Sentence:  The antenna patterns and the power gain at the peak of the beam were both measured ( Mayer , McCullough , and Sloanaker , 1958 b ) , so that the absolute power <WSD>sensitivity</WSD> of the antenna beam over the solid angle of the moon was known . 
Meaning of the word marked with <WSD> tags:  the ability to respond to physical stimuli or to register small physical amounts or differences