Suppose you want to process data from both LIGO sites simultaneously (e.g. to study inter-site correlations), but the software you are using can only handle a single list of input frame files. In this case, you will have to merge the data files from the two sites. You can do this with the FrCopy utility, which is part of the Fr package. Given two input files covering the same time interval, you can merge them as follows:
FrCopy -i H-123456789.F -i L-123456789.F -o M-123456789.FNote that each of the input files is preceded by -i ; this is important, so that FrCopy treats them as independent lists. You can, in fact, use a list in each case, e.g.:
FrCopy -i H-12345678*.F -i L-12345678*.F -o M-123456780-123456789.FIf you want to merge just a subset of channels, there are two methods. You can do the channel selection as the merged frame is written out, using the -t flag:
FrCopy -i H-123456789.F -i L-123456789.F -o M-123456789.F -t H0:PEM-LVEA_SEISX L0:PEM-LVEA_SEISYor you can do the channel selection as the input frames are read in, using the -a flag after each input:
FrCopy -i H-123456789.F -a H0:PEM-LVEA_SEISX -i L-123456789.F -a L0:PEM-LVEA_SEISY -o M-123456789.FThe latter method (using -a) is generally faster, but it only works if the input frames include the table-of-contents structure, and it copies only the ADC data, not other data structures such as FrDetector. (Also, it does not work on "version 5" frames written by LDAS.)