. Calculate how far the camera would move during the exposure time for each of the following conditions:Ground speed of aircraft = 350 km/h: exposure time = 1/100 s.
Ground speed of aircraft = 350 km/h: exposure time = 1/1,000 s.
Ground speed of aircraft = 200 miles/h: exposure time = 1/500 s.
b. Compare the effects on the photograph of all three situations in part (a).
The Correct Answer and Explanation is:
a. Calculations:
To determine how far the camera moves during the exposure time, use the formula: Distance=Speed×Time\text{Distance} = \text{Speed} \times \text{Time}
We must first convert all speeds to meters per second (m/s).
Case 2:
- Ground speed = 350 km/h = 350×10003600=97.22 m/s\frac{350 \times 1000}{3600} = 97.22 \, \text{m/s}
- Exposure time = 1/100 s
Distance=97.22×1100=0.9722 m\text{Distance} = 97.22 \times \frac{1}{100} = 0.9722 \, \text{m}
Case 3:
- Same speed = 97.22 m/s
- Exposure time = 1/1000 s
Distance=97.22×11000=0.0972 m\text{Distance} = 97.22 \times \frac{1}{1000} = 0.0972 \, \text{m}
Case 4:
- Ground speed = 200 miles/h = 200×1609.34/3600=89.41 m/s200 \times 1609.34 / 3600 = 89.41 \, \text{m/s}
- Exposure time = 1/500 s
Distance=89.41×1500=0.1788 m\text{Distance} = 89.41 \times \frac{1}{500} = 0.1788 \, \text{m}
b. Comparison and Explanation
The distance that a camera moves during exposure affects the sharpness of aerial photographs. This movement causes motion blur if the camera is not properly stabilized or if the exposure time is too long for the aircraft’s speed.
In Case 2, the aircraft is moving at 350 km/h with an exposure time of 1/100 s, resulting in a movement of 0.9722 meters during the exposure. This is nearly 1 meter of motion, which would cause significant blurring unless motion compensation (such as a gyro-stabilized camera mount) is used. This level of blur would be unacceptable for detailed photogrammetric or mapping purposes.
In Case 3, the speed remains the same, but the exposure time is reduced to 1/1000 s. The camera moves only 0.0972 meters, or about 9.7 cm. While still some motion, the blur would be far less noticeable, and for many practical applications, this image would be sharp enough, especially with a fast shutter speed compensating for the aircraft’s motion.
In Case 4, the aircraft travels at a slower speed of 200 miles/h (89.41 m/s), and the exposure time is 1/500 s. The camera moves 0.1788 meters, or about 18 cm. Although this is more than in Case 3, it is significantly less than in Case 2, meaning the image would still be clearer than Case 2 but potentially slightly more blurred than Case 3.
In conclusion, shorter exposure times and slower aircraft speeds reduce the amount of motion blur in aerial photographs. Case 3 produces the sharpest image, followed by Case 4, while Case 2 is most likely to suffer from noticeable motion blur.
