[en] A straightforward approach to calculating number densities of barium ions at the satellite position following CRRES low altitude chemical releases is described. The calculation is based on a phenomenological model of the neutral barium cloud which is taken to expand collisionlessly as a guassian shell. Ion densities are derived by integrating the photoionization rate along a line extending from the spacecraft position forward into the velocity vector and going through the neutral cloud. Model predictions are compared with in-situ mass spectrometer data, and shown to be in reasonable agreement. 16 refs., 3 figs