Submersible Sensors Research Articles

Influence of solar radiation on chlorophyll a concentration assessment using fluorescence measured by the submersible sensor in Lake Baikal

Assessment of chlorophyll a concentration based on fluorescence intensity is actively used at present. In natural waters, profile fluorescence is measured using submersible sensors. These sensors are equipped with no special chamber for phytoplankton dark adaptation before measurement. Effect of irradiance in the upper layer leads to a decrease in chlorophyll a fluorescence due to closing some reaction centers of photosystem 2. The conducted research on Lake Baikal has revealed the relationship between the share of open reaction center in photosystem 2 and photosynthetic available radiance in the lake. The relationship between these parameters was described by an exponential function with a high determination coefficient (r2=0.97). Based on the obtained relationship, an algorithm was developed to compensate for the decrease in chlorophyll a fluorescence intensity due to the light influence in situ.The algorithm enables to retrieve the “real” fluorescence profile, which is necessary for the correct retrieval of the vertical distribution of the chlorophyll a content.

Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing

Thermal response tests are used to assess the subsurface thermal conductivity to design ground-coupled heat pump systems. Conventional tests are cumbersome and require a source of high power to heat water circulating in a pilot ground heat exchanger. An alternative test method using heating cable was verified in the field as an option to conduct this heat injection experiment with a low power source and a compact equipment. Two thermal response tests using heating cable sections and a continuous heating cable were performed in two experimental heat exchangers on different sites in Canada and France. The temperature evolution during the tests was monitored using submersible sensors and fiber optic distributed temperature sensing. Free convection that can occur in the pipe of the heat exchanger was evaluated using the Rayleigh number stability criterion. The finite and infinite line source equations were used to reproduce temperature variations along the heating cable sections and continuous heating cable, respectively. The thermal conductivity profile of each site was inferred and the uncertainly of the test was evaluated. A mean thermal conductivity 15% higher than that revealed with the conventional test was estimated with heating cable sections. The thermal conductivity evaluated using the continuous heating cable corresponds to the value estimated during the conventional test. The average uncertainly associated with the heating cable section test was 15.18%, while an uncertainty of 2.14% was estimated for the test with the continuous heating cable. According to the Rayleigh number stability criterion, significant free convection can occur during the heat injection period when heating cable sections are used. The continuous heating cable with a low power source is a promising method to perform thermal response tests and further tests could be carried out in deep boreholes to verify its applicability.

Energy harvesting devices for subsea sensors

Subsea engineering has become a thriving field that received a lot of attention from researchers and educators in recent years. The reason for the attention could be economical since many oil and gas fields are offshores, ecological due to pollution, or geological due to earthquakes and Tsunamis. The subsea environment is difficult to conquer and requires sophisticated tools to monitor such as Autonomous or Remote Underwater Vehicles (AUVs or ROVs), submersible sensors, and very skilled manpower. In this work, the focus is on how to supply power indefinitely to stationary sensors at the bottom of the sea. Therefore, an energy harvesting device is designed and simulated to validate its efficacy in supplying the necessary power to charge submersible sensors and their accessories. The device is actuated using water currents and the output voltage is fed through a voltage rectifier to convert it to the required DC input of the sensors. Simulations results showed that the designed device can successfully provide the necessary power for submersible sensors.

Low-Cost Pneumatic Sensor for Water Level Detection in Gauging Stations

Permanent stream gauge stations are a vital feature of river monitoring and water management worldwide, and their use is rapidly increasing. Water level sensors in gauging stations are subjected to a harsh physical environment and are generally the most troublesome component and may easily introduce corrosion, electrical interference and other potentially damaging influences to the other components. One technology currently available to address the shortcomings of traditional submersible sensors is pneumatic detection of stage. The primary advantage of this type of sensor is that it provides physical separation of electrical components from the water. They are also highly advantageous in systems with high silt or debris loads. The cost of pneumatic sensors has fallen in recent years and is comparable with submersible pressure sensors of similar range and resolution. The issue with pneumatic sensors is that there is a large gap in the literature addressing the development, use and accuracy of this sensor type. This paper presents a case study detailing the development and use of a low-cost pneumatic sensor and examines its suitability for use in streams and irrigation canals. The performance of the sensor is also evaluated against two types of traditional low-cost submersible pressure sensors. Copyright © 2015 John Wiley & Sons, Ltd.

