A system for estimating a wellbore parameter includes a first component located at or near a terranean surface; a second component at least partially disposed within a wellbore at or near a subterranean zone; and a controller communicably coupled to the first and second components. The second component is associated with a sensor. The controller is operable to: adjust a characteristic of an input fluid to the wellbore through a range of input values; receive, from the sensor, a plurality of output values of the input fluid that vary in response to the input values, the output values representative of a downhole condition; and estimate a wellbore parameter distinct from the downhole condition based on the measured output values.