Post-processing method to extend the functional range of optical backscatter reflectometry in extreme environments

Abstract

A system and method for determining an object characteristic from a timed sequence of measured characteristics wherein the object characteristic is determined based on a comparison of a current measured characteristic against a variable reference characteristic. The variable reference characteristic is selected by iterating through the timed sequenced and determining a separate quality metric for the current measured characteristic against each earlier measured characteristic and selecting the variable reference as a function of the determined quality metrics. In one embodiment, iteration continues only until an earlier measured characteristics is found with a quality metric that meets or exceeds a threshold value. In another embodiment, iteration continues through a plurality of earlier measured characteristic (perhaps all) and the variable reference is selected as the earlier measured characteristic with the highest quality metric. The measured characteristics may include OFDR measurements.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A system comprising:
 a data processing apparatus communicatively coupled with a sensor configured to measure a first characteristic of a physical medium; and   memory communicatively coupled with the data processing apparatus, the memory encoding instructions that, when executed by the data processing apparatus, cause the system to perform operations comprising:   receiving, from the sensor, a timed sequence of measurements of the first characteristic of the physical medium; and   determining a set of values of a second characteristic of the physical medium corresponding to the timed sequence of the first characteristic's measurements, wherein the set of second characteristic's values is determined by performing, for each measurement of the timed sequence, operations comprising:
 determining a quality value for the measurement based on a reference measurement selected from among earlier measurements of the timed sequence, wherein the reference measurement is selected by iterating through the earlier measurements and selecting the reference measurement based on the quality value, 
 determining a change of the measurement relative to the reference measurement, and 
 determining a value of the second characteristic of the physical medium based on the measurement's change. 
   
     
     
         2 . The system of  claim 1 , wherein determining the quality value for the measurement based on the reference measurement comprises calculating a correlation between the measurement and the reference measurement. 
     
     
         3 . The system of  claim 1 , wherein the reference measurement is selected by starting with the first measurement and iterating through the earlier measurements, until the quality value meets or exceeds a target-quality value. 
     
     
         4 . The system of  claim 1 , wherein the reference measurement is selected by iterating through a plurality of the earlier measurements and selecting the earlier measurement with a highest quality value from among the plurality of the earlier measurements. 
     
     
         5 . The system of  claim 1 , wherein determining the change of the measurement relative to the reference measurement comprises calculating a shift of the measurement relative to the reference measurement. 
     
     
         6 . The system of  claim 1 , wherein
 the sensor comprises an optical fiber,   the physical medium comprises a portion of the optical fiber extending along the longitudinal axis of the optical fiber,   a measurement of the first characteristic of the optical fiber comprises a scan of OFDR measurements performed over a spatial extension corresponding to the portion of the optical fiber, and   the second characteristic of the optical fiber comprises one of temperature of the portion of the optical fiber or strain in the portion of the optical fiber.   
     
     
         7 . The system of  claim 6 , wherein determining the change of the measurement relative to the reference measurement comprises calculating a spectral shift. 
     
     
         8 . The system of  claim 6 , wherein the optical fiber is disposed in a harsh environment that comprises one or more of high temperature, neutron irradiation, or aerospace. 
     
     
         9 . The system of  claim 6 , wherein the data processing apparatus is implemented as one of a microprocessor, an FPGA, or an ASIC. 
     
     
         10 . A method for post-processing a timed sequence of measured characteristics of a physical medium to obtain an object characteristic, comprising the steps of:
 for a current measured characteristic:
 individually comparing the current measured characteristic with one or more prior measured characteristics in the timed sequence of measured characteristics to determine a separate quality metric associated with the current measured characteristic and each of the one or more prior measured characteristics; 
 as a function of the quality metric, selecting one of the one or more prior measured characteristics to function as a variable reference for the current measured characteristic; 
 determining a change of the current measured characteristic relative to the selected variable reference; and 
 determining the object characteristic of the physical medium based on the change of the measurement characteristic relative to the variable reference. 
   
     
     
         11 . The method of  claim 10  wherein the quality metric is a measure of a correlation between the measured characteristic and the prior measured characteristic. 
     
     
         12 . The method of  claim 11  wherein the quality metric is further defined as a geometric mean quality. 
     
     
         13 . The method of  claim 10  wherein the step of comparing the measured characteristic with one or more prior measured characteristics further includes:
 sequentially comparing the current measured characteristic with one or more prior measured characteristics until a prior measured characteristic is found with a quality value that meets or exceeds a target-quality value; and 
 wherein the step of selecting the variable reference includes selecting as the prior measured characteristic with a quality value that meets or exceeds a target-quality value as the variable reference. 
 
     
     
         14 . The method of  claim 12  wherein the step of comparing the measured characteristic with one or more prior measured characteristics further includes:
 sequentially comparing the current measured characteristic with a plurality of prior measured characteristics to determine a separate quality value for each current measured characteristic and prior measured characteristic pair; and 
 wherein the step of selecting the variable reference includes selecting the prior measured characteristic with the greatest quality value as the variable reference. 
 
     
     
         15 . The method of  claim 10  wherein the physical media is an optical fiber and the timed sequence of measured characteristics includes a timed sequence of OFDR measurement obtained from the optical fiber. 
     
     
         16 . The method of  claim 10  wherein the physical media is a portion of an optical fiber extending along the longitudinal axis of the optical fiber; and
 wherein the timed sequenced of measured characteristics includes a timed sequence of OFDR measurements performed over a spatial extension corresponding to the portion of the optical fiber. 
 
     
     
         17 . A system for determining an object characteristic of a physical media from a timed sequence of measured characteristics of the physical medium, comprising:
 a memory storing a timed sequence of measured characteristics obtained from a sensor; and   a processor coupled to memory, the processor configured to determine the object characteristic associated with a target measured characteristic based on a comparison of the target measured characteristic with a reference measured characteristic selected from among the timed sequence of measured characteristics;   wherein the reference measured characteristic is selected by the processor from among the timed sequence of measured characteristics based on a quality metric, the quality metric representing a level of correlation between the target measured characteristic and the reference measured characteristic; and   wherein, upon selection of the reference measured characteristic, the processor determines the object characteristic associated with the target measured characteristic as a function of a change between the target measured characteristic and the selected reference measured characteristic.   
     
     
         18 . The system of  claim 17  wherein the processor selects the reference measured characteristic by iterating through the timed sequence of measured characteristics, for each iteration calculating the quality metric between the target measured characteristic and one of the measured characteristics in the timed sequence of measured characteristics, and selecting as the reference measured characteristic, the first of the measured characteristics found to have quality metric that meets or exceeds a threshold value. 
     
     
         19 . The system of  claim 18  wherein the timed sequence of measured characteristics includes a sequence of OBR measurements obtained from a fiber optic over time; and
 wherein the object characteristic is one of temperature or strain. 
 
     
     
         20 . The system of  claim 17  wherein the processor selects the reference measured characteristic by iterating through a plurality of the timed sequence of measured characteristics, for each iteration calculating the quality metric between the target measured characteristic and one of the measured characteristics in the timed sequence of measured characteristics, and selecting as the reference measured characteristic, the measured characteristics found to have the highest quality metric.