To aid in the interpretation of seismic data received from a marine subbottom profiler, a number of digital signal processing techniques are applied. A quadrature bandpass filter with a Gaussian response is used to obtain a display representative of the reflected energy in selected windows within the source pulse spectrum. This type of filtering reveals frequency-dependent features of the sediment without introducing artificial layering because of a ripple-free response. Subsequent processing, differentiation or peak detection further enhance the image for the human interpreter.