Sentence:  The ratio of the measured antenna temperature change during a drift scan across the moon to the average brightness temperature of the moon over the antenna beam ( assuming that the brightness temperature of the sky <WSD>is</WSD> negligible ) was found , by graphical integration of the antenna directivity diagram , to be 0.85 . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)