Journal articles: 'Towed sensor'

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Curtis, C. S. "Towed underwater acoustic speed sensor." Journal of the Acoustical Society of America 96, no. 3 (September 1994): 1942. http://dx.doi.org/10.1121/1.410216.

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Dugan, J. P., and B. W. Stalcup. "Comparison of Towed Conductivity Sensor Performance." Journal of Atmospheric and Oceanic Technology 5, no. 1 (February 1988): 116–22. http://dx.doi.org/10.1175/1520-0426(1988)005<0116:cotcsp>2.0.co;2.

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Fraser, Douglas C., and Greg Hodges. "Induction-response functions for frequency-domain electromagnetic mapping system for airborne and ground configurations." GEOPHYSICS 72, no. 2 (March 2007): F35—F44. http://dx.doi.org/10.1190/1.2405845.

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A helicopter-towed electromagnetic (EM) sensor of the type typically flown in frequency-domain surveys may be towed over the ground on a trailer. The in-phase and quadrature components measured by a trailer-towed sensor will be dramatically different from those determined when the sensor is flown. For the airborne case, the in-phase and quadrature curves of the induction-response function are governed by the superposed-dipole behavior, in which flying height substantially exceeds the transmitting-receiving coil separation. In contrast, for a ground-based sensor, the coil separation substantially exceeds the sensor height, yielding the infinitely separated dipole case in which the sensor height is negligible compared to the coil separation. These two end cases — the superposed dipole and the infinitely separated dipole —yield EM amplitudes and phase angles that are very different from each other. For the superposed-dipole case of the airborne sensor, the in-phase component reaches a high positive value as the EM response approaches the inductive limit, whereas for the infinitely separated dipole case of the ground sensor, the in-phase component reaches a large negative value. Consequently, there must be a sensor height where the in-phase becomes zero at the inductive limit. This critical height is approximately 35% of the coil separation for the maximum coupled horizontal coplanar coils of the helicopter-towed EM system. The resolution of the ground sensor is superior to that of the airborne sensor, whereas the depth of exploration for the airborne sensor is superior to that of the ground sensor. This finding is to be expected from a consideration of the size of the footprint of the sensor.

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Jahan, Kausar, and Koteswara Rao Sanagapallea. "Fusion of Angle Measurements from Hull Mounted and Towed Array Sensors." Information 11, no. 9 (September 9, 2020): 432. http://dx.doi.org/10.3390/info11090432.

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Two sensor arrays, hull-mounted array, and towed array sensors are considered for bearings-only tracking. An algorithm is designed to combine the information obtained as bearing (angle) measurements from both sensor arrays to give a better solution. Using data from two different sensor arrays reduces the problem of observability and the observer need not follow the S-maneuver to attain observability of the process. The performance of the fusion algorithm is comparable to that of theoretical Cramer–Rao lower bound and with that of the algorithm when bearing measurements from a single sensor array are considered. Different filters are used for analyzing both algorithms. Monte Carlo runs need to be done to evaluate the performance of algorithms more accurately. Also, the performance of the fusion algorithm is evaluated in terms of solution convergence time.

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Orji, Okwudili, Walter Söllner, and Leiv Jacob Gelius. "Imaging the sea surface using a dual-sensor towed streamer." GEOPHYSICS 75, no. 6 (November 2010): V111—V118. http://dx.doi.org/10.1190/1.3496439.

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Sea-surface profile and reflection coefficient estimates are vital input parameters to various seismic data processing applications. The common assumption of a flat sea surface when processing seismic data can lead to misinterpretations and mislocations of events. A new method of imaging the sea surface from decomposed wavefields has been developed. Wavefield separation is applied to the data acquired by a towed dual-sensor streamer containing collocated pressure and vertical particle velocity sensors to obtain upgoing and downgoing wavefields of the related sensors. Time-gated upgoing and downgoing wavefields corresponding to a given sensor are then extrapolated to the sea surface where an imaging condition is applied so that the time-invariant shape of the sea surface can be recovered. By sliding the data time-window, the temporal changes of the sea surface can be correspondingly estimated. Ray tracing and finite-difference methods were used to generate different controlled data sets used in this feasibility study to demonstrate the imaging principle and to test the image accuracy. The method was also tested on a first field data example of a marginal weather line from the North Sea.

