AUTONOMOUS VEHICLES (AQUATIC ROBOTS) USED IN MONITORING AND DETECTING HARMFUL ALGAE BLOOMS

There are some autonomous plate forms used for detecting and monitoring harmful algae bloom. These plate forms can be equipped with a wide range of sensors and varying levels of autonomy. Environmental sensory networks will often employ a combination of severs different plate forms to achieve the best results (Mellinger, 2012). Some of this autonomous

plate forms are: Autonomous under water vehicles (AUVs), Autonomous surface vehicles (ASVs), Unmanned aerial vehicles (UAVs), sensors etc.

2.1 Autonomous Underwater Vehicles (AUV)

Autonomous underwater vehicles (AUV) are remarkable machines that revolutionized the process of gathering ocean data. AUVs come on multiple shapes and sizes to fulfill a wide verity of roles from oceanographic data collection to ship hull inspection the torpedo AUV is the standard design for oceanographic work where straight line performance is prioritized over maneuverability (Lucieer, 2011). This robotic device is driven through the water by a propulsion system, controlled and piloted by an on board computer. Sensors on board the AUV samples the ocean for harmful algae bloom as AUV mores through it, providing ability to make both spatial and time sense measurements AUV travels underwater without requiring input from an operator. With miniature sensors and computers allow the AUV to be equipped for missions on including undersea archeology and exploration, environmental monitoring and acoustic surveillance (Lucieer, 2011). The AUV from ocean server are primarily used for measuring water properties with their in-situ chemical sensors. The chemical sensors on the AUV are able to measure turbidity, dissolved oxygen, rhodamine, chlorophyll, blue-green algae (phycoerythin), pH, temperature and salinity. One man-portable ocean server 1yer 2 a six diameter torpedo shaped and found at on end of the can operate for several hours in shallow (<100m) coastal waters while equipped with standard sensors such as a CTD or ADCP. At the other extreme are deep water AUVs capable of operating several thousand milers deep for a day or more, these AUVs can carry advanced button scanning sonar or tow multi-transducer arrays (Curton and Bellinghan, 2001).

2.2 Autonomous Sure Ace Vehicles (ASVs)

Autonomous surface vehicles (ASVs) are for operations in habours, lakes and shallow coastal zoned. They provide pay load and computation capabilities similar to larger AUVs while being much cheaper and easier to operate capable of speeds of several meters per second, they can operate on much stronger currents than many AUVs (Achtelik, 2009). Their case of use combined with availability of RF communications also makes then an ideal plate form for the development of control and autonomy software. The ideal of monitoring several metes of ocean water with AUVs and UAVs in constant communication led the development of swordfish ASV. The scout (surface craft for ocean graphic and under a testing) is an ASV built around a standard kayask hill. Initially developed at MIT on 2004, the scout was designed independently or in conjunction with AUVs (Curcio, 2005). It has since been commercialized  and had been used in wide variety of field trials from ocean graphic studies to experimental hydrodynamic research (Zheng, 2009). Equipped with a winch, the vehicle can deploy oceanographic sensors a various depths a providing an AUVs data product for shallow waters without the usual hassle and expense (McGillivary et al., 2006).

2.3 Unmanned Aerial Vehicle (UAV)

Unmanned aerial vehicle (UAV) can fill the gap between remote sensory satellite systems and in-site observation plate forms. They can also provide surveys of inaccessible or rough terrain UAVS can target biosecurity application that can be observed only above or that require sampling of areca environment.  

The primary types of UAV are fixed wing rotary wing and lighter than air (LTA). LTA autonomous airship have potentially the longest mission times and can have for extended periods of time over an area of interest, however they more at slow speeds than air planes or helicopter. Fixed-wing UAVS tend to be the fastest alternative and here potentially the longest mission range but can neither hover not operate very close to the surface. Helicopter, due to their high controllabity, can be used for prose nap-of-the-earth flying as well as hovering but have shorter mission time and  ranges UAU plat forms for civilian use cost typically one to two orders of magnitude less than manual aircraft in their category and are also much chapter to operate. As a result UAVs are being deployed in increasing numbers around the world for a growing number of applications. UAVs operate over a spatial scale of the order of 1-10  resolution of centimeters to tens of meters depending on the flight altitude and the sensor pay load. All three of UAV can perform surveys of areas of interest at regular time intervals (typically minutes to hours) and airships and rotary-wing craft can hover over a given area for longer prior as of time to allow persistent temporal monitoring of a process of interest. Sensor pay loads on UAVs for biosecurity survey can red-green-blue (RGB), thermal, multispectral and/or hyper spectral imaging sensors, lidars and/or radar for characterization of the 3D environment below the aircraft environmental and weather sensors and a combined GPS and inertial navigation system (INS) unit for accurate localization of sensor observation. High value applications of UAVs in biosecurity survey such as limonlogical and var-shove ocean surveys for harmful algal blooms (HABS).

2.4 OPERATION OF AQUATIC ROBOTS AUTONOMOUS VEHICLES

These aquatic robots can be instrumental in detecting occurs suns of invasive species into protected area, either organically over time or through attachment to the halls of ships that travel from other area where species is prevalent. Aquatic robots can deployed for standalone tasks such as ship hall inspection reef monitoring by common wealth Scientific and Industrial Research Organization (CSIRO) star bug or sample collecting by Monterey Bay Aquarium Research institute (MBARI) Gulper or be used along side static sensor net works such as data mules and mobile  nodes with high-value sensor payloads. A CSIRO ASV can be used as a mobile node for water quality monitoring to detect HAB in water storage reservoir connected to a longer, floating static sensor network. Aquatic robots can carry underwater vision and sonar sensors to detect and characterize submerged biosecurity threats. Although most shallow water biosecurity surveillance is currently being done by divers, robotic solutions based on Remotely operated vehicles          are now emerging for submerged biosecurity threats. Although most shallow water biosecurity surveillance is currently being done by divers, robotic solutions base on Remotely operated vehicles             are now emerging for submerged port inspection and in-water ship hall inspection and applications, to prevent the introduction of invasive species  R     can operate at almost any depth, perform in high-resolution survey of an area of interest and perform interventional tasks. However, these require permanent connection to a surface vessel or larger AUV by a tether, constraining their maximum operation range, as in the case of the Roving Bat.

