  We present Inverse Airborne Optical Sectioning (IAOS) an optical analogy to
Inverse Synthetic Aperture Radar (ISAR). Moving targets, such as walking
people, that are heavily occluded by vegetation can be made visible and tracked
with a stationary optical sensor (e.g., a hovering camera drone above forest).
We introduce the principles of IAOS (i.e., inverse synthetic aperture imaging),
explain how the signal of occluders can be further suppressed by filtering the
Radon transform of the image integral, and present how targets motion
parameters can be estimated manually and automatically. Finally, we show that
while tracking occluded targets in conventional aerial images is infeasible, it
becomes efficiently possible in integral images that result from IAOS.
