Nodal

The Nodal submodule is intended to handle data from nodal arrays. Nodal arrays differ from standard seismic data in that the start and end times of data segments are usually synchronized.

Reading Nodal Data Files

S = read_nodal(fmt, fname [, KWs])

Read data in file format fmt from file fname into memory. Returns a NodalData object.

Supported Keywords

KW	Type	Default	Meaning
chans	ChanSpec	Int64[]	channels to read
nn	String	N0	network subfield in :id
s	TimeSpec	0001-01-01T00:00:00	start time
t	TimeSpec	9999-12-31T12:59:59	end time
v	Integer	0	verbosity

Non-Standard Behavior

Real values supplied to keywords s= and t= are treated as seconds relative to file begin time. Most SeisIO functions that accept TimeSpec arguments treat Real values as seconds relative to now().

Supported File Formats

File Format	String	Notes
Silixa TDMS	silixa	Limited support; see below
SEG Y	segy	Field values are different from read_data output

Silixa TDMS Support Status

• Currently only reads file header and samples from first block
• Not yet supported (test files needed):
  • first block additional samples
  • second block
  • second block additional samples
• Awaiting manufacturer clarification:
  • parameters in :info
  • position along cable; currently loc.(x,y,z) = 0.0 for all channels
  • frequency response; currently :resp is an all-pass placeholder

Nodal SEG Y Support Status

See SEG Y Support.

Working with NodalData objects

NodalData objects have one major structural difference from SeisData objects: the usual data field :x is a set of views to an Array{Float32, 2} (equivalent to a Matrix{Float32}) stored in field :data. This allows the user to apply two-dimensional data processing operations directly to the data matrix.

NodalData Assumptions

• S.t[i] is the same for all i.
• S.fs[i] is constant for all i.
• length(S.x[i]) is constant for all i.

Other Differences from SeisData objects

• Operations like push! and append! must regenerate :data using hcat(), and therefore consume a lot of memory.
• Attempting to push! or append! channels of unequal length throws an error.
• Attempting to push! or append! same-length channels with different :t or :fs won’t synchronize them! You will instead have columns in :data that aren’t time-aligned.
• Irregularly-sampled data (:fs = 0.0) are not supported.

Types

See docstrings for field names and descriptions.

NodalLoc()

Nodal location. Currently only stores position along optical cable.

NodalData()

Structure to hold nodal array data. Similar to a SeisData object.

NodalChannel()

A single channel of data from a nodal array. Similar to a SeisChannel object.