A technique includes using at least one emitter to generate a first optical signal to propagate along a first optical path to interact with a target, to generate a second optical signal and generate a third optical signal to propagate along a second optical path other than the first optical path to generate a fourth optical signal. The technique includes using at least one receiver to acquire a first measurement of the second optical signal and acquire a second measurement of the fourth optical signal. The technique includes generating an indication of a parameter that is associated with a target, which includes scaling a ratio of the first and second measurements based at least in part on optical communication between the emitter(s) and the receiver(s) that does not involve interaction with the target.