After a dive at a 45 degree angle into the ground...
you multiply the depth of the hole, in inches times the length of the debris field
ahmm....I used a variation of that technique one time. I was flying a Formula One some years back on a very windy day and started doing a series of long downwind dives. The last dive ended when the plane didn't pull out completely and it skipped into the concrete runway. About 600 feet from the impact was the engine.
By measuring the angle of the groove formed in the spinner where it first touched and knowing the RPM of the engine and diameter of the spinner, I was able to calculate the ground speed when it hit.