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Barr, Frederick J. "Noise reference sensor for use in a dual sensor towed streamer." Journal of the Acoustical Society of America 114, no. 1 (2003): 23. http://dx.doi.org/10.1121/1.1601052.

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Day, Anthony, Tilman Klüver, Walter Söllner, Hocine Tabti, and David Carlson. "Wavefield-separation methods for dual-sensor towed-streamer data." GEOPHYSICS 78, no. 2 (March 1, 2013): WA55—WA70. http://dx.doi.org/10.1190/geo2012-0302.1.

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A dual-sensor towed streamer records the pressure and vertical component of particle motion associated with the incident wavefield that may be used to separate the wavefield into its up- and downgoing parts. This procedure requires information about the water properties (wave-propagation velocity and density) and is robust in the presence of errors in the estimation of these quantities of the magnitude likely to be encountered. In practice, the particle motion data recorded by current towed marine streamers encounter very strong mechanical noise such that, for the lowest frequencies, the wavefield separation must be approximated by deconvolving the ghost function from the pressure data. This procedure requires information about the streamer depth and is robust to small depth errors over the frequency range for which it is required for dual-sensor streamer processing, but it is much more sensitive if applied over the bandwidth necessary to deghost pressure data acquired at a conventional streamer depth. The signal-to-noise ratio can be further enhanced by recombining the up- and downgoing pressure fields at the sea surface, which has the effect of applying a ghostlike filter to noise that is recorded by only one of the two sensors. In practical marine acquisition scenarios, spatial sampling is often insufficient to yield an accurate result, especially in the crossline direction. If each streamer is processed independently assuming that the wavefield propagation is purely inline, significant errors can be introduced. For arrivals with high emergent angles, errors may also be introduced even if the wavefield propagation actually is purely inline due to incorrect treatment of spatially aliased energy. However, these effects are almost entirely confined to very shallow events. They can be mitigated by using independently derived information about the crossline propagation angle and, for data comprising predominantly forward scattered energy, appropriate application of linear moveout.

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Korte, Holger. "Track Control of a Towed Underwater Sensor Carrier." IFAC Proceedings Volumes 33, no. 9 (June 2000): 89–94. http://dx.doi.org/10.1016/s1474-6670(17)38129-6.

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Capps, Rodger N. "Exploratory materials development for towed array sensor systems." Journal of the Acoustical Society of America 94, no. 3 (September 1993): 1840. http://dx.doi.org/10.1121/1.407751.

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Lampert, Astrid, Jörg Hartmann, Falk Pätzold, Lennart Lobitz, Peter Hecker, Katrin Kohnert, Eric Larmanou, Andrei Serafimovich, and Torsten Sachs. "Comparison of Lyman-alpha and LI-COR infrared hygrometers for airborne measurement of turbulent fluctuations of water vapour." Atmospheric Measurement Techniques 11, no. 4 (May 2, 2018): 2523–36. http://dx.doi.org/10.5194/amt-11-2523-2018.

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Abstract. To investigate if the LI-COR humidity sensor can be used as a replacement of the Lyman-alpha sensor for airborne applications, the measurement data of the Lyman-alpha and several LI-COR sensors are analysed in direct intercomparison flights on different airborne platforms. One vibration isolated closed-path and two non-isolated open-path LI-COR sensors were installed on a Dornier 128 twin engine turbo-prop aircraft. The closed-path sensor provided absolute values and fluctuations of the water vapour mixing ratio in good agreement with the Lyman-alpha. The signals of the two open-path sensors showed considerable high-frequency noise, and the absolute value of the mixing ratio was observed to drift with time in this vibrational environment. On the helicopter-towed sensor system Helipod, with very low vibration levels, the open-path LI-COR sensor agreed very well with the Lyman-alpha sensor over the entire frequency range up to 3 Hz. The results show that the LI-COR sensors are well suited for airborne measurements of humidity fluctuations, provided that a vibrationless environment is given, and this turns out to be more important than close sensor spacing.

