Last Update: November 16, 2004
Important Points and Assumptions
1- NOAA T-Phase data contains signals
for the low frequency range, e.g. 100 or 250 Hz; therefore, it is likely no audio
can be produced from the T-Phase data stored into a WAV file.
2-The retrieved
WAV file can be very large. Software
that reads a WAV file might reach the limits of the software
memory with these particular files.
3-The sample
rate stored in the FMT Chunk is "round", i.e. it
is not the true rate. The true sample rate is stored
in the additional header.
4-In the header, the
NOAA chunk is added. It
contains the same header information which includes the start/end
times and more as described in the NOAA
internal format.
5-A WAV
file is a binary file; data values are stored in Little Endian
format.
The WAV file output option has been made available
as there are many commercial software packages that read WAV file
data. It is assumed that users who
choose the WAV format as the output option know how to work with
the WAV files. Therefore,
only essential format information is provided here.
WAV Data File Structure
In general, a wav file has at least 3 sections
as shown below:
|RIFF Chunk|FMT Chunk|DATA Chunk|
The detailed descriptions of these chunks can be
found in many web sites.
For example:
http://www.coe.uncc.edu/~danderse/www/wav-format.html
http://ccrma-www.stanford.edu/courses/422/projects/WaveFormat/
or use any Search Engine and look for "RIFF' and/or "WAV".
NHP's WAV Data File Structure
NHP wav files have the same structure as a general
WAV file except an additional NOAA Chunk is added:
|RIFF Chunk|FMT Chunk|NOAA Chunk|Data Chunk|
The NOAA Chunk is a header of the NHP
(NOAA HydroPhone) data file.
NHP Header Contents
When the NOAA header chunk in bytes are obtained,
the contents of the header can be shown by converting the header bytes
into characters. The following is an example of the header which can
also be found in the NOAA internal data format files as well:
Start Time: 1999 360-00:00: 0.000
End Time: 1999 360-23:59:59.991
Sample Rate (Hz): 110.7761690
Sample Size : 2 Bytes (Little Endian)
HPhone Lat (Deg): 31.865383
HPhone LNG (Deg): -34.438017
HPhone Depth (m): 927
Data Source: Model 2v0
N Channels: 1
X, Y, Z (meters): 0, 0, 0
A/D Voltage Range (from 0 to): 5
Mean Voltage approximately: 2.5
Number of Bits of the Digitizer: 8
Hydrophone Sensitivity (dB): -192
Filter Cutoff (Hz): 45
Points from the Pre-Amp Response (for reading the next 2 lines): 8
Hz: 1 2 5 10 20 30 40 50
dB: 35.0 49.0 57.0 60.0 62.0 63.0 64.0 60.0
For the descriptions of the header contents,
please see the NOAA
Internal Data page
For the descriptions of Hydrophone Data in
other formats, see: NOAA
Internal | CSS.
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data
. |
