Precision Acoustics Systems data files

The Precision Acoustics HARP format can contain two types of raw variable:

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.

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