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Won, I. J., Alex Oren, and Frank Funak. "GEM‐2A: A programmable broadband helicopter‐towed electromagnetic sensor." GEOPHYSICS 68, no. 6 (November 2003): 1888–95. http://dx.doi.org/10.1190/1.1635041.

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We present a new helicopter‐towed broadband electromagnetic sensor, GEM‐2A, for mineral prospecting and geologic mapping. The sensor uses one set of transmitter and receiver coils for a multifrequency operation. For a given survey, the user initially specifies a set of operational frequencies in the current bandwidth of 90 Hz to 48 kHz. The transmitter coil then emanates a current waveform that contains all specified frequencies. The duration of this current waveform, called the base period, is typically 1/30 s (a submultiple of local powerline frequency) resulting in an overall data rate at 30 Hz. Receiver channels digitize the secondary field into a time series over a base period, which is then subjected to discrete sine and cosine transforms or convolutions at each transmitted frequency to produce the raw in‐phase and quadrature data. Additional convolutions may be included for passively monitoring environmental noise, including powerline emissions. The entire operation, including the system upload/download and realtime monitoring and communication, is done in Microsoft Windows. The fact that the sensor contains only a single set of coils for the broadband operation provides several unique advantages, some of which include (1) co‐relatable and coherent drift characteristics among frequencies, (2) spectral integrity among frequencies that may be useful for anomaly classification and, possibly, mineral discrimination, (3) tolerance to sferics, (4) tolerance to powerline noise, and (5) light tow body with minimal cockpit hardware suitable for a small helicopter. This paper presents the sensor construction, operation, and data examples.

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Thode, Aaron, Jeff Skinner, Pam Scott, Jeremy Roswell, Janice Straley, and Kendall Folkert. "Tracking sperm whales with a towed acoustic vector sensor." Journal of the Acoustical Society of America 128, no. 5 (November 2010): 2681–94. http://dx.doi.org/10.1121/1.3495945.

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Joseph V., Jojish, Unnikrishnan N, and Sooraj K. Ambat. "Fault Detection and Prognostic Health monitoring of Towed array sonars." Defence Science Journal 72, no. 3 (July 1, 2022): 495–503. http://dx.doi.org/10.14429/dsj.72.17377.

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Sonars are used to detect underwater targets and are especially important in maintaining naval superiority. Towed array sonars can operate at very low frequencies thus giving larger ranges and can be deployed to any desired depth of operation. Towed array sonars offer long range surveillance capability and is the sensor of choice for sustained surveillance operations. Reliable operation and maintenance of towed array sonars need effective methods of health monitoring and reliability prediction. For any prognostic health monitoring to be done we need to identify certain parameters which can be observed and will give system health status in the present condition. This paper proposes some metrics which are easily measurable in-situ and which offer insights into the health of the sonar system. These metrics give direct measureable impact for each of the failure modes and offer insights into the current health of an operational towed array sonar. Simulation results are shown to demonstrate the effectiveness of the proposed metrics and detailed trial data results from different towed array trials are analysed to validate them in operational scenarios.

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Orji, Okwudili C., Walter Söllner, and Leiv-J. Gelius. "Imaging 3D Sea Surfaces from 3D Dual-Sensor Towed Streamer Data." International Journal of Geophysics 2013 (2013): 1–13. http://dx.doi.org/10.1155/2013/387175.

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3D realistic sea surface imaging from 3D dual-sensor towed streamer data is presented. The technique is based on separating data acquired by collocated dual-sensors into up-going and down-going wavefields. Subsequently, these wavefields are extrapolated upwards in order to image the sea surface. This approach has previously been demonstrated using 2D data examples. Here, the focus is on 3D data. Controlled 3D data based on the Kirchhoff-Helmholtz algorithm is generated, and the 3D sea surface imaging technique is applied. For coarsely spaced streamers from 3D field data, the technique is applied streamerwise (i.e., 2D wavefield separation, extrapolation, and imaging). In the latter case, the resulting sea surface profiles corresponding to each time frame are interpolated to demonstrate that the main sea surface characteristics are preserved, and artefacts due to 2D processing of 3D data are mainly limited to areas corresponding to large angles of incidence. Time-varying sea surfaces from two different 3D field data are imaged. The data examples were acquired under different weather conditions. The imaged sea surfaces show realistic wave heights, and their spectra suggest plausible speeds and directions.

