Patent ID: 7548319
Filing Date: 2009-06-16
Classification: E21B,G01D,G01K,G01L

Abstract:
1. A method of measuring at least one selected parameter at a location within a region of interest, which method comprises the steps of: launching optical pulses at a plurality of preselected interrogation wavelengths into an optical fiber deployed along the region of interest, reflectors being arrayed along the optical fiber to form an array of sensor elements, an optical path length between the said reflectors being dependent upon the selected parameter; detecting the returned optical interference signal for each of the preselected wavelengths; and determining from the optical interference signal an absolute optical path length between two reflectors at the said location, and from the absolute optical path length so determined, the value of the selected parameter at the said location, wherein the step of determining the absolute optical path length comprises carrying out a process in which the derivative of the phase as a function of wavelength is estimated from a subset of the interference signals, using the derivative and an estimated value for the optical path length to estimate the phase relationship between the interference signals, and the phase relationship thus obtained is used to revise the estimated value for the optical path length, the process being repeated for increasing subsets of the remaining wavelengths in sequence, on the basis of the optical path length estimated for the immediately preceding subset in the sequence, thereby to progressively revise the optical path length until it is known to a desired level of accuracy.