Calculator, system, method and computer program for obtaining one or more motion parameters of a target

A calculator (20) for obtaining motion parameters (26) of the target (14), wherein the calculator (20) is configured to obtain the one or more motion parameters (26) on the basis of at least two time differences. The first time difference describes a timing of passings of a first pair of transmitter-receiver-lines by the target (14), and the second time difference describes a timing of passings of a second pair of transmitter-receiver-lines by the target (14), wherein the second pair of the transmitter-receiver-lines is different from the first pair of transmitter-receiver-lines.