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Shin, Hyun-Kyoung, Jung-Soo Ryue, Hyung-Taek Ahn, Hee-Seon Seo, and Oh-Cho Kwon. "Study on dynamic behavior analysis of towed line array sensor." International Journal of Naval Architecture and Ocean Engineering 4, no. 1 (March 31, 2012): 9–19. http://dx.doi.org/10.3744/jnaoe.2012.4.1.009.

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Shin, Hyun Kyoung, Jung Soo Ryue, Hyung-Taek Ahn, Hee Seon Seo, and Oh-Cho Kwon. "Study on dynamic behavior analysis of towed line array sensor." International Journal of Naval Architecture and Ocean Engineering 4, no. 1 (March 2012): 9–19. http://dx.doi.org/10.2478/ijnaoe-2013-0074.

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Billings, Stephen, and Laurens Beran. "Optimizing electromagnetic sensors for unexploded ordnance detection." GEOPHYSICS 82, no. 3 (May 1, 2017): EN25—EN31. http://dx.doi.org/10.1190/geo2016-0232.1.

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Time-domain electromagnetic (TEM) instruments are the predominant geophysical sensor for detection of buried unexploded ordnance (UXO). Detection surveys commonly use towed TEM sensor arrays to acquire a digital map for target detection. We use a dipolar model to predict a detection threshold for a UXO at a specified clearance depth, given an arbitrary sensor geometry. In general, the minimum target response is obtained for a horizontally oriented target. We find that for multistatic sensors, the minimum response can also depend on the azimuth of the target. By considering the statistics of the target response, we find that the detection threshold can be raised slightly while still ensuring a high probability of detection of UXO at depth. This increase in the detection threshold can have a significant effect on the number of false alarms that need to be interrogated or investigated and hence on the cost of clearance. We also use Monte Carlo simulation to investigate how array geometry and height affect clutter rejection.

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Moh, Taejun, Namdo Jang, Seok Jang, and Jin Hyung Cho. "Application of a Winch-type Towed Acoustic Sensor to a Wave-powered Unmanned Surface Vehicle." Defence Science Journal 67, no. 1 (December 23, 2016): 125. http://dx.doi.org/10.14429/dsj.67.10577.

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Although many countries have focused on anti-submarine warfare for several decades, underwater submarines can hardly be detected by current assets such as patrol aircraft, surface ships and fixed underwater surveillance systems. Due to the difficult conditions of the oceanic environment and the relative quietness of submarines, existing acoustic surveillance platforms are not able to fully cover their mission areas. To fill in the gaps, a winch-type towed acoustic sensor system was developed and integrated into a wave-powered unmanned surface vehicle by the Korea Institute of Ocean Science and Technology. In June 2015, sea trial tests were conducted to verify maneuvering, acoustic signal detection, and communication capabilities. During the maneuvering test, the wave-powered glider successfully moved along programmed waypoints. Despite towing the acoustic sensor system, only 20% of initial electricity was consumed in 20 days. The acoustic sensor was lowered to depths of 100–150 m by the winch system, and received signals from an acoustic simulator lowered to depths of 50–100 m by RV Jangmok. Simulated submarine noises that were refracted downward could be clearly received and classified by the hydrophone system, from distances of 2–8 km, while it was being towed silently and deeply. In addition, an optical camera provided high-resolution images of surface vessels, allowing integration with acoustic detection of underwater objects. In conclusion, this new platform using a deeply towed hydrophone system is worthy of consideration as an underwater surveillance asset. Future work is required to strengthen inter-asset communication and obstacle avoidance, and to overcome strong currents to make this technology a reliable part of the underwater surveillance network.

