FAQ

Is GIB a long baseline system?

In some ways the GIB system is similar to a long baseline system. It is sometimes referred to as surface long baseline as the reference points are buoys anchored or drifting on the surface.
GIB, like a long baseline system, uses the principle of measuring the propagation time of an acoustic pulse between a mobile transmitter and a receiver. However, when you use a standard long baseline system to track a vehicle from the surface, you will require 6 successive acoustic paths:

  • ship interrogating the seabed transponders;
  • transponders replying to ship;
  • ship interrogating the underwater mobile;
  • mobile replying to ship's interrogation and interrogating transponders on the seabed;
  • transponders transmitting to the ship.

That's a long and error-prone process!
GIB, on the other hand, is a one way technique using a clock in the mobile that is synchronous with the GPS Satellites’ atomic clock.
This avoids errors in sound propagation (loss of signal or multi-path replies), providing a much higher repetition rate (1 point every second, instead of one point every 5 or 10 seconds).
Long baseline systems generally use three distances to calculate the X-Y and Z positions of the mobile. The depth value is very inaccurate when the depth is small compared to the distance between the transponders. For this reason, we have integrated a pressure sensor in the mobile's pinger. As a result, the depth telemetry technique used produces an extremely accurate estimation of depth.
Long baseline systems require a lengthy calibration step that istime consuming for the support-ship. Recovery of transponders is difficult (you don't know where they will surface).
GIB buoys do not require any calibration and are very easy to recover as their
D-GPS position is continuously transmitted to the support ship.
To summarise, GIB technology is comparable to long base line, but offers many advantages: easier to deploy, lower cost, higher repetition rates.

How many buoys do I need?

Just like a long base line system, a minimum of two distances are required to calculate a 2 D position.
Any number of buoys from 2 to 12 can be used.
three-buoys will enable the system to calculate a mean quadratic error for each fix so that tracking quality can be estimated.

What performances can be achieved?

In D-GPS mode, the location accuracy of GIB buoys varies from +/- 3 metres to +/- 1 metre depending on the D-GPS shore station and the receiver board used.
Let us know your requirements and we will offer a suitable system at the best price.

Is it possible to compare GIB to Short Baseline Systems?

GIB, like a short baseline system, offers a solution for tracking underwater vehicles.
INSTALLATION
A short baseline system is difficult to install onboard a ship. Dry-docking is often required as well as delicate calibrations: gyro axis, short baseline transducer axis, coordinates in ship's axis, roll and pitch sensors, GPS antenna, and more!!
GIB is a very portable solution and is very easy to install. No calibration at all is required.
IN OPERATION
A short baseline system requires the ship to be above the underwater mobile, which is a major constraint for the watch officer at the bridge, especially as propeller noise will stop the system from working.
ACCURACY
Roll and pitch of the ship do significantly affect the accuracy of a short base line system. At a distance of 1 km, the short baseline system will present a dispersed cloud of points whereas the GIB will show a very smooth track.
In many circumstances, GIB tracking systems are 10 times more accurate than USBL.

Can I use standard off the shelf pingers?

Yes, most pingers can be used together with GIB buoys. However, better knowledge of hyperbolic and circular systems is required, and geometric experience is useful.
Various cases arise:
Non synchronous pingers
If at least three buoys are detecting the pinger's signals, the software will be able to calculate a position (in hyperbolic mode) but the result might be unstable in noisy environment.
To achieve better tracking stability, it is preferable to know the pinger's repetition rate with a good level of accuracy (10-6). This method assumes that the pinger has a fairly good quality internal clock. In this case pseudo-circular algorithms can be used to locate the mobile and to calculate the exact time at which the pinger transmits with respect to the GPS-UTC absolute time base reference.
In this case four buoys must be used together.
No pressure sensor
If your pinger does not integrate a pressure sensor or a depth telemetry option, you must calculate the depth of the pinger manually and enter the information into the software for slant range corrections.
In many cases this type of calculation can require a considerable effort from the operator's point of view!

Can I find a black box using the GIB technology

Yes, a Back Box lost at sea can be located very quickly (a matter of hours) using one to five GIB buoys. The buoys must be set on the proper frequency, which requires a special operational procedure and software package.
The 1-metre accuracy in latitude and longitude allows very fast recovery operations.

Will waves affect GIB systems accuracy?

Waves have two effects: firstly they generate a circular motion of the buoys; and secondly theyaffect the pinger depth measurements.

HORIZONTAL PLANE ERROR
For a wave height of 3 meters (+/- 1.5 m), the buoy's X&Y position might be affected by noise of +/- 1 m. The hydrophone 10 metres below the surface will have a heave movement of +/- 1.5 m. As the GIB system uses a long baseline, for a 750 m slant range and a vehicle navigating at a depth of 150 m, the projection of the slant range on the horizontal plane will only be affected by a 31 cm error, as shown on the table below.

 

No vertical error

1,5 m vertical error

Slant range

750,00

750,00

Depth

150,00

151,50

Horizontal range

734,85

734,54

Range difference

 

0,31


DEPTH ERROR
If you are using GIB to track a ROV or an AUV, navigating at a depth of 150 m, the wave passing above the vehicle will not modify the pressure measurement (This is demonstrated by dynamic waves propagation equation, which is an exponentially decreasing function of depth. Generally speaking, it is considered that at a depth equal to 50% of the wave length, the pressure will not be affected). Thus, the depth telemetry will still give an excellent Z value even with waves and swell.

What can I track?

So far, GIB systems have been used for highly effective tracking ofAUVs, ROVs, sonars, divers, manned submarines, torpedoes, targets or to locate black boxes pingers, dummy mines on the sea bed,
If you have other applications in mind, do not hesitate to ask us for advice.

Is it possible to have a demo?

ACSA organises demonstrations abroad on a regular basis.
We also have a demonstration base in the south of France. You are welcome to call at any time for a free demo.
If you would like to receive a report on demonstration at sea, visit our facility and / or to request a demonstration of ACSA systems, call us at +33 (0)4 42 58 59 20 or send us an email.