FAQ

 

 

Acoustic Products

 

Why is a GAPS calibration free?

It is mandatory for USBL systems to be calibrated with an INS/AHRS on board of a vessel to give accurate position and attitude to the USBL system. Calibration is not necessary with GAPS because it contains an INS inside of the USBL head. The calibration is done during the manufacture process. In this case, no calibration is necessary by the end user and GAPS can be installed and be operational in less than an hour.

If GAPS is calibration free, why do I need to execute an alignment procedure?

GAPS mixes USBL, INS and GPS technologies to give the most accurate USBL data in its category, it operates in deep or very shallow water and difficult environments where other systems are deficient. As GAPS has an integrated INS, this allows its use without a calibration. Where it is necessary to carefully calibrate all other USBL systems with the INS on board, It is not necessary to carry out this calibration for GAPS, as it is pre-calibrated at our factory with PHINS inside. This will save a lot of time for users and GAPS can be operational in less than an hour. The important point to know is that it is necessary to align GAPS to obtain the best accuracy. This means that it is necessary that the vessel stay with a constant heading during 5 minutes for the coarse alignment, then it is necessary that it move in different directions for 25 minutes for the fine alignment. In only 30 minutes, GAPS will be ready to deliver you the specified accuracy.

What is the maximum submerged depth of GAPS?

GAPS Carbon and GAPS Titanium are officially rated to 25m and 100m water depths respectively.

How can I retrieve the IP address of my GAPS?

By default the IP address is indicated on the GAPS BOX sticker and is 192.168.36.1XX, with XX being the last two numbers of the serial number. If the IP address has been changed and is not known, the following steps can be taken. If you have changed the address and lost it, you can retrieve this IP address as follows: Connect a hyperterminal on the PC to one of the RS232 sockets. Configure the terminal to the following settings: baudrate 115200 bds, data bits 8, parity: none, stop bits: 1. Reboot the unit by switching it off and on, the IP address will be broadcasted by GAPS on the hyperterminal.

How should I set the blanking time on my GAPS for the best performance?

In order to get the best responses from your Beacons, you must always set a blanking time based on the recurrence you have set in the GAPS. The blanking time must always be -200ms from the recurrence of the interrogations from the system. For example, if the recurrence is set to 1s, then you must configure the blanking time to 0.8s. Refer to GAPS user manual for detailed tables for different examples.

What is the recommended procedure for GAPS hydrophone maintenance?

For preventive maintenance
In order to limit growth on the hydrophones, IXBLUE recommends to use the following anti-fouling:
International: TRILUX 33
SigmanCoatings: blue Sigma-glide
They should be cleaned with isopropylic alcohol (Steps mentioned below)
Light abrasions with 100/120 sand paper
Clean with isopropylic alcohol
Wet the surface with aliphatic hydrocarbon solvent
Wait for 2 minutes to dry
Apply anti fouling according to the manufacturers recommendations (a thin coating)
Wait for 24 hours
For curative maintenance:
To clean the hydrophones, use synthetic soap and water
To remove growth, use 180 sandpaper and apply minimal pressure on the hydrophone

What should be the maximum voltage when my MT9 beacon is fully charged?

The level of the battery pack when fully charged should be around 8.5V (between 8.4V and 8.6V)
The battery voltage level can be requested via the following steps:
1-Disconnect any external charger
2-Connect the transponder to the PC through the connection box
3-Launch the Transponder HMI interface
4-Press the F1 key
5-In the command utility window that appears, click Diagnostic button to display the battery voltage.

What is the minimum voltage for an MT9 beacon to be operational?

The MT9 does not operate when the battery voltage is lower than 7V.

How should I configure my MT9 interrogation codes for responder mode?

You must apply the same interrogation code to both responder and transponder modes in the configuration software.
If your responder signal is not sent to the beacon (in case of a cable cut), the beacon will automatically move to transponder mode. In this case it is necessary to have the same interrogation code so that you can continue to follow your beacon. Bear in mind that it will be necessary to change the configuration of GAPS when the responder signal is no longer being sent.

What is GAPS positioning accuracy ?

GAPS positioning accuracy depends mainly on Signal to Noise Ratio.
This Signal to Noise Ratio depends on the beacon transmit level, the range to the beacon, the noise level and the vertical angle
. In best case (SNR_in > 20 dB and in vertical conditions), the positioning accuracy is 0.06% of the slant range (CEP-50). i.e. 60 cm accuracy at 1000 m of distance.
If SNR_in is 10 dB, the positioning accuracy is 0.17% of the slant range (CEP-50).
For low SNR (around 0 dB), the positioning accuracy is 0.5% of the slant range (CEP-50).
When tracking horizontally, the positioning accuracy is 3 times less.