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Nakamura, Masahiko, Tadahiro Hyakudome, Takafumi Kasaya, Hisanori Iwamoto, and Yutaka Ohta. "Motion simulation of sensor cable towed by X rudder AUV “YUMEIRUKA"." Journal of the Japan Society of Naval Architects and Ocean Engineers 29 (2019): 89–102. http://dx.doi.org/10.2534/jjasnaoe.29.89.

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Whitmore, N. D., A. A. Valenciano, W. Söllner, and S. Lu. "Imaging of primaries and multiples using a dual-sensor towed streamer." ASEG Extended Abstracts 2010, no. 1 (December 2010): 1–2. http://dx.doi.org/10.1081/22020586.2010.12042051.

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Huang, Haoping, Bill SanFilipo, Alex Oren, and I. J. Won. "Coaxial coil towed EMI sensor array for UXO detection and characterization." Journal of Applied Geophysics 61, no. 3-4 (March 2007): 217–26. http://dx.doi.org/10.1016/j.jappgeo.2006.06.005.

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Pharez, Stephen, Natasha Hendrick, and Rune Tenghamn. "First look at seismic data from a towed dual-sensor streamer." Leading Edge 27, no. 7 (July 2008): 904–7. http://dx.doi.org/10.1190/1.2954031.

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Korenbaum, Vladimir, and Alexander Tagiltsev. "Flow noise of underwater vector sensor embedded in a flexible towed array." Journal of the Acoustical Society of America 129, no. 4 (April 2011): 2516. http://dx.doi.org/10.1121/1.3588319.

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Kim, Geun Hwan, Su Jin Choi, Chang Soo Ryu, Young Woo Ryu, and Kyun Kyung Lee. "Towed Array Shape Estimation based on Kalman Filter Compensating the Sensor Bias." Journal of the Korea Institute of Military Science and Technology 19, no. 2 (April 5, 2016): 155–62. http://dx.doi.org/10.9766/kimst.2016.19.2.155.

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Cho, Yohan, Yub Je, and Weui-Bong Jeong. "A miniaturized acoustic vector sensor with PIN-PMN-PT single crystal cantilever beam accelerometers." Acta Acustica 4, no. 5 (2020): 17. http://dx.doi.org/10.1051/aacus/2020017.

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Directional sound detection using vector sensors rather than large hydrophone arrays is highly advantageous for target detection in SONAR. However, developing highly sensitive and compact vector sensors for use in a system whose size is limited has been a challenging issue. In this paper, we describe a miniaturized acoustic vector sensor with piezoelectric single crystal accelerometers for the application in towed line arrays. A mass-loaded cantilever beam accelerometer with a [011] poled PIN-PMN-PT single crystal shows a better signal-to-noise ratio compared to accelerometers with other piezoelectric materials because of its superior piezoelectric properties in the 32 direction. We suggested a sufficiently compact vector sensor by using a cylindrical hydrophone with 10 mm in diameter as a housing of the single crystal accelerometers. Two single crystal accelerometers were orthogonally mounted inside the cylindrical hydrophone to detect direction of sound in the transverse plane of the line array. The receiving voltage sensitivity of the accelerometers and hydrophone was −199 and −196 dB, respectively, at 3 kHz. The directional cardioid beams generated by summing the omnidirectional beam from the hydrophone and the dipole beam from the accelerometers were validated over the entire operating frequency.

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Lapucci, Tommaso, Luigi Troiano, Carlo Carobbi, and Lorenzo Capineri. "Soft and Hard Iron Compensation for the Compasses of an Operational Towed Hydrophone Array without Sensor Motion by a Helmholtz Coil." Sensors 21, no. 23 (December 3, 2021): 8104. http://dx.doi.org/10.3390/s21238104.

