The imaging detector parameter, instantaneous field of view (IFOV), is often specified in milliradians (mrad). Given that 2p radians equal 360 deg, a milliradian is a planar angular measure corresponding to approximately 0.0573 deg.
According to NIST, the official definition of a radian is “the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius.” This definition is depicted in Fig. 3.1. Note that while the unit, radian, is strictly defined according to the circle shown, the angle enclosed by the circle’s arc and the angle enclosed within the dashed lines are the same, u.
Imaging detectors in UAVs are formatted in arrays, the smallest element of which is called a pixel. A value for the IFOV enables the calculation of the ground sample distance (GSD) corresponding to one pixel, given information about the sensor’s altitude and range to the target.
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