Recovering a short timescale signal from a pair of long-delay visars

We introduce the benefits of analyzing VISAR data in the Fourier domain, particularly for recovering the short time scale signal component. In particular, by combining data from two VISARS having different long delays, we effectively reproduce the short time resolution ability of a short delay while retaining the superior sensitivity to absolute velocity of a long delay. Two different delays are generally desired, not only to untangle integer fringe skips, but to circumvent the fact that a single VISAR cannot record signal components of frequencies periodic with its reciprocal delay. Combining two different delays solves this. We treat the VISARs as linear filters and process and combine the signals in the Fourier domain with a direct equation, without any iteration of time-retarded equations. The technique is demonstrated with a numerical simulation.