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Usually, towed hydrophone arrays are instrumented with a set of compasses. Data from these sensors are utilized while beamforming the acoustic signal for target bearing estimation. However, elements of the hydrophone array mounted in the neighborhood of a compass can affect the Earth’s magnetic field detection. The effects depend upon the materials and magnetic environment present in the vicinity of the platform hosting the compass. If the disturbances are constant in time, they can be compensated for by means of a magnetic calibration procedure. This process is commonly known as soft and hard iron compensation. In this paper, a solution is presented for carrying out the magnetic calibration of a COTS (Commercial Off the Shelf) digital compass without sensor motion. This approach is particularly suited in applications where a physical rotation of the platform that hosts the sensor is unfeasible. In our case, the platform consists in an assembled and operational towed hydrophone array. A standard calibration process relies on physical rotation of the platform and thus on the use of the geomagnetic field as a reference during the compensation. As a variation on this approach, we generate an artificial reference magnetic field to simulate the impractical physical rotation. We obtain this by using a tri-axial Helmholtz coil, which enables programmability of the reference magnetic field and assures the required field uniformity. In our work, the simulated geomagnetic field is characterized in terms of its uncertainty. The analysis indicates that our method and experimental set-up represent a suitably accurate approach for the soft and hard iron compensation of the compasses equipped in the hydrophone array under test.

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Korenbaum, Vladimir I., and Alexander A. Tagiltsev. "Flow noise of an underwater vector sensor embedded in a flexible towed array." Journal of the Acoustical Society of America 131, no. 5 (May 2012): 3755–62. http://dx.doi.org/10.1121/1.3693647.

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Pytka, Jaroslaw, Piotr Budzyński, Tomasz Łyszczyk, Jerzy Józwik, Joanna Michałowska, Arkadiusz Tofil, Dariusz Błażejczak, and Jan Laskowski. "Determining Wheel Forces and Moments on Aircraft Landing Gear with a Dynamometer Sensor." Sensors 20, no. 1 (December 31, 2019): 227. http://dx.doi.org/10.3390/s20010227.

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This paper describes airfield measurement of forces and moments that act on a landing gear wheel. For the measurement, a wheel force sensor was used. The sensor was designed and built based on strain gage technology and was embedded in the left landing gear wheel of a test aircraft. The sensor is capable of measuring simultaneously three perpendicular forces and three moments and sends data to a handheld device wirelessly. For the airfield tests, the sensor was installed on a PZL 104 Wilga 35A multipurpose aircraft. The aircraft was towed at a “marching man” speed and the measurements were performed at three driving modes: Free rolling, braking, and turning. The paper contains results obtained in the field measurements performed on a grassy runway of the Rzeszów Jasionka Aerodrome, Poland. Rolling resistance of aircraft tire, braking friction, as well as aligning moment were analyzed and discussed with respect to surface conditions.

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Zumberge, Mark A., Jeff R. Ridgway, and John A. Hildebrand. "A towed marine gravity meter for near‐bottom surveys." GEOPHYSICS 62, no. 5 (September 1997): 1386–93. http://dx.doi.org/10.1190/1.1444243.

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Gravity is measured presently on the sea surface and on the sea floor. Surface gravity suffers from loss of resolution over the deep ocean because the perturbing source masses are far from the observer. Bottom measurements recover this resolution, but suffer from poor coverage because of the time needed for each measurement. We have constructed a gravimetry system that combines the rapid data collection capability of a moving platform with the high resolution gained by locating the observations near the bottom. This gravity sensor is tethered to a ship and towed just above the sea floor. The instrument consists of a LaCoste and Romberg shipboard gravity meter modified to fit inside a pressure case that is mounted on a platform designed for towing stability. We have tested it in a survey in the San Diego Trough, a 1000-m—deep sedimented valley in the Pacific Ocean in the California continental borderlands. Multiple gravity tracklines collected there at a depth of 935 m show a resolution of a few tenths of a mGal. The new instrument will be useful for surveys of features whose lateral extent is equal to or less than the ocean depth.

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Thode, Aaron M., Jeff Skinner, Pam Scott, Jeremy Roswell, Janice Straley, and Kendall Folkert. "Tracking sperm whales with a towed acoustic vector sensor using physics‐based noise analysis." Journal of the Acoustical Society of America 128, no. 4 (October 2010): 2462. http://dx.doi.org/10.1121/1.3508820.

