TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The method (M1) further comprises: determining a phase difference between the detected backscattered optical signals generated in second sections surrounding a first section to determine characteristics of the measurand, where the detected backscattered optical signals comprise coherent Rayleigh noise; detecting coherent Rayleigh noise generated in at least a subsection of the first section; and using the detected coherent Rayleigh noise to assist unwrapping of the phase difference between the detected backscattered optical signals generated in the second sections surrounding the first section. In method (M1): the first sections comprise coiled lengths of optical fiber coupled to a transducer, where the transducer transduces the measurand to a strain on the optical fiber; and the second sections are shielded to reduce sensitivity to the measurand. The method (M2) further comprises: using detected CRN generated within the first section to guide unwrapping of the phase difference in the CRN between the surrounding second sections; launching many optical pulses into the optical fiber sensor, where the optical pulses comprise a first set of optical pulses having a first characteristic and a second set of optical pulses having a second characteristic that is different than the first characteristic; and launching many optical pulses into the optical fiber sensor, where the optical pulses include a first pulse having a first wavelength and a second pulse having a second wavelength, determining a distributed response along the length of the optical fiber sensor from the CRN generated in response to the first pulse, and determining individual responses from the first sections having the enhanced sensitivity from the CRN generated in response to the second pulse. In method (M2): acquiring the distributed measurement comprises detecting coherent Rayleigh noise (CRN) generated by the optical fiber sensor in response to optical pulses launched into the optical fiber sensor, and comparing phases of the CRN generated in second sections surrounding a first section to determine characteristics of the measurand; and each first section includes a length of optical fiber coupled to a transducer configured to respond to the measurand, and each second section includes a length of optical fiber shielded from the measurand. Preferred Components: In method (M1): the first sections comprise at least one of fiber optic hydrophones, fiber optic accelerometers, fiber optic gas composition sensors and photoacoustic spectrometers; and the successive launched optical pulses comprise a first set of optical pulses and a second set of optical pulses, where the first set of optical pulses has at least one of a wavelength, frequency, and/or polarization that is different than the second set of optical pulses. In the system (I), the interrogation and acquisition system: is further configured to use the detected CRN generated within the sections of higher sensitivity to assist unwrapping of the phase difference; comprises an optical source for launching first optical pulses to measure a distributed response along the length of the fiber optic distributed sensor and second optical pulses to measure individual responses from the sections of higher sensitivity; and comprises an optical source for launching many optical pulses into the fiber optic distributed sensor, where the optical pulses comprise a first set of pulses having a first characteristic and a second set of pulses having a second characteristic that is different than the first characteristic. In the system (I): the sections of higher sensitivity to the measurand is alternate with the sections of lower sensitivity to the measurand; the sections of higher sensitivity comprise discrete sensors configured to respond to the measurand, where the discrete sensors comprise coils of optical fiber coupled to transducers, and the sections of lower sensitivity comprise lengths of optical fiber that are not coupled to a transducer; the sections of lower sensitivity are shielded from the measurand; the fiber optic distributed sensor further comprises wavelength selective elements at opposing ends of the sections of higher sensitivity; the first optical pulses have a first wavelength and the second optical pulses have a second wavelength that is different than the first wavelength; and the wavelength selective elements are fiber Bragg gratings. In system (II), the executable code, when executed by the at least one processor, further causes the interrogation and data acquisition system: to detect CRN generated by the optical fiber sensor in response to optical pulses launched into the optical fiber sensor and to determine a phase difference between the CRN generated within second regions surrounding a first region to determine characteristics of the measurand; and to use detected CRN generated with the first region to guide unwrapping of the phase difference. EXAMPLE - No suitable example given.