How does a runway inspection radar work?
Looking at their patent it appears it uses a multi spectrum system (radar &amp; electro optical) to track all object: birds, aircraft, and FOD.

It uses a radar to detect objects


  The potential foreign object source identifier subsystem preferably includes potential foreign object source detectors such as a tower-mounted millimeter wave sensor (MWS) detector


And a specialized light sensor to determine the makeup of the object


  FOD identification functionality may be added to the FOD detectors, such as functionality which identifies the material which constitutes the FOD. Remote spectrometry functionality, such as that used in mineral prospecting satellites, may be employed for this purpose. 


A neat function too is the ability to determine the where the FOD came from and send pictures of the FOD and the offending source to airport officials


  The ascription output may be presented to an airport official in an airport control center on a display console which may show on a first portion  of a screen, an image of the detected FOD and its location, both preferably in a zoomable format, along with a time stamp, and on a second portion of the screen, an image or other representation of a most probable source of the detected FOD, preferably in a zoomable format, along with its time stamp. 


It appears it also fuses sensor data with aviation data to augment it's determination


  flight database data indicating recent aircraft movements and optical identification data indicating vehicle movements is supplied to data fusion functionality which also receives ASMGCS data and weather data and interfaces


If it works as advertised it not only replaces visual inspection but also provides realtime feedback for bird control and communicating with aircraft falling apart.