# AUV Adaptive Sampling Methods: A Review
## 2 Process of Adaptive Sampling
The ultimate objective of this step is to make the best decisions to autonomously serve the end goal via processing sampled information. Diagnosis is crucial, but challenging, as it requires the ability to analyse and interpret the collected measurements through associated data. This is especially true when the measurements are not straightforward and require further processing to turn them into useful information. The collected in-situ measurements should usually undergo several processes prior to making any decisions by the AUV. Firstly, the obtained measurements are processed using a certain type of filter as all sensor measurements in robotics are raw, imperfect and subject to errors. A substantial amount of sensor noise makes the measurements less reliable. Such ambiguities and uncertainties (in vehicle motions and sensor measurements) are an inherent issue in robotic missions. Therefore, a probabilistic approach is usually taken as a solution, as opposed to a deterministic approach (e.g., [1]). Secondly, onboard analysis capability in modern AUV technology enables sensor readings to be converted into \begin{table}
\begin{tabular}{c c c} \hline \hline
**Marine Phenomena** & **Detection Parameter** & **Sensing Instruments** \\ \hline Thermocline, Internal waves, River plume & Temperature, Conductivity, Pressure & Conductivity, Temperature and Depth (CTD) sensor \\ \hline Upwelling & Temperature, Salinity, Chlorophyll-a fluorescence & CTD sensor, Fluorometer, Backscatter sensor \\ \hline Harmful algal bloom, Phytoplankton & Chlorophyll-a fluorescence & Fibre Optic Fluorometer, Optical plankton discriminator \\ \hline Chemical plume, Produced water & Salinity, Turbidity, Dissolved O\({}_{2}\) concentration & CTD sensor, Wet chemical analyser, Mass spectrometer (MS) \\ \hline Hydrothermal vent plume & Temperature, Particle contents, Current velocity, Bathymetry, Chemical components. & CTD sensor, Optical sensors, eH (redox potential), ADCP, Side scan sonar (SSS), Multibeam sonar \\ \hline Hydrocarbon plume & Dissolved O\({}_{2}\) and CO\({}_{2}\), CDOM fluorescence, Particle size, Polycyclic aromatic hydrocarbons & Optical light scatter, CDOM fluorometer (CF), Electro chemical sensor, Mass spectrometer (MS), Laser in-situ scattering and transmissometry (LISST) sensor, Fibre optic chemical sensor (FOCs) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sensors to be integrated with an autonomous underwater vehicle (AUV) for sampling the physical, biological and chemical features discussed in this paper. meaningful data values that can be used in decision autonomy. How adeptly an AUV can perceive its own state and its environment relies on data analysis and the analytical algorithm design. They can vary from a binary structure, which simply defines the presence or absence of a phenomena of interest, to a wider range of state estimates, which leads to a consequent action to be taken in the next step. Appropriate thresholds are often requisites for successful diagnosis. They represent the adequate level at which scientists believe the measure is worth sampling. Threshold values can be unit or unit-less scalar attributes such as temperature (\({}^{\circ}\)C), concentration (mg/L, ppb), number of particles, salinity (ppt) and water velocity (m/s). They could also be instantly calculated values such as gradients. The values are given from the beginning of a mission if the survey area is sufficiently known or if the mission goal is to seek the location of the target thresholds in particular. Variable thresholds, on the other hand, consistently change and provide a high level of flexibility in terms of survey range, especially in the early stage of the event, where there is limited basic information available [4]. Adaptation: The last segment, _adaptation_ takes charge of executing adaptive commands and the calculated value is delivered to the actuation system. The adaptation commands include redesigning the mission plan, modifying the survey pattern and updating the vehicle trajectory.