Abstract
The generalized radiance can never be measured at a given point of phase space, on account of the finite resolution of any real instrument; instead the instrument averages the radiance over some region of phase space. Thus a negative radiance is never measured, in spite of the fact that the generalized radiance can take on negative values. The relationship between the generalized radiance and the measurement process can be quantified by the instrument function, which is a property of the measurement apparatus and which allows one to calculate the response of the apparatus to any given incident wave field. The instrument function reveals a kind of reciprocity between the wave field being measured and the measurement apparatus. The theory of the instrument function is developed, and examples are discussed.
© 1995 Optical Society of America
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