Source : Webster's Revised Unabridged Dictionary (1913)

Radiomicrometer \Ra`di*o*mi*crom"e*ter\, n. [Radio- +
   micrometer.] (Physics)
   A very sensitive modification or application of the
   thermopile, used for indicating minute changes of radiant
   heat, or temperature.

Source : WordNet®

radiomicrometer
     n : radiometer that is extremely sensitive