Abstract: A method for measuring longitudinal variation in chromatic dispersion in an optical fiber, comprising: (i) launching into a first end and a second end of optical fiber an optical signal at a wavelength ?1 to collect backscatter power P(z) for different positions z within said optical fiber and providing measured OTDR backscatter traces; (ii) deriving from the measured OTDR backscatter traces at the single OTDR wavelength ?1 either (a) the longitudinal MFD(z) data or (b) the relative MFD data; and (iii) calculating estimated longitudinal dispersion D(z) from the longitudinal MFD(z) data or the relative MFD data, without utilizing any other wavelength data.