Dictionary:Vertical seismic profile (VSP) processing
The first step is usually a slant-path correction to traveltimes because the raypath is not vertical. The sonde depth z divided by the first-break times tv gives the average velocity V(z) and Δz/Δtv gives the interval velocity Vi. The energy that arrives shortly after tv is relatively free of multiples and is used to make a corridor stack (sometimes called an outside corridor stack). If tv(z) is subtracted from each trace, downgoing arrivals are emphasized and if tv(z) is added to each trace, upgoing arrivals are emphasized. If the source generates S-waves and a 3-component geophone is used, the downgoing S-wave can usually be seen and if its traveltimes are added to each trace, S-wave reflections become evident. Other types of processing are also done to VSP data or to data involving appreciable offsets.