  We introduce and describe a technique for distance sensing, based on
second-order interferometry of thermal light. The method is based on measuring
correlation between intensity fluctuations on two detectors, and provides
estimates of the distances separating a remote mask from the source and the
detector, even when such information cannot be retrieved by first-order
intensity measurements. We show how the sensitivity to such distances is
intimately connected to the degree of correlation of the measured interference
pattern in different experimental scenarios and independently of the spectral
properties of light. Remarkably, this protocol can be also used to measure the
distance of remote reflective objects in the presence of turbulence. We
demonstrate the emergence of new critical parameters which benchmark the degree
of second-order correlation, describing the counterintuitive emergence of
spatial second-order interference not only in the absence of (first-order)
coherence at both detectors but also when first order interference is observed
at one of the two detectors.
