My Tickets

Drivers Manual

GeoSwath Sonar (125 KHz) Port Head - 20

Description

Driver that decodes bathymetry and sidescan data from a GeoAcoustics GeoSwath+ (GS+) Interferometric Sonar System.

This system can be categorized as an enhanced sidescan system that delivers geo-referenced backscatter samples, with multiple transducer groups per head, phase detection and advanced data processing.
An angle can be obtained per sample.

The sonar system broadcasts UDP packets to port 5001 over the network to this driver. 
The packets contain:

  • raw angle
  • amplitude
  • travel time per sample
  • quality flag


Driver Information

Driver GeoSwath Sonar (125/250/500 KHz) Interface Type UDP  Driver Class Type -
UTC Driver (question) - Input / Output Input and Output  Executable DrvGeoSwath.exe 
Related Systems
Related Pages

Decoding Notes

Within QINSy each sample is interpreted as a beam. A single swath contains thousands of samples, hence translated into thousands of beams; all beams are stored in the database.

The sonar sends packets of maximum 1024 bytes, therefore for the transmission of one ping a number (e.g. 10) of packets are required.
The driver automatically concatenates the packets to a complete ping before decoding. The sonar system consists of two transducers, both tilted about 30 degrees from vertical, that transmit alternatively.
Note that the mounting angle is not always 30 degrees. 
The ping number is incremented every ping.

The time tag from the sonar packets is decoded as the ping time.

Sound velocity used by the sonar is always assumed to be 1500 m/s.; make sure to add an Underwater Sensor system with sound velocity observation to the template for the beam angle correction.

All the samples are decoded as beams.

The sample rate is not reported by the sonar so this should be selected by the user through the Drivers.io options. See below for system configuration.

Data packets

This driver only decodes:

  • swath data
  • sidescan data
  • sound velocity data

Any navigation / attitude / heading data should be interfaced directly into QINSy and is not decoded by this driver.

Sidescan

The decoded samples are ordered in the time domain and output as a sidescan system. Samples received from the port transducer will be stored in the port channel and from the starboard transducer in the starboard channel. The sidescan decoding is subject to some limitations due to the nature of how sidescan data is stored: if the GS+ system is pinging with two transducers then after the starboard data is received, data from the previous port is merged with it and output as one sidescan ping with two channels. The ping time is averaged between port and starboard ping time. If only one side is pinging then a sidescan update is generated with only one channel in it.

Interfacing Notes

For correct interfacing into QINSy it is of vital importance that the computer on which the GeoSwath sonar control program is executed is time synchronized. The GeoSwath computer can be synchronised to UTC by using an NMEA ZDA and a Time Synchronization (formerly PPS) pulse. Refer to manufacturer's documentation for more info. For correct decoding of the ping time it is important that both computers (QINSy PC and GeoSwath PC) use identical Windows time zone settings.

System Configuration

The GeoSwath+ software filters should be set up in such a way that all the samples are broadcast to QINSy with as many online and processing flags as possible.
These flags can be used by QINSy to decimate the data. In order to do this set up the various filters on the GS+ properly (refer to GS+ documentation) so that outliers are filtered and flagged properly.
The flags will be used later on in QINSy to further despike the samples.

Database Setup

Frequency models

The Geoswath comes in three different frequency models :

  • 125 kHz
  • 250 kHz(default)
  • 500 kHz

Make sure to select the same frequency entry for all systems (Sound velocity, Multibeam both heads and Sidescan).
When the wrong frequency is chosen the reported ranges will not be correct, typically 2 times greater/smaller than expected as the operating frequency is also the sample rate.


  • Sound Velocity

    First add an Underwater sensor "GeoSwath Sonar (xxx KHz) (Sound Velocity)" in order to decode the sound velocity with xxx the frequency of your Geoswath system; select port number 5001.

     
     
  • Multibeam

    Add two multibeam systems, one for the port transducer and one for starboard transducer.
    For the port head select driver "GeoSwath Sonar (xxx KHz) Port Head".
    For the starboard head the driver "GeoSwath Sonar (xxx KHz) Starboard Head".

    IP port number is 5001 for both heads. 

    To control the GS+ from QINSy enable the option 'Control System from QINSy'.
    Online control options for the GS+ can be found in the Echosounder Settings in the Controller.

