Analytic
LIght Detection And Ranging uses the same principle as RADAR. The lidar instrument transmits light out to a target. The transmitted light interacts with and is changed by the target. Some of this light is reflected / scattered back to the instrument where it is analyzed. A rangefinder scans beneath the aircraft, producing a wide swath over which the distance to the ground is measured. In post-flight processing, the laser range, scan angle, GPS data and IRS data are combined to determine the position of a point on the Earth's surface accurately.
Distributed Sensing
Distributed sensing is a technique whereby one sensor can collect data that is spatially distributed over many thousands of individual measurement points. In conventional sensing, an individual sensor such as a thermocouple or platinum resistance probe is needed for each point of interest. The advantages of distributed sensing over conventional sensing are clearly apparent in applications where temperature profiles are required over long distances or large areas such as reservoir monitoring, and pipeline structural monitoring and leak detection.
Traditional temperature logging of oil wells is accomplished by surveying with quartz electronic memory gauges (EMG?s) or similar instruments. Using optical fiber is a cost effective way to cover a large area with very small sensor. Many measurement points can be addressed simultaneously along the fiber. The data acquisition is performed by a single processor and be collected in a centralized data handling equipement. The installation and maintenance of optical fiber does not require special equipement and is rather simple.
Working principle: The optical fiber distributed-temperature sensor is based on optical time-domain reflectometry (OTDR), which is commonly referred to as ?backscatter.? In this technique, a pulse of light is launched into the sensing fiber through a directional coupler.
