We want to make sure that we have an appropriate focal length for capturing our area of interest. We’ve worked out some calculations of the camera’s image ‘footprint’ at various focal lengths and altitudes. Our likely focal length will be between 30-35mm. The graph above shows the footprint or coverage area at various altitudes with a 34mm focal length. There is a polynomial relationship between altitude and image footprint in meters2.
The equation for this relationship is: Y=0.1954x2 + 1.0421x - 7149.7
Y= footprint in meters2 x= altitude in meters
For example, according to this relationship, at 20,000 meters in altitude, we will have a footprint of 78173692 meters2 (or 30.18 miles squared). This relationship was derived using a formula for angle of view ( theta = 2 arctan (d/2f), where f=focal length and d= size of focal plane) and then the formula for one dimensional swath width ( swath width = 2(H tan (theta/2)).
- ryan callihan - camera team