbines. View toward the north; kite aerial photo by SWA and JSA, November 2008.

FIGURE 9-18 Close-up view of wind turbines at the Spearville Wind Energy Facility, southwestern Kansas, United States. The tip of the upright blade of the near turbine is ~390feet (120 m) above the ground. The camera is positioned ~ 250 feet (75 m) high for this side view of the turbines. View toward the north; kite aerial photo by SWA and JSA, November 2008.

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