A method and an arrangement are provided for producing a computed distribution of speeds of scatterers in a target volume (1701). An estimate distribution of speeds at which scatterers would move in the target volume is provided (1201). It is converted (1202) to a candidate autocorrelation function that represent autocorrelation data points that a pulse radar would measure from the current estimate distribution. The fit of a candidate ACF to a measured ACF is measured (1203). The estimate distribution is accepted if a measured fit fulfills a predefined acceptance criterion, or modified (1205) in which case processing returns to the conversion of the modified estimate distribution to an ACF. An accepted estimate distribution is output (1206) as a computed distribution of speeds that describes the actual distribution of speeds.