1. A measurement instrument for capturing signal data based upon an autocorrelation trigger comprising: a processor that provides a three-dimensional representation of frequency versus time versus amplitude to a monitor; a correlator detector for producing a correlation coefficient by correlating a signal with a time-delayed version of the signal; a lag generator providing the time-delayed version of the signal to the correlator detector; a comparator connected to the correlator detector for producing a trigger when a correlation condition is satisfied; and an acquisition memory to hold information related to the signal in response to the trigger signal; wherein the comparator comprises a correlator for correlating a correlation series, which comprises a series of correlation coefficients, with a correlation map to determine whether the correlation condition is satisfied.