Working with Segment ListsLIGO data is not always available. In addition, there are times when data may be available, but of poor quality. For these reasons, most work with LIGO data begins with a "segment list", specifying the times of data to be analyzed.
Finding Segment Lists with TimelineThe Timeline application can be used to find and download segment lists. For example, a segment list of times where H1 data passed the Burst Group's category 2 data quality checks might look like this:
Burst CAT 2 segment list
Each line of the text file corresponds to 1 segment of data that passed the data quality checks. Shown are the GPS start time of the segment, the GPS end time, and the duration (in seconds) of the segment.
We can download both the data and the segment list for this period of time:
Constructing Segment Lists from Data FilesSegment lists can also be constructed directly from LOSC data files. For details, see documentation of the LOSC Example API or the Introduction to LIGO Data Files tutorial. If your prefer to write your own segment API, you may want to see this Matlab example script or read about the structure of LOSC data files.
Types of segmentsLIGO data files contain a variety of segment types. For LOSC, the segments called DATA indicate when strain data is available. Then the segments CAT1, CAT2, CAT3 indicate problems with the data (CAT1 being worst). There are also segments of times when hardware injections are not occuring. For more information, see here for the S5 and S6 runs and here for the O1 run.