Retention time generates short-term phytoplankton blooms in a shallow microtidal subtropical estuary

In this study it was hypothesised that increasing water retention time promotes phytoplankton blooms in the shallow microtidal Patos Lagoon estuary (PLE). This hypothesis was tested using salinity variation as a proxy of water retention time and chlorophyll a for phytoplankton biomass. Submersible sensors fixed at 5 m depth near the mouth of PLE continuously measured water temperature, salinity and pigments fluorescence (calibrated to chlorophyll a) between March 2010 and 12th of December 2011, with some gaps. Salinity variations were used to separate alternating patterns of outflow of lagoon water (salinity <8; 46% of the time) and inflow of marine water (salinity >24; 35% of the time). The two transition phases represented a rapid change from lagoon water outflow to marine water inflow and a more gradually declining salinity between the dominating inflow and outflow conditions. During the latter of these, a significant chlorophyll a increase relative to that expected from a linear mixing relationship was observed at intermediate salinities (10–20). The increase in chlorophyll a was positively related to the duration of the prior coastal water inflow in the PLE. Moreover, chlorophyll a increase was significantly higher during austral spring-summer than autumn-winter, probably due to higher light and nutrient availability in the former. Moreover, the retention time process operating on time scales of days influences the long-term phytoplankton variability in this ecosystem. Comparing these results with monthly data from a nearby long-term water quality monitoring station (1993–2011) support the hypothesis that chlorophyll a accumulations occur after marine inflow events, whereas phytoplankton does not accumulate during high water outflow, when the water residence time is short. These results suggest that changing hydrological pattern is the most important mechanism underlying phytoplankton blooms in the PLE.

Automated Detections of Carcinogenic Compounds in Estuaries: A Short Review

Cancer accounted around 13% of all deaths in 2008. About 70% of all cancer deaths occurred in low and middle income countries. Deaths from cancer worldwide are projected to continue to rise to over 13.1 million in 2030. Previous reports indicated that reservoir such as rivers and lakes contain various carcinogenic compounds. The carcinogens are being transported from the release points to the intake points. To avoid this phenomenon happen, the fast and accurate detection of carcinogens concentrations in water is crucial. This review presents automated detection methods of carcinogenic compounds in watercourses. Automated detections, particularly the application of sensors, have a relatively higher speed and sensitivity compared to chemical and biological approaches. However, sensors application limits on its functions. This review gives a description on the history of automated detections and various types of sensors such as automated optical sensor, submersible ultraviolet fluorometer sensor, photoelectrochemical sensor with the detection of DNA damage and trihalomethanes (THMs) sensor for detection of carcinogenic compounds. Sensors are varied according to specific types of carcinogens.

Piezoelectric Resonant Sensors with Contactless Interrogation for Mass-Sensitive and Acoustic-Load Detection

Abstract Piezoelectric resonator sensors that can be contactless interrogated as passive elements are proposed. The interrogation technique is based on time-gated excitation and detection phases, exploiting the sensing of the transient response of the resonator. The proposed system can be exploited for the measurement of physical or chemical quantities affecting the electromechanical resonant response. In particular, experimental results show the successful interrogation of variable-mass resonator sensors for humidity sensing in closed volumes and submersible resonator sensors operated in liquid environments.

A mobile monitoring system to understand the processes controlling episodic events in Corpus Christi Bay

Corpus Christi Bay (TX, USA) is a shallow wind-driven bay and thereby, can be characterized as a highly pulsed system. It cycles through various episodic events such as hypoxia, water column stratification, sediment resuspension, flooding, etc. Understanding of the processes that control these events requires an efficient observation system that can measure various hydrodynamic and water quality parameters at the multitude of spatial and temporal scales of interest. As part of our effort to implement an efficient observation system for Corpus Christi Bay, a mobile monitoring system was developed that can acquire and visualize data measured by various submersible sensors on an undulating tow-body deployed behind a research vessel. Along with this system, we have installed a downward-looking Acoustic Doppler Current Profiler to measure the vertical profile of water currents. Real-time display of each measured parameter intensity (measured value relative to a pre-set peak value) guides in selecting the transect route to capture the event of interest. In addition, large synchronized datasets measured by this system provide an opportunity to understand the processes that control various episodic events in the bay. To illustrate the capability of this system, datasets from two research cruises are presented in this paper that help to clarify processes inducing an inverse estuary condition at the mouth of the ship channel and hypoxia at the bottom of the bay. These measured datasets can also be used to drive numerical models to understand various environmental phenomena that control the water quality of the bay.

