18.1.1 Terminology

Topic Version	1	Published	12/09/2016	Topic Change History
For Standard	PRODML v2.0

Because DAS is an emerging technology with new and specialized terminology, definitions are provided in this document.

SEAFOM (an international joint industry forum aimed at promoting the growth of fiber optic monitoring system installations in the upstream oil and gas industry) and the Energistics DAS work group have collaborated to define key terms for DAS. A few key terms are defined here for convenience. For a detailed list of definitions, see 22 Appendix for DAS .

Term	Definition
DAS Job	A set of one or more DAS acquisitions acquired in a defined timeframe using a common optical path and DAS instrument box.
DAS Acquisition	Collection of DAS data acquired during the DAS survey.
DAS Instrument Box	The DAS measurement instrument. Sometimes called the “interrogator unit”.
Optical Path	A series of fibers, connectors, etc. that together form the path for the light pulse emitted from the interrogator unit.
Interrogation Rate (or Pulse Rate)	The rate at which the DAS instrument box interrogates the fiber sensor. For most instruments, this is informally known as the pulse rate.
Output Data Rate	The rate at which the measurement system provides output data for all ‘loci’ (spatial samples) along the fiber. This is typically equal to the interrogation rate/pulse rate or an integer fraction thereof.
Trace(or Scan)	Array of sensor values for all loci interrogated along the fiber for a single “pulse.”
Locus (plural Loci)	A particular location that indicates a spatial sample point along the sensing fiber at which a “time series” of acoustic measurements is made.
Measurement Start Time	The time at the beginning of a data “sample” in a “time series.” This is typically a GPS-locked time measurement.
Sample	A single measurement, i.e., the acoustic signal value at a single locus for a single trace.
Spatial Resolution	The ability of the measurement system to discriminate signals that are spatially separated. It should not be confused with Spatial Sampling Interval.
Spatial Sampling Interval	The separation between two consecutive “spatial sample”’ points on the fiber at which the signal is measured. It should not be confused with “spatial resolution.”
DAS Raw Data	DAS data exchange format that describes unprocessed DAS data provided by the vendor to a customer.
DAS FBE Data	A category of “processed” data. DAS data exchange format for frequency band extracted (FBE) DAS data provided by the vendor to a customer. This DAS data type describes a dataset that contains one or more frequency bands filtered time series of a “raw” DAS dataset. For example, the RMS of a band passed filtered time series or the level of a frequency spectrum.
DAS Spectrum Data	A category of “processed” data. DAS data exchange format for frequency spectrum information extracted from a (sub) set of “raw” DAS data.