UDT 2020 Remote Mine Identification from Man-Portable UUVs 2G Robotics Remote Mine Identification from Man-Portable UUV’s Chris Gilson 1 1 Product Development Manager, 2G Robotics, Waterloo Canada – cgilson@2grobotics.com Abstract — Unmanned Underwater Vehicles (UUVs) are becoming the platform of choice for modern mine countermeasure (MCM) operations. Advantages of reduced platform cost and improved mission efficiency are already being realized through their use for mine detection with side-scan sonar. However, for UUV’s to reach their full potential they must be able to perform remote visual identification in order to reduce the frequency of clearance diver deployments into the minefield. This paper discusses the challenges associated with developing a camera payload for man-portable UUVs, including power constraints, imaging at high speed, turbidity, size limitations, and data workflow. An MCM operational process is outlined for using such a system to conduct Remote Mine Identification after detection and localization of mine-like- objects (MLO) is completed with a side-scan sonar survey. Using the 2G Robotics Mine Identification Payload on Hydroid REMUS vehicles, it is demonstrated that high-resolution stills image data can be used to obtain visual identification of mine targets with a high degree of confidence. Automated software is employed to use side-scan sonar target files to efficiently extract target data from large image datasets in order to increase the operational tempo of MCM missions. High resolution camera payloads deployed on man-portable UUVs have the potential to improve MCM mission efficiency and reduce risk by limiting the time that divers and vessels are in the minefield. Continued operational testing by the REMUS users and the MCM community will determine whether this solution will become a standard part of modern mine countermeasure operations. 1 Introduction laser data to reduce the risk of missing critical defects [2]. In this application, laser and image data have enabled the Unmanned Underwater Vehicles (UUVs) are rapidly adoption of automated data analysis where pipeline defects becoming an essential platform for modern mine can be identified automatically. Machine vision is used to countermeasure (MCM) operations. Their adoption offers detect and highlight features of interest, reducing the increased operational efficiency, reduced platform cost, amount of data that an operator must analyze manually and and a reduction in risk by removing personnel and vessels significantly reducing data analysis time. from the minefield. However, to truly change how MCM operations are executed these vehicles must evolve to offer This paper outlines the development challenges and trade- Remote Mine Identification capability that reduces the offs associated with miniaturizing the 2G Robotics camera reliance on clearance divers for performing visual system for use on smaller man-portable platforms. The identification. development is based on the proven 2G Robotics ULS-500 Micro product shown in Figure 1 below. It consists of a An MCM operation consists of 4 stages: Detection, high-resolution stills camera, high output LED panel and Classification, Identification, and Disposal/Neutralization capacitor bank, onboard processing computer, and subsea [1]. With today’s UUV platforms, mine detection is laser scanner. completed using side-scan sonar and, in some cases, classification can be achieved using high resolution synthetic aperture sonar (SAS). However, a vessel must then enter the minefield to deploy a clearance diver or a remotely operated vehicle (ROV) to complete the visual identification stage. This is particularly time consuming in areas with complex seabed since the limited resolution of sonar leads to a high probability of false detection and Fig. 1. 2G Robotics - ULS-500 Micro . therefore many unnecessary diver deployments. Development and testing was conducted on the Hydroid The commercial sector has proven that sonar data can be REMUS 100 and REMUS 600 vehicles. The REMUS 100 augmented with high resolution optical data to reduce the is a man-portable sized 7.5 inch diameter UUV used by a uncertainty involved in underwater sonar surveys [2]. This number of navies including the Japanese Navy and US is particularly relevant for subsea oil and gas pipeline Navy (designated Mk 18 Mod 1) inspection where multibeam sonar on UUVs has been supplemented with and high-resolution images and 3D
UDT 2020 2G Robotics Remote Mine Identification from Man-Portable UUVs LED strobe power consumption is defined by the camera frame rate (Hz), LED output intensity and the camera exposure time (ms), as shown in the below equation. Minimizing each of these factors was explored in the Fig. 2. Hydroid REMUS 100 system design to reduce power draw, while simultaneously trying to maximize the lighting output efficiency of the The REMUS 600 is a mid-sized 12.75 inch diameter UUV system. used by a number of navies including the UK Royal Navy and US Navy (designated Mk 18 Mod 2) Power draw ∝ Frame Rate x Intensity x Exposure time (1) To reduce the required frame rate, a dome viewport was integrated into the camera module to increase the along- track field-of-view to 63 degrees. This allows for a frame rate of less than 1 Hz to be used while still achieving a 45% Fig. 3. Hydroid REMUS 600 overlap on successive images when operating at 3 meters altitude and 4 knots speed. The dome viewport also Testing was aimed at evaluating the capability of the Mine provides a significant improvement in UUV coverage rate, Identification Payload on small UUV platforms for delivering an across-track field-of view of 80 degrees. performing visual identification of mine targets. With typical flat viewport cameras requiring 2 Hz Specifically, the aim was to determine if this optical operation for complete coverage, this reduces payload payload could successfully identify MLOs with the same power draw by a factor of 2. In addition, the camera level of certainty as a clearance diver. The Mine resolution was increased to 12 megapixels from a standard Identification Payload includes a stills camera and high 5 megapixels in order to maintain the same effective target power LED panel to capture 12-megapixel (4K) resolution resolution with the larger field-of-view. images of targets with even illumination and high contrast. Imaging can take place at long ranges up to 7 meters Most high output LED arrays available on the market emit altitude and at speeds of up to 4 knots. The payload white light, which are not power efficient due to water incorporates an on-board computer for real-time image absorption. The graph shown in Figure 4 shows the enhancement and stores images either on a local hard-drive increasing water absorption of light with increasing or an external removable storage device. wavelength, with blue having the lowest absorption coefficient. White light consisting of all wavelengths is inefficient at delivering the generated light to the camera 2 Development & Challenges sensor since the higher wavelengths are rapidly absorbed and do not reach the camera. When a monochrome camera The development of a camera system for man-portable is employed, it is possible to use a light source with a UUVs presents various technical challenges that were specific wavelength to optimize the system for optical overcome to deliver high quality images. These challenges transmission in water. To take advantage of this, custom and the resulting design solutions are outlined in this blue LED arrays were designed which deliver the same section. effective light transmission to the camera as a white light but consume significantly less power. 2.1 Power Constraints Small UUVs have a significantly lower power capacity than larger vehicles that have historically used high resolution optical payloads (eg. REMUS 100 has 1 kW-hr battery capacity compared to 62.5 kW-hr on a HUGIN Superior). With this constraint in mind, the power draw design requirement was defined as a maximum average power draw of 50 watts which ensures the vehicle maintains a usable endurance level. This limitation required significant changes to the 2G camera system which are discussed below. The largest contributor to power draw in a camera system is the artificial light source. For this reason, an LED strobe was selected instead of a continuous light source in order to reduce power draw. A strobe lighting system is designed with a capacitor bank that draws consistent power from the vehicle battery to charge up capacitors that deliver the accumulated power in short, high-intensity bursts via the LEDs. This allows for very high light power (>200,000 lumens) to be output during short camera exposure times. Fig. 4. Light Absorption Coefficient of Water
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