In situ determination of organic compounds in liquid samples using a combined UV-Vis/fluorescence submersible sensor

In order to improve the in situ evaluation and quantitative analysis of complex contaminations of liquid media such as ground-, surface, and wastewaters, an integrated submersible sensor probe has been developed. It is especially characterized by the option of simultaneously measuring ultraviolet/visible (UV/Vis) and fluorescence spectra. Owing to the compact construction with light sources, flow cell, detection system, and data acquisition/processing unit in the waterproof case, the data transfer to the surface can be realized electrically, and the operation depth is practically not limited. The variability in the measuring techniques allows a wide variety of chemical compounds to be analysed within a broad concentration range. The performance of the new submersible sensor probe was tested ex situ in laboratory scale, and the performance was comparable with that of stationary measuring instruments. As an example for an in situ application, the sensor probe was successfully used to monitor the migration of chemical substances during a tracer experiment in groundwater. The concentration of the tracer compound uranin (sodium fluorescein) was measured in the range of 5–500 µg L−1 using fluorescence spectroscopy, while at the same time the contents of toluene were continuously detected in the same groundwater wells using the UV/Vis sensor channel.

Submarine lidar for seafloor inspection

Substances released at sea by accident or illegal discharges are characterized by a broad range of chemical and physical properties. Moreover, the characteristics of coastal waters, e.g. in the German Bight, are highly variable. Due to this a submersible sensor network for the detection of hazardous substances on the seafloor combining several instruments based on different physical and chemical principles has been under development since 1996. In addition to conventional sensors for seawater analysis and seafloor monitoring such as CTD probes (conductivity, temperature, depth) and video cameras, the system includes several newly developed instruments for the detection of dissolved and sunken pollutants. One of these instruments is the submarine lidar, combining a range-gated imaging device and a fluorescence lidar. A q-switched Nd:YAG laser is used as the common light source. Applying the expanded frequency-doubled laser pulse the gated CCD camera is particularly useful for recording images of damaged containers with chemical cargo where harmful substances might be released into the water column. Tuned to UV emission, the same laser is used for remotely classifying fluorescent substances spreading on the seafloor. The intention of this paper is to present the submarine lidar in detail and to give an overview of its physics and potential applications.

A submersible flow injection-based sensor for the determination of total oxidised nitrogen in coastal waters

The design and construction of a remotely deployed submersible sensor for the determination of total oxidised nitrogen (nitrate plus nitrite) in seawater is described. It was based on the flow injection principle with solid state spectrophotometric detection of the diazotisation product from the reaction of nitrite with N-(1-naphthyl)ethylenediamine dihydrochloride (N1NED) and sulphanilamide. Nitrate was pre-reduced in-line with a copperised cadmium powder column. The limit of detection (3 s) was 0.1 μM nitrate (1.4 μg l −1 N) and the linear range was 0.1–55 μM nitrate with a 20 mm path length flow cell and a 260 μl sample loop. The linear range was modified for different environmental conditions by changing the sample loop size and - or the flow cell path length. Results are presented for preliminary laboratory studies and field trials in the Tamar Estuary and for deployments in the North Sea. The sensor was successfully deployed on three separate occasions for complete tidal cycles (13 h) at a depth of 4 m from the bow of RRS Challenger. Field data are compared with results from a shipboard air segmented analyser and correlated with turbidity and salinity data.

Diagnostics of the stages and development of boiling of sodium inside fuel assemblies according to neutron flux noise

Part of the sodium flowing into the boiling generator was passed through tungsten rods assembled into a bundle, similar to the bundle of fuel elements in a fuel assembly. The other part of the sodium flowed over a gas-filled cladding surrounding the heating zone. This made it possible to prevent unnecessary leakage of heat out of the boiling zone. In the experiments on BN-350, the boiling generator was installed, instead of a KP-6 compensation packet, at a radial distance of 260 mm from the center of the core. The working part of the generator in the initial state was placed below the core in the region of the bottom screen. Heat release in the heating zone was regulated by inserting the working part into the core. The position of the boiling generator was monitored with the aid of a selsyn placed on the actuating mechanism of the KP-6 compensation mechanism. The boiling process was monitored according to signals from submersible (with a lithium niobate sensitive element) and waveguide acoustic sensors as well as standard ionization chambers placed above the core. The assemblies with the sensors were installed inside the thermocouple chambers and the receptacle for the backup refueling mechanism. Standard KNK-56 ionization chambers were placed in the thermal column 5100 mm from the center of the core. Two series of experiments were performed on the BN:350 reactor. The first series was performed in the period when the reactor reached power in order to check the working capacity of the boiling generator and to adjust the measuring channels of the monitoring apparatus. The first indications of boiling were recorded as a change in the characteristics of the neutron noise at 480 MW with the working part of the boiling generator completely inserted into the core. At powers of 560 MW and higher, boiling was also recorded according to the acoustic signals. After the reactor reached the working power level of 700 MW, two experiments were performed. In the first experiment, boiling was maintained for 12 min and in the second experiment boiling was maintained for 35 min.