Sentinel FAQs


Questions about general usage

The Contracting Authority is interested in deploying an intruder detection sonar system in two seaports. One will have to be mobile, given the size of the port. The other one will be at a fixed location. To what extent is a mobile system also capable of functioning in a fixed location?

The Sentinel system is very adaptable. The portable unit can be deployed on a seabed tripod for semi-permanent deployment, mounted on a vessel to provide mobile cover, or mounted to a fixed deployment structure for a permanent solution.

How many personnel and how much time is required to install and remove a mobile intruder detection sonar setup?

The Sentinel can be deployed by as few as 2 employees and deployed/recovered within a few minutes depending on deployment method.
As an example some current clients utilise a RIB to deploy and move a portable Sentinel system.

The performance of the intruder detection sonar system can be affected by external forces. The systems will be deployed in busy seaports with constant traffic. To what extent should this be considered?

The Sentinel system is designed for use in typical harbour environments, where there will be reverberation from structures, and interfering noise from machinery etc. The use of FM replica correlation and beamforming give large processing gains against interference, and the system has been shown to work reliably in these environments. However we also provide two main methods to monitor the effects of the environment on the performance of the sonars. First we provide an advanced acoustic performance prediction tool which gives an estimate of performance based on measured sound speed profiles and background noise. Secondly, the system has a built-in performance monitoring system which measures the interfering noise and reverberation, and indicates which directions may be seeing high levels of interference.

For practical use, it must be possible to view the system’s information remotely (i.e., not via a cable). For example, on a screen in a control room. The information transfer must also be secure. To what extent is this possible?

The system displays may be remote from the system, and can be connected via KVM switches over wireless Ethernet if required. Alternatively the system may be viewed and controlled via secure encrypted remote desktop application over an Internet connection. The system also has an external interface over Ethernet LAN to a Command and Control system, and all data (sonar imagery, tracks data, system status) is available over this interface. This interface may also be encrypted.

Questions about technical features

What is the minimum and maximum water depth for the correct operation of diver detection sonars?

The sonars should generally be installed at depths between 2m and 30m; we provide guidance on the optimum deployment depth based on the local environment (particularly water depth and sound speed profile). The sonars can detect and track when looking into water as shallow as 1m, though we do not recommend installing the sonars in less than 2m (and deeper for tidal areas). The maximum depth the sonar will detect and track is very dependent of the sound speed profile at the installation site. In isovelocity conditions in very deep water (>>100m) the vertical field of view of the sonar will give coverage to up to 100m depth. However this may be less if the sound speed profile results in upward refraction.

What are the minimum and maximum temperatures for the correct operation of intuder detection sonars?

The sonars can operate in water temperatures between -10 and +40 deg C.

What is the average underwater area that can be adequately monitored with an intruder detection sonar?

The area coverage varies depending on the local environmental conditions (primarily water depth, sediment type and sound speed profile). In cooler climates such as Europe we typically expect around 600m range, which equates to a circle of area 1.13 km². In good propagation conditions we can achieve up to 900m range against divers (2.54 km²).

To what extent are intruder detection sonars resistant to strong currents and passing ocean-going vessels?

When permanently installed on seabed stands or fixed to jetties, the sonars are not damaged by strong currents or passing vessels. Generally currents do not affect detection performance; however strong currents can result in floating debris moving through the sonar field of view in a similar way to threat targets. Sentinel has special software to identify and ignore tracks generated by current-driven targets.

For practical use, a mobile setup must function without a direct connection to an electrical grid. To what extent is this possible? What must be taken into consideration for such a setup?

We have a version of the expeditionary Sentinel system which can be run from 24V DC batteries.

Questions about maintenance

How does salt water affect the maintenance of an intruder detection sonar?

The sonar heads are designed for permanent immersion in salt water. The only maintenance of the sonar head required is to periodically clean to remove bio-fouling. We have an expeditionary IP67 rated system in which the topside is resistant to salt-laden atmosphere.

Is it possible for in-house maintenance staff to carry out maintenance on intruder detection sonars? If so, what is the required level of knowledge and experience for such an employee?

Yes. The only scheduled maintenance task is periodic cleaning of the sonar heads, which can be done by in-house staff. Repair is by replacement of LRUs. The system has built-in test which indicates the health of the system, and with remote support by Sonardyne/Wavefront it is normally simple for in-house staff to replace LRUs.

What is the expected lifespan of an intruder detection sonar?

The design life of the system, with maintenance, is 20 years.

For practical use it may be necessary to adapt a system to a new environment. For example, if the new environment leads to false alerts. To what extent is it possible to manually adapt the system to minimise the number of false alerts?

The system is very flexible for exactly this type of requirement. The detection parameters and the track filter settings for the multi-level alerts are very flexible and can be changed by the user to adapt to new environments, thereby reducing false alerts. The system also has a high degree of automatic adaption; for example the detection threshold automatically adapts to changes in the environment.