What is GAPS maximum range?

The maximum range is dependent on the noise level and the beacon transmit level. For a TL = 191 dB ref µPa:
- if noise level is 60 dB ref µPa: max range is 5000 m (example of buoy installation - SEA STATE 6 + 10 dB)
- if noise level is 70 dB ref µPa: max range is 3600 m (example of quiet vessel)
- if noise level is 80 dB ref µPa: max range is 2300 m (example of a vessel manoeuvring, GAPS at a reasonable distance from the thrusters)
- if noise level is 90 dB ref µPa: max range is 1300 m (example of a vessel manoeuvring, GAPS very close to the thrusters)

What is the longest available cable for the GAPS NG?

The GAPS NG cable can be a maximum of 95m in length due to the Cat 5 Ethernet maximum length limitation. If longer distances are required between GAPS head and GAPS box, it is possible to connect 2 x 95 m cables through a repeater box (total length is then 190 m).

How accurate must my GPS lever arm be?

Try to use lever arms 10x as accurate as your measurement. For example, within 10cm for a 1 m accurate GPS. This will ensure your lever arms will not affect the performance of your system.

Where is the reference point of the GAPS?

The reference point of the USBL is the SUBCON connector, on top of the GAPS head.

Why is GAPS the most suitable system for shallow water?

Because of its specific antenna composed of 4 hydrophones, that form a tetrahedron. This is a 3D antenna than enables positioning of a beacon with good accuracy on 3 axes (X, Y and Z). The Gaps has an aperture of 200°, which means we can track a beacon less deep than the antenna.

Which Navigation Softwares are compatible with GAPS?

Almost all navigation softwares have GAPS driver (QINSY, NAVIPAC, HYPACK, STARFIX, WINFROG, GECDIS). If your navigation is not in this list, GAPS can emulate third party protocols (GPGGA, SONARDYNE, KONGSBERG) In most cases, GAPS must not be declared as a standard USBL system because this is a pre-calibrated system. In QINSY for example, GAPS must be declared as a positioning system.

Do I need to measure the sound velocity profile?

To obtain GAPS' nominal accuracy, the measurement of the sound velocity in the water column is mandatory. If the sound velocity profile is not measured and not configured into GAPS, this can lead to inaccuracy and even to non positioning. If no sound velocity probe is available on the vessel, statistical sound velocity profiles can be used. Contact IXBLUE to get a statistical sound velocity depending on your location and season.

How to optimize GAPS performances?

The different possibilities are:
- increase beacon transmit level
- reduce noise received by the GAPS (increase the horizontal distance between GAPS and source of noise, increase GAPS depth)

What to do if positioning accuracy is not as good as expected?

If positions are jumpy, this probably comes from a multipath (reflective surface which is to close to the GAPS or the beacon) and/or difficult conditions for acoustic propagation (shallow water or horizontal tracking). Increase GAPS depth or place the beacon transducer differently.
If a bias is observed in the positioning:
- check beacon turnaround time (in the beacon and in the GAPS web MMI)
- check that a correct sound velocity profile has been configured into the GAPS
- check the GPS lever arm and potential mounting misalignments

What comes in a standard GAPS delivery?

GAPS standard package comprises the GAPS head, a 50 m cable and the GAPS box. Beacons, other cable lengths, GPS antenna can be ordered separately.

What operating system does GAPS support?

GAPS is operated through an Internet browser (Firefox, Chrome, Internet Explorer, Safari…) and operated from any device that runs an Internet browser (laptop, workstation, computer, mobile, tablet...). This means that there are no restrictions regarding the Operating System. iXblue recommends the use of Firefox because this is our qualification environment.

What is the best location to mount the GAPS head?

As far as possible from any source of noise (thrusters, propellers, engines...) and below the wash created by the thrusters.

What is the best location to mount the beacon on ROV?

As far as possible from any source of noise (thrusters, propellers, engines...) and on top of the ROV in order for there to be direct acoustic line of sight between the GAPS head and the beacon transducer.

What is the impact of GAPS mounting misalignments (heading, roll, pitch) ?

If the GAPS to GPS lever arm is small (< 5 m), GAPS mounting misalignment has low impact.
If the GAPS to GPS lever is larger, it may have an impact and it is recommended to enter these misalignments into the GAPS web MMI (mechanical installation parameters).
These misalignments can be estimated at sea (when INS correctly aligned) by comparing GAPS heading roll and pitch to vessel heading roll and pitch.

Do third party beacons have the same positioning performances compared to iXblue beacons?

Each type of beacon has its own characteristics (transmit level, directivity, type of signal). Positioning performances are therefore different from one type of beacon to another.