With Marty Klein's introduction of dual frequency (nominally 100 kHz and 500 kHz) side scan sonar, it was apparent that spatially and temporally coincident backscatter from any given seabed at those two widely separated acoustic frequencies, would likely provide two separate and unique images of that seascape. Admittedly, the along-track insonification and receiving beam patterns were different, and due to the absence of bathymetric data, the precise backscatter grazing angles were unknown. However, the overlapping sets of side scanning across-track grazing angles at the two frequencies were always the same.