    The maximum number of beams depends on the operating range of the sonar, typically leave this at 9999.
    Enter about plus 60 degrees roll offset for the port head and minus 60 for the starboard head.

    The Node should be defined per transducer.
    The center of the face of the transducer can be considered as the acoustic center and should be entered as the node offset.

    On the last page of the multibeam system wizard it is possible to enable the Sound Velocity Beam angle correction.
    Select the sound velocity observation here that you defined earlier. 
    Do not do this if the correction is done by the Geoswath (option called Broadcast TXDCR Corrections enabled).


  • Side Scan

    Add a Sidescan System "GeoSwath Sonar (xxx KHz)", Select "Associated Multibeam System" to the port head multibeam system.
    Add two channels, first port, second starboard.
    Select appropriate node for the channels.
    All other fields are not applicable.


After you go online check that only one Geoswath.exe is found in the Task Manager.
If you find more than one please go back to Database Setup and make sure that for every system the correct driver is chosen with the same frequency (and hence command line parameter).

Online

Data Reduction

Two options for data reduction can be used: in the GeoSwath software or in QINSy.

GeoSwath beam reduction

The sonar data from the GeoSwath is flagged after the filters/reduction are applied. To use only the data flagged as good, block on Quality outside Min/Max to 0. The GS+ data reduction does not need to be enabled.

QINSy reduction 

  1. Maximum beam count

    A smart beam reduction algorithm is introduced to cope with the great number of samples that are reported by this sonar system. Since every sample is translated in the driver to a beam, the CPU load caused by processing beam data from a system that pings with 15 Hz/3000 beams per swath can be too much for the pc in order to process footprints in real time. Activate the reduction. Go to "Echosounder settings" dialog, for interferometric systems the line  "Max. beam count" is added to the reduction options. This works independently of the other reduction methods. Typically enable this option and select 300 here. Depending on range/sound velocity profile point count and resulting CPU load the number of kept beams may be increased/decreased.

  2. Median binning reduction
    Input is just one figure: the bin size.
    The calculated footprints are grouped in bins based on the horizontal distance between the transducer and the footprints.
    The bin size is defined by the user. For every group of footprints that fall inside the bin only the median (based on Z) footprint is accepted, the others will be flagged "reduced". 
    By utilizing this reduction method, outliers will typically be removed, which can be useful for reducing Interferometric sonar data, characteristically these systems produce a large band of noise.

    Example: User sets up a bin size of 1 meter. Bins that are located at a distance between 0 and 1 meter at starboard side fall inside bin1, between 1 and 2 meters at bin2 etc. On the port side the same but then bin-1, bin-2 etc. 
    If within a bin multiple footprints are stored then the footprint with median Z value is selected, for example, 3 footprints: -10.2, -10,4, -10.0, the median value is -10.4 so this is the accepted beam, the others are reduced.
    If the swath covers a horizontal range of 50 meters then remember that with binsize of 1 meter the reduced beam count will be only 50.

    Typical bin size values are 0.1 to 0.5 meters.


Figure: Max. Beam Count set to 300 beams, Quality blocking enabled

Tip

For more details on these QINSy data reductions press F1 in the Echosounder Settings online.

Tip

To reduce the CPU load it is advised to use the data reduction in the GeoSwath.

Sound Velocity

The GeoSwath software calculates the beam angles from phase with a fixed Sound Velocity of 1500 m/s so therefore the beam angle corrections need always be applied. This can be done by the Geoswath or by QINSy.  

  • When this is done by QINSy this implicates that the Mini SvS Sound Velocity Probe data should always be interfaced into QINSy for the beam angle correction.
  • When done by the Geoswath (option called Broadcast TXDCR Corrections) then do not use the option in QINSy.

This driver can also be used to control the system settings of the GeoSwath+ system in multibeam mode. This needs to be enabled in the Database Setup.
If enabled the options are accessible in de Controller - Echosounder Settings dialog to order the GS+ system to start or stop pinging, change the range etc.


Figure: Remote Controlling the GS+ Echosounder from QINSy


System Control

The operating settings of the sonar are modified through the Echosounder Settings dialog Control tab of the Controller.

The following settings can be modified:

Setting Description
Pinging Enables and disables pinging.
Tx Mode

Select from Off, Port, Starboard, Both.

When selected this turns on the transmit pulse to the transducers. 

Note: For the Geoswath 4, this option has no effect as the system will keep transmitting on both heads.

