Step 2: Frequency partitioning

Each trace is now split into two; unaliased, low-frequency (LF), and aliased high-frequency (HF). As usual, the frequecy cut-off should not be too sharp, and in the time domain the LF filter might be a triangularly-weighted sinc function with the HF filter its identity complement. The choice of cut-off may be made either in terms of the lowest velocity event and the trace spacing, or by looking at f-k power spectra tiled to point up aliased energy. At this point the LF data is available for linear spatial filtering.