AUVS are more suitable for tracking biosecurity event as they can cover a spatial scale of the order of 1-20km2 in range with a resolution of few centimeters and do not require tethering to another vessel, allowing them to freely maneuver during a mission. They can explore the seafloor with no gaps in deep or shallow water, to onset submerged structures or ship hills, take samples of harmful algae blooms. AUV mission duration is usually constrained by their endurance. Glider-type                     

Table 1: Mission parameters for study of algal blooms by a UAV.

Parameter Algal blooms

Parameter	Algal blooms
Knowledge goal	· Determine the existence and location of potential algal blooms · Direct the deployment of AUVs and ASVs for in-situ measurements · Secondary data product
Target characteristics	· Bloom’s location, size, and temporal aspects all unknown · Best identified by some color variation
Measurement characteristic	· Visual spectrum ·Looking for meta-scale properties such as color contrast
Operator interaction	· Define search area · Providing visual feedback via identification · Behavior modification after discovery
Coverage and navigation requirements	· Rapid coverage of large areas · Low spatial accuracy required
Data processing	· Mosaicking based on navigation data · Limited image processing for partial bloom recognition

2.7 EXISTING WORK IN SMALL AERIAL VEHICLES 

The increased availability of small, low-cost autonomous and remote aerial vehicles has seen a surge in their use for various research and remote sensing applications. More advanced control methods for careful trajectory following and maneuvering have been explored under controlled environments where precision position sensing is available via a video tracking system or similar (Mellinger, 2012). Simultaneous localization and mapping (SLAM) has been very successfully implemented in indoor environments using laser scanners and cameras (Achtelik, 2009). Outdoor environments provide additional challenges including wind disturbances and larger scale environments that may challenge SLAM algorithms, though recent work has focused on improving the autonomous operation of quadrotors in feature-rich outdoor environments (Wendel, 2011). Remotely-operated aerial vehicles with little or no built-in autonomy are commercially available through several manufacturers and used not only for research, but also aerial reconnaissance by law enforcement agencies, rescue services, and others. 

The application of an autonomous aerial vehicle to marine environmental sensing presents challenges most similar to those tackled by remotely operated commercially operated vehicles. The environment is very feature-poor, and hence not amenable to the large body of research available for navigation and control of quadrotors in a more controlled environment (Achtelik, 2009).  The desired operation ranges also greatly exceed those typically supported by commercial systems, which typically rely on the vehicle remaining within eyesight of an operator. The unique marine environment exposes the vehicle to harsher external conditions, primarily wind, and imposes a very high penalty, complete loss, for any system failure, whether it be in software or hardware (Achtelik, 2009).

2.8 SENSORS 

The sensors described here are just a few of the most common sensors typically found on autonomous marine platforms. 

2.8.1 Conductivity, Temperature, and Depth (CTD) Sensors: 

Possibly the most common instrument used in oceanographic experiments, a CTD can measure water temperature, salinity, and density. Modern CTDs are small enough to be mounted on almost any vehicle while still providing excellent accuracy. A CTD is usually the first step in studying any environmental phenomenon. Additional sensing capabilities for parameters such as pH and dissolved oxygen can also be built into CTD instruments (Achtelik, 2009).

2.8.2 Mass spectrometers and flourometers:

 At their most fundamental level, mass spectrometry is used to measure the mass-to-charge ratio of charged particles and determine elemental composition or the chemical structure of molecules. Underwater mass spectrometers provide this functionality in a small package that operates on samples of water, usually provided by an internal pump and filter apparatus (Boykov, 2001).  They are useful for identifying low molecular weight hydrocarbons and volatile organic compounds associated with pollutants. Flourometers perform similar measurements by examining the intensity and wavelength of electromagnetic emissions from a sample after excitation. They identify higher molecular weight compounds including organic entities such as chlorophyll. Together the two techniques can give us a more precise picture of the various chemicals present in a water sample (Curcio,  2005).

2.8.3 Acoustic Doppler Current Profiler (ADCP): 

An ADCP can perform remote current measurements by sending acoustic pulses and measuring the Doppler shift in the return reflected by particles in the water. Through the use of multiple beams, an ADCP can determine the three-dimensional current flow at multiple distances from the sensor. Range can vary from just a few meters to hundreds of meters, with accuracy typically decreasing with range as lower frequencies must be used. ADCPs are frequently mounted facing downwards from an AUV or surface vehicle to measure current throughout the water column (Curcio,  2005). Some units can also function as a Doppler Velocimetry Logger (DVL), locking onto the seafloor and measuring the velocity of the vehicle rather than water currents (Curcio,  2005).

2.8.4 Imaging sonar: 

While less applicable to environmental sensing, imaging sonars still bear mentioning here because of their widespread use on underwater vehicles. Side-scan sonars are commonly used on AUVs or towed behind surface ships to image a wide area of seafloor to either side of the vehicle. Varying frequency, usually in the several hundred kilohertz range, provides a tradeoff between swath width and resolution. Other types of sonar are designed to more accurately image smaller areas or even characterize the sediment or rock under the seafloor (Curcio,  2005).

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