Normally, when an autoregression filter (PEF) predicts a value at a point it uses values at earlier points. In practice, a gap may also be set between the predicted value and the earlier values. What is not normally done is to supplement the fitting signals on nearby traces. That is what we do here. We allow the prediction of a signal to include nearby signals at earlier times. The times accepted in the goal are inside a triangle of velocity less than about the water velocity. The new information allowed in the prediction is extremely valuable for water-velocity events. Wavefronts are especially predictable when we can view them along the wavefront (compared to perpendicular or at some other angle from the wavefront). It is even better on land, where noises move more slowly at irregular velocities, and are more likely to be aliased.
Using lopef , the overall process proceeds independently in each of many overlapping windows. The most important practical aspect is the filter masks, described next.