Task: Question Generation
Input (English): Passage: Penetration testing involves inserting a probe into snow to determine the snow's mechanical properties.  Experienced snow surveyors can use an ordinary ski pole to test snow hardness by pushing it into the snow; the results are recorded based on the change in resistance felt as the pole is inserted.  A more scientific tool, invented in the 1930s but still in widespread use, is a ram penetrometer.  This takes the form of a rod with a cone at the lower end.  The upper end of the rod passes through a weight that is used as a hammer; the weight is lifted and released, and hits an anvil—a ledge around the rod which it cannot pass—which drives the rod into the snow.  To take a measurement, the rod is placed on the snow and the hammer is dropped one or more times; the resulting depth of penetration is recorded.  In soft snow a lighter hammer can be used to obtain more precise results; hammer weights range from 2 kg down to 0.1 kg.  Even with lighter hammers, ram penetrometers have difficulty distinguishing thin layers of snow, which limits their usefulness with regard to avalanche studies, since thin and soft layers are often involved in avalanche formation.Two lightweight tools are in wide use that are more sensitive than ram penetrometers.  A snow micro-penetrometer uses a motor to drive a rod into snow, measuring the force required; it is sensitive to 0.01–0.05 newtons, depending on the snow strength.  A SABRE probe consists of a rod that is inserted manually into snow; accelerometer readings are then used to determine the penetrative force needed at each depth, and stored electronically.For testing dense polar snow, a cone penetrometer test (CPT) is use, based on the equivalent devices used for soil testing.  CPT measurements can be used in hard snow and firn to depths of 5–10 m.
Output (English): What is the acronym for cone penetrometer test?