Photo missions are flown mainly in late fall or early spring. Other times of the year are less suitable because of tree foliage, snow, low sun angle, etc. LiDAR can be flown at anytime of day and year as long as the sky is mostly clear, however, it is preferred to fly late fall and early spring as this is when the most ground points can be obtained due to low foliage.
Mission Planning is based on time of request, ground visibility, and sun angle. The area to be flown is mapped, flight lines established, targets set up if needed, and required flight heights established.
In Ohio there are just a few good flying days during a year. In the summer the ground is obstructed by tree leaves and grass. In the winter the ground may be covered by snow, or the sun angle is low and the ground details are hidden in shadows. Only two periods of the year (early spring and late fall) are suitable for photo missions. However, sometimes the atmospheric conditions (clouds, haze, etc.) limit hte visibility. This leaves only a handful of days suitable for aerial photography.
Aerial targets are used to mark control points on the ground. The targets are usually shaped as a cross; round targets are occasionally used for high accuracy work. Typical target size for large scale mapping is about 5' for cross targets and 3' for round targets.
Targets should be on a flat ground and be visible form the airplance (with no obstructions within 45 degrees from the vertical in any direction).
Sometimes it is necessary to paint the target background black to provide good contrast.