This paper investigates the automated detection of jet contrails using data from the Advanced Very High Resolution Radiometer (AVHRR). A preliminary algorithm subtracts the 11·8  image from the 10·8  image, creating a difference image on which contrails are enhanced. Then a three-stage algorithm searches the difference image for the nearly-straight line segments which characterize contrails. First, the algorithm searches for elevated, linear patterns called ‘ridges’. Second, it applies a Hough Transform to the detected ridges to locate nearly-straight lines. Third, the algorithm determines which of the nearly-straight lines are likely to be contrails. The paper applies this technique to several test scenes.