A pipeline inspection and defect 
mapping system includes a pig having an 
inertial measurement unit and a pipeline inspection unit for recording pig location and defect detection events, each 
record time-stamped by a highly precise onboard 
clock. The 
system also includes several magloggers at precisely known locations along the pipeline, each containing a fluxgate 
magnetometer for detecting the passage of the pig along the pipeline and further containing a highly precise 
clock synchronized with the 
clock in the pig. The locations of the various magloggers are known in a north / east / down coordinate 
system through a differential global positioning 
satellite process. Finally, a postprocessing off-line computer 
system receives downloaded maglogger, inertial measurement, and 
odometer data and through the use of several Kalman filters, derives the location of the detected defects in the north / east / down coordinate frame. Consequently, a task of identifying sites for repair activity is much simplified.