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Popper, Arthur N., Michele B. Halvorsen, Diane Miller, Michael E. Smith, Jiakun Song, Lidia E. Wysocki, Mardi C. Hastings, Andrew S. Kane, and Peter Stein. "Effects of surveillance towed array sensor system (SURTASS) low frequency active sonar on fish." Journal of the Acoustical Society of America 117, no. 4 (April 2005): 2440. http://dx.doi.org/10.1121/1.4809471.

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Govind, V. Kiran, S. O. Santosh Kumar, T. S. Sinoj, K. R. Thulasidas, and M. Sabu Sebastian. "Design and Development of Depth Activated Inflatable Recovery System for Undersea Towed Sensor Arrays." Aquatic Procedia 4 (2015): 449–57. http://dx.doi.org/10.1016/j.aqpro.2015.02.096.

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Kolster, Mick Emil, and Arne Døssing. "Scalar magnetic difference inversion applied to UAV-based UXO detection." Geophysical Journal International 224, no. 1 (October 8, 2020): 468–86. http://dx.doi.org/10.1093/gji/ggaa483.

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SUMMARY During scalar magnetic surveys, where the amplitude of the magnetic field is measured, small changes in towed sensor positions can produce complex noise-resembling signals in the data. For well-constructed measurement systems, these signals often contain valuable information, rather than noise, but it can difficult to realize their potential. We present a simple, general approach, which can be used to directly invert data from scalar magnetic surveys, regardless of dynamic or unexpected sensor position variations. The approach generalizes classic along-track gradients to an iterative, or recursive, difference, that can be applied irrespective of the amount of magnetic sensors and their positions within a dynamic measurement system, as long as these are known. The computed difference can be inverted directly, providing a versatile method with very little data pre-processing requirements, which we denote as recursive difference inversion. We explain the approach in a general setting, and expand it to provide a complete framework for Unexploded Ordnance (UXO) detection using a point-dipole model. Being an extension of classic along-track gradients, the method retains many of the same properties, which include added robustness to external time-dependent disturbances, and the ability to produce aesthetic visual data representations. In addition, the framework requires neither tie lines, data levelling, nor diurnal corrections. Only light pre-processing actions, namely initial survey trimming and data position calculation, are required. The method is demonstrated on data from a dual sensor system, conventionally referred to as a vertical gradiometer, which is towed from an Unmanned Aerial Vehicle. The system enables collection of high-quality magnetic data in adverse settings, and simultaneously reduces the risk of inadvertent UXO detonations. To enable qualitative testing, we established a UXO detection test facility with several buried UXO, typical to World War II, in a magnetically complex in-land area. Data from the test facility was mainly used to evaluate inversion robustness and depth accuracy of the point-dipole model. Subsequently, we apply the method to real UXO survey data collected for the Hornsea II offshore wind farm project in the United Kingdom. This data set was collected in a coastal setting, and subject to significant sensor position changes during flight due to varying wind conditions over multiple survey days. This makes the raw data set challenging to interpret directly, but it can still be easily and reliably inverted for source locations through recursive difference inversion. In each of the two data sets, we attempt to recover UXO positions using recursive difference inversion on data from both a single sensor, as well as on data from two synchronized sensors, in each case inverting the difference directly for point-dipole model parameters. To seed the inversion, we propose a simple routine for picking out potential targets, based on the choice of a significant peak prominence in the time-series of computed differences. Higher order difference inversion was found to provide robust results in the magnetically complex setting, and the recovered equivalent dipole depths were found to approximate the actual UXO depths well.

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Ridgway, Jeff R., and Mark A. Zumberge. "Deep‐towed gravity surveys in the southern California Continental Borderland." GEOPHYSICS 67, no. 3 (May 2002): 777–87. http://dx.doi.org/10.1190/1.1484521.