Test Pattern

Switches the Test Pattern on and off.

This command will set or reset the diagnostics test signal. When set on, the system will show a test pattern in the ping data indicating that the sonar system transceiver section is working.
The same signal is applied to all four receivers.
If there are no problems with the GeoSwath Plus circuit boards then all data points will have a return angle perpendicular to the transducer face, an inverted V will be seen in the depth display.

Note that the test signal does not give any indication of possible faults with either the transmitter board or the transducers/cables.
If the vessel is moving then you will see the cross profile and depth waterfall displays moving with the vessel motion.

Group Filter

Enables and disables the Group Filter.

When enabled the group filter is applied to the data prior to logging. Filtered-out points are not logged but discarded.

The filter works through the range/angle samples in each ping in forward order. Samples are rejected if the sine of the angle is greater than a (learning) threshold.
Points that are not in groups tend to be removed: this can be thought of as a spike filter operating on sine values.

Bottom Tracking Filter

Enables and disables the Bottom Tracking Filter.

When enabled the bottom tracking filter is applied to the data prior to logging. Filtered-out points are not logged but discarded.

The filter works through the range/angle samples in reverse order generating a continuous mean of the sines and rejecting sines outside a threshold (approx ±17°).
The result is that points are removed if sine values are wildly away from the general trend of the data. This can be thought of as a very loose bottom tracking filter starting at far range.

Water Column Filter

Select from Off, Manual or Automatic.

Setting for water column filter, in meters below transducers.

When enabled for Manual or Automatic mode the filtered points are flagged during acquisition (as ACQ_WATERCOLUMN in the rdf-file/stream) so that the filter may be undone when post-processing.
When Automatic is enabled the height of the water column filter is automatically set based on the mean water depth. Note this should not be used in areas of rapidly changing seabed topography or in very shallow water.
If the Automatic setting is off then the water column filter can be set in the text field below.

When this filter is applied during post-processing the filtered points are flagged as SWATH_LIMITS in the processed swf-file.

Water Col. Filter Height

Enter Min = 1, Max = 9999

When Water Column Filter is set to Manual, enter the height of the water column in meters below the transducers.

Range

Enter Min = 5, Max = 395

Up to 12x depth relative to the transducer positions and the vessel upon which the transducers are fixed.

The range is effectively HALF the listening time after each transmit pulse.
The ping rate is the number of pings per second (pps) and will depend on the range set.

Pulse Length

Enter Min = 1, Max = 7

This sets the length of the transmit pulse in the water, (typically set at 1) which gives a pulse length of 16 cycles. Longer ping lengths give poorer resolution.

For 125kHz system, transmit pulse length is 128µs to 896µs, i.e. 7 steps of 128µs step size.
For 250kHz system, transmit pulse length is 64µs to 448µs, i.e. 7 steps of 64µs step size.
For 500kHz system, transmit pulse length is 32µs to 224µs, i.e. 7 steps of 32µs step size.

Power

Enter Min = 1, Max = 10

Typically set at level 1.
In standard mid water depth survey conditions power levels of 10 can be used to increase the signal levels.
In shallow waters a signal level of 5 or less may be necessary to prevent the side-scan signal from saturating (being limited by the input protection diodes on the receive staves).
This will be seen in the side-scan image as a dark band in the center of each line -  typically in 15m and less water depth the power setting might need to be reduced, especially if the survey is over a hard seafloor.
Note that the Power should not be adjusted during a survey, as this will cause banding in the side-scan mosaic and GeoTexture processing will not be usable.

Sidescan Gain

Enter Min = 1, Max = 4

This sets the gain for the Side Scan channel, (typically set at 1 or 2 for normal use). In deeper water (e.g. >50m deep) and softer bottoms this may need to be increased.

Info

Kongsberg recommend increasing Sidescan Gain first; it doesn't improve SNR but maximizes dynamic range of the side scan signal.
Then increase Power which effectively increases SNR, although in shallow water this should be kept as low as possible.
They depend very much on the frequency of the system, the average depth, the type of water (absorption) and the type of sea bottom.

Info

Units: In the GS software the current units are displayed adjacent to the Ping Length value.
The default is meters. Clicking on the units button will globally toggle the units of GS+ to US Survey feet .

Drivers IO Notes

125:

Use for 125Khz sonar systems

500:

Use for 500Khz sonar systems