Header Conventions

The header keys in SEPlib90 are the key to our solution to deal with irregular data. In many cases we will superimpose a grid to ease navigation through a data set (for example we might grid the offset access) , but the main routine will use the higher order of accuracy provided by the header values. SEPlib90 is designed to be as flexible as possible, the user is allowed to create as many header keys, of various types, in any order he wishes. This flexibility is one of the most attractive elements of SEPlib90, but complete anarchy is also unwanted. Without some standards a core set of programs will require an enormous set of user supplied parameters. For example, a NMO routine would require you to supply

• common midpoint key(s),
• offset key(s),
• data record number key,
• common midpoint axis/axes, and
• offset axis/axes.

Such a situation would detract too much from the ease of use that SEPlib is known for. As a result we have reserved certain key names that our core set of programs recognize. To allow ease in transferring from different data types we have based a number of our naming on Colorado School of Mines' Seismic Unix (SU) standards which in turn is based on Barry et al. (1975).

Name Type Description

sx integer Source x location

gx integer Receiver group x location

sy integer Source y location

gy integer Receiver group y location

trid integer Trace status (1= exists 0=padded)

offset integer offset

cdp integer cdp ensemble number

cdpt integer trace number within ensemble

In addition, we have included several other header key conventions that make traversing the data easier, and/or find common use in 3-D processing:

Name Type Description

data_record_number integer Location of trace of given header record

s_x float Source x location

g_x float Receiver group x location

s_y float Source y location

g_y float Receiver group y location

cmp_x float Common mid-point x location

cmp_y float Common mid-point y location

azimuth float Source-receiver azimuth

offset_x float Offset in x location

offset_y float Offset in y location