Author: Ioseba Tena – Global Business Manager – Marine Robotic Systems
In mine clearance operations, time is one of the most critical factors. It can determine the success or failure of a mission.
In times of conflict, your amphibious fleet could be stranded at sea while your mine clearance operations are carried out. The time lost could be the difference between mission success or failure. Even in peacetime, when time constraints can be relaxed, clearing an area of legacy mines from a prior conflict is an expensive, complex logistical endeavour: it ties up resources; it puts personnel at potential risk; and, as days accumulate, costs mount.
In a busy commercial shipping channel, mine clearance operations could cost millions in lost trade for every day spent detecting unexploded ordnance (UXO). Whichever way you look at it, mine counter measure (MCM) operations need to be done quickly. They also need to be done right.
Unmanned maritime systems (UMS) have helped expedite MCM operations, particularly in very shallow waters (VSW). Autonomous underwater vehicles (AUVs) are routinely mobilised to survey the shallowest littoral waters to detect and classify targets. Divers or small remotely operated vehicles (ROVs) are then used to identify and neutralise contacts.
Today, small, two-man portable AUVs are deployed from rigid hulled inflatable boats. Their missions are pre-programmed, following predetermined waypoints, to gather data using a side scan sonar, which an operator then analyses to find mines. ROV pilots or diving teams then locate, identify and neutralise the target.
AUV missions can be sped-up by using longer range sensors. But, these are often larger, require larger AUVs and result in more complicated logistics. You can also work on the time it takes to analyse the data. This is a monotonous and error-prone task currently undertaken by human operators. Miss-classifying a contact can lead to a wasted dive and providing an inaccurate estimate of the contact’s location can lead to time wasted searching for where the mine should be.
So, how can we improve the accuracy of our surveys, and speed up the analysis and reduce error rates?
I’ve said it once and I will say it again: it’s all about the data. Our Solstice is an incredibly compact but also high resolution Multi Aperture side scan sonar, with a low power budget, that can be used to significantly improve the effective mine-hunting range of two-man portable AUVs. With it, more data can be acquired sooner and at better resolution.
Then, add our Automatic Target Recognition (ATR) algorithms to its capabilities and it will offer a further leap in capability, massively reducing the time it takes to detect and classify potential threats. ATR will assist AUV operators to classify mines faster by pre-analysing the data and providing an overview of all the mine-like contacts that were acquired. Half the job is done for the operator before they even start their work. No need to wait for mission reports. Our aim is to have mine clearance AUVs that automatically report any contacts as soon as they get recovered.
We can also reduce the errors in locating mines. Positional accuracy is a challenge for AUVs. They operate underwater, where there is no equivalent to the global navigation satellite system we use on land. To maintain their position, AUVs have to surface. As soon as they dive, they have to rely on dead-reckoning and are effectively lost. It’s just a question of how lost. Dead reckoning works by estimating position based on the direction of travel and speed of travel over time. Typically, an AUV gets this information using a number of sensors:
– A Syrinx Doppler Velocity Log (DVL), which measures the Doppler shift on acoustic waves bouncing back from the seabed.
– A SPRINT Inertial Navigation System (INS), which is used to fuse the data from a block of gyroscopes and accelerometers with the other sensors to work out the AUV’s position.
With these instruments on board, the AUV’s estimated errors will grow as a function of distance travelled. That means that as time passes you will have poorer estimates for the position of the mines you encounter. In clear, bright waters you may be able to live with that. But, at night, or in poor visibility, even a small position error can add substantial time to your diving operations.
Using Ultra-Short Baseline (USBL) positioning helps. Acoustics can be used to send position fixes to the AUVs from a surface vessel or an Unmanned Surface Vessel (USV); a simple fix if you can entertain being on the surface with a USBL system while the operation is running.
There’s now an alternative: hybrid navigation. We have developed a hybrid navigator, SPRINT-Nav, which tightly integrates all the raw sensor data at a low level to provide unprecedented improvement in self-contained or ‘dead-reckoning’ navigation accuracy and reliability. The accuracy is so high that many missions can now be performed without any assistance from surface vessels while achieving accuracies two to five (and more) times better than separately integrated instruments at the same cost. This is a true enabler for covert, accurate MCM.
Time is critical and accurate maps means less time and money wasted and your assets are better utilised. You can minimise the time from detection to neutralisation. You can combine hybrid navigation instruments with class leading seabed imaging. This technology is available today. The cost is comparable to other systems already in use that provide less accurate pictures and higher navigation errors. Want to find out how to increase your AUV’s Area Coverage Rates and build more accurate maps, faster? Please get in touch.