(a) appear stationary on the horizon
Collision trajectory implies nil relative motion. However, appearing on the horizon is a sufficient but not a necessary prerequisite for collision. So, no.
(b) appear stationary and increase linearly
Collision trajectory implies nil relative motion. However, as the range decreases, the visual angle of the target must increase with the increase becoming very non-linear at relative close ranges. So, no.
(c) increase linearly
As the range decreases, the visual angle of the target must increase with the increase becoming very non-linear at relative close ranges. So, no.
(d) increase exponentially.
Very much so as the aircraft range gets within the final few seconds prior to impact.
For instance, see fig 5.10 p 142. The graphic plots various speeds against visual angle change but, in effect, is talking about distance against visual angle.
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