An instrumented aircraft and a vertically-pointing FM-CW radar were used to investigate waves and turbulence within a very strong low-level temperature inversion. Temperature and wind velocity data from the aircraft were spectrum-analyzed to reveal characteristics of gravity waves with lengths between 44 and 560 m. Data from two days, with slightly different inversion conditions, are presented. Nearly all the waves at these wavelengths are trapped waves, propagating horizontally within the inversion. The wave groups are generally of limited horizontal and vertical extent, often occurring wholly within thin sublayers of the inversion. The longer waves tend to have uniformity of direction, while the shorter waves propagate in all directions. Data from aircraft, radar and wind soundings are internally consistent and show that critical layer absorption of some of the waves is probable within the inversion. Some implications for the observation of gravity waves by aircraft are presented. (Author)