During the NLC-93 rocket campaign at Esrange, Sweden, the vertical structure of a noctilucent cloud layer has been investigated in situ. As in earlier rocket flights, combinations of scattered light detectors and electrostatic impact probes have been applied. While the photometric measurement provides the total downward radiance scattered from the cloud particles, the impact probe yields local information about the particle properties. The responses of both techniques scale differently with the particle size. This feature is utilized to derive information about the height dependence of the particle population. The analysis of three NLC passages indicates little vertical variation of the population throughout most of the layer. The lower part of the cloud is characterized by an increase in particle size and a decrease in particle density towards the cloud base. This is to be expected for an NLC brightness peak caused by large particles sedimenting out of the cloud. Implications for the dynamical structure of the cloud are discussed. ¿ 1998 American Geophysical Union