Signal design in cf-bats is hypothesized to be commensurate with the evaluation of time-variant echo parameters, imposed by changes in the sound channel occurring as the bat flies by a target. Two such parameters, the proportional changes in Doppler frequency and sound pressure amplitude, are surveyed, employing a simplified acoustic model in order to assess their fitness for target localization given a translational movement within a plane. This is accomplished by considering the properties of the scalar fields given by the value of these putative sensory variables as a function of position in a plane. The considered criteria are: existence and extent of ambiguity areas (i.e., multiple solutions for target position), magnitude of the variables (relevant with regard to perceptual thresholds), as well as magnitude and orthogonality of the gradients (relevant to localization accuracy). It is concluded that these properties render the considered variables compatible with gross judgements of target position. This may be sufficient for behavioral contexts like obstacle avoidance, where adoption of suitable safety margins could compensate for the variance and bias associated with estimates of target location.