Why the camera is a good aerial sensor

We can use a number of different sensors for aerial vehicle use. We can name sonar, radar, lidar, GPS and camera as the most commonly used sensors.
The principle working behind sonar, radar and lidar are all nearly the same in that they all send out a signal that hits a target and returns. By intercepting this returning signal, the device can provide an estimate of the position of the objects in relation to the vehicle. Thus these devices are known as active devices.
The GPS on the other hand is a passive device that relies on the signals sent out by a number of satelites that orbit the earth. By calculating the time difference between the reception of these signals the GPS can calculate its own position in relation to the satelites and also in relation to the earth.
Finally we have the camera that senses the incomming rays of light from a large number of directions and provides an image that represents the strength of these rays.
For use in localization of course the GPS is the best choice, but there are situations in which the use of GPS or related technologies may not be possible. For example indoor environments or in between large buildings can have an unwanted effect on the signals that are sent by the satellites. Further problems are posed in combat situations where the signals may be jammed by the adversaries.
The problem with sonar is that, in high altitudes, a long time is required for the signal to reach earth and also the signal is dispersed alot