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

SeisBase.Nodal.read_nodal — Function

S = read_nodal(fmt, filestr [, keywords])

Read nodal data from file filestr into new NodalData object S.

Keywords

KW	Type	Default	Used By	Meaning
chans	ChanSpec	Int64[]	all	channel numbers to read in
nn	String	"N0"	all	network name in `:id`
s	TimeSpec		silixa	start time [1]
t	TimeSpec		silixa	end time
v	Integer	0	silixa	verbosity

Special behavior: Real values supplied to s= and t= are treated as seconds from file begin; most SeisBase functions treat Real as seconds relative to current time.

Non-Standard Behavior

Real values supplied to keywords $s=$ and $t=$ are treated as seconds relative to file begin time. Most SeisBase 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.

See also: TimeSpec, parsetimewin, read_data

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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

SeisBase.NodalLoc — Type

NodalLoc

Instrument position along a nodal array

Nodal location. Currently only stores position along optical cable.

x::Float64 (meters)
y::Float64 (meters)
z::Float64 (meters)

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SeisBase.Nodal.NodalData — Type

NodalData

SeisData variant for multichannel nodal array data.

NodalChannel

SeisChannel variant for a channel from a nodal array.

Fields

Field	Description
:n	Number of sensors
:ox	Origin longitude
:oy	Origin latitude
:oz	Origin elevation
:info	Critical array info, shared by all sensors. [1]
:id	Channel id. Uses NET.STA.LOC.CHA format when possible
:name	Freeform channel name
:loc	Location (position) vector; only accepts NodalLoc
:fs	Sampling frequency in Hz
:gain	Scalar gain
:resp	Instrument response
:units	String describing data units. UCUM standards are assumed.
:src	Freeform string describing data source.
:misc	Dictionary for non-critical information.
:notes	Timestamped notes; includes automatically-logged information.
:t	Matrix of time gaps in integer μs, formatted [Sample# Length]
:data	Matrix underlying time-series data
:x	Views into :data corresponding to each channel

Not present in, or retained by, NodalChannel objects.

See also: SeisData, InstrumentPosition, InstrumentResponse

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SeisBase.Nodal.NodalChannel — Type

NodalChannel

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

See NodalData.

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