A system for covert sensing. A broadband light source is split into two portions, a first portion of which illuminates a target, and a second portion of which is frequency shifted, e.g., by an acousto-optic frequency shifter. Light reflected from the target is combined with the frequency shifted light, detected, and demodulated with an in-phase and quadrature demodulator. The outputs of the demodulator are filtered and the arc tangent of the ratio is calculated.