Precision Acoustics Systems data files
The Precision Acoustics HARP format can contain two types of raw variable:
- single target detections single beam pings - one variable per channel/mode (to a maximum of to 10)
- single target detections split beam pings - one variable per channel/mode (to a maximum of to 4)
Precision Acoustics echosounders produce files with the following naming convention:-
Adddss.ts4
where:
A is a single user-defined letter
ddd is a 3 digit day of the year
ss is a sequence code ranging from 01 to ZZ
There is no way to distinguish split/single beam files from their filename however Echoview will prevent mixing of split/ single beam files within the same fileset.
If more than one file is added to a fileset in Echoview, they must be named in such as way as an alphabetical sorting of the file names will sort them into chronological order. For this reason if a set of files spans more than one year you may need to rename them to use them in a single fileset.
Some Precision Acoustics Systems files can be verified by Echocheck.
Angular position
For split-beam echosounders, the angular position of targets is calculated as follows:
Major-axis angle = (X-axis phase angle - ADC X-axis correction) / PDC X-axis correction
Minor-axis angle = (Y-axis phase angle - ADC Y-axis correction) / PDC Y-axis correction
where:
X-axis phase angle is read from the data file
Y-axis phase angle is read from the data file
ADC X-axis correction is the value defined on the Calibration page of the Variable properties dialog box
ADC Y-axis correction is the value defined on the Calibration page of the Variable properties dialog box
PDC X-axis correction is the value defined on the Calibration page of the Variable properties dialog box
PDC Y-axis correction is the value defined on the Calibration page of the Variable properties dialog box
Single-beam echosounders provide no angular position data.
Target strength
The target strength of targets is calculates as follows:
Uncompensated TS = Raw amplitude - Channel gain - Source level - Static gain
Compensated TS = Uncompensated TS - Beam Compensation
where:
Raw amplitude is read from the data file
Channel gain is the value defined on the Calibration page of the Variable properties dialog box
Source level is the value defined on the Calibration page of the Variable properties dialog box
Static gain is the value defined on the Calibration page of the Variable properties dialog box
and Beam compensation is 0 where no angle data are available (single beam variables) or calculated from angle data as follows:
|
Beam compensation = |
X-axis phase angle - X-axis phase angle correction |
+ |
Y-axis phase angle - Y-axis phase angle correction |
|
X-axis PDI correction |
Y-axis PDI correction |
where:
X-axis phase angle is read from the data file
Y-axis phase angle is read from the data file
X-axis phase angle correction is the value defined on the Calibration page of the Variable properties dialog box
Y-axis phase angle correction is the value defined on the Calibration page of the Variable properties dialog box
X-axis PDI correction is the value defined on the Calibration page of the Variable properties dialog box
Y-axis PDI correction is the value defined on the Calibration page of the Variable properties dialog box
Pulse length
The normalized pulse length is calculated as:
pulse length @ 6dB (normalized) = received pulse length / pulse duration
where:
received pulse length is read from the data file for each single target
PulseDuration (ms) is read from the data file once for all targets in that file
Note for split-beam files
If the Echogram and Properties buttons on the Fileset window are disabled after adding split-beam data files it may be because the data files are missing a required time stamp record.
In split-beam files time records are written asynchronously every 500ms to file, so with short files (less than 500ms) it is likely that this record will be missing. In such situations Echoview displays a warning message box explaining the situation, and marks the file as in error. All such files within a fileset must be removed otherwise the Echogram and Properties buttons will be disabled on the Filesets window.
This does not occur with single beam files because data records contain a full date/time stamp.
See also
Raw Variables derived from Precision Acoustics Systems data files
Calibration settings for PAS data