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We surveyed two sites in the southern California continental borderland with a newly developed instrument, a towed deep ocean gravimeter—a gravity sensor that can be towed a few tens of meters above the sea floor. During its development phase, we used the instrument to survey two regions off the coast of southern California. The first was along two tracks in the San Diego Trough. The second was over a seamount‐like feature named Emery Knoll. Results of the trough survey reveal a basin with a geometry consistent with seismic data. We observed no significant density contrast across the San Diego Trough fault in the near‐surface sediments. The survey of Emery Knoll shed light on the question of the origin of this structure; modeling the knoll to determine its bulk density suggested a nearly uniform structure surrounded by sedimentary basins with a more massive central intrusive body. Derived densities of 2850 kg/m3 for the knoll and 3050 kg/m3 for the central intrusion assume that no deep unmodeled sources exist directly underneath the knoll. The gravity data favor a model of metamorphic basement rock uplifted and containing igneous intrusives.

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Kass, M. Andy, Esben Auken, Jakob Juul Larsen, and Anders Vest Christiansen. "A towed magnetic gradiometer array for rapid, detailed imaging of utility, geological, and archaeological targets." Geoscientific Instrumentation, Methods and Data Systems 10, no. 2 (November 29, 2021): 313–23. http://dx.doi.org/10.5194/gi-10-313-2021.

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Abstract. Efficient and accurate acquisition of magnetic field and gradient data have applications over a large range of environmental, archaeological, engineering, and geologic investigations. Developments in new systems and improvements in existing platforms have progressed to the point where magnetic surveying is a heavily used and trusted technique. However, there is still ample room to improve accuracy and coverage efficiency and to include reliable vector information. We have developed a vector magnetic gradiometer array capable of recording high-resolution field and gradient data over tens of hectares per day at 50 cm sensor spacing. Towed by an all-terrain vehicle, the system consists of eight vertical gradiometer sensor packages and incorporates differential GPS and an inertial measurement system. With a noise floor of around 6 nT at 15 km/h towing speed and 230 Hz sample rates, large areas can be mapped efficiently and precisely. Data are processed using a straightforward workflow, using both standard and newly developed methodologies. The system described here has been used successfully in Denmark to efficiently map buried structures and objects. We give two examples from such applications highlighting the system's capabilities in archaeological and geological applications.

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Wang, Lijie, Shuang Zhang, Shudong Chen, and Chaopeng Luo. "Underground Target Localization Based on Improved Magnetic Gradient Tensor With Towed Transient Electromagnetic Sensor Array." IEEE Access 10 (2022): 25025–33. http://dx.doi.org/10.1109/access.2022.3156080.

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Filonov, A. E. "On the interpretation of short-period fluctuations in the thermocline obtained from a towed sensor." Ciencias Marinas 23, no. 2 (April 1, 1997): 209–25. http://dx.doi.org/10.7773/cm.v23i2.794.

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FUJIMURA, Ryo, Atsushi KAKOGAWA, and Shugen MA. "Pipeline Mapping using a Towed Unit Equipped with a Wheel Encoder and a Gyro Sensor." Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) 2021 (2021): 2P3—I14. http://dx.doi.org/10.1299/jsmermd.2021.2p3-i14.

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Meng, Zhou, Wei Chen, Jianfei Wang, Xiaoyang Hu, Mo Chen, and Yichi Zhang. "Recent Progress in Fiber-Optic Hydrophones." Photonic Sensors 11, no. 1 (January 22, 2021): 109–22. http://dx.doi.org/10.1007/s13320-021-0618-5.

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AbstractFiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.

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Díaz Charris, Vladimir, and Juan A. Contreras Montes. "Design and development of route planner for Unmanned Surface Vehicles." Ciencia y tecnología de buques 11, no. 21 (September 15, 2017): 89. http://dx.doi.org/10.25043/19098642.151.

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This paper describes the development of a route planner for Unmanned Surface Vehicles (USVs) focused on the study of an operational scenario for a specific mission – Anti-Submarine Warfare (ASW). Through the design and implementation of a simulation model, the effect of the different factors that particularly influence ASW is analyzed, such as search pattern, speed and sensor type; dipping sonar or towed array sonar (TAS). By obtaining a measurement of effectiveness, the USV’s response in the deployment of this type of mission can be defined using time to detect the threat in a search area, as parameters to measure the performance.

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Pidcock, Rosalind, Meric Srokosz, John Allen, Mark Hartman, Stuart Painter, Matt Mowlem, David Hydes, and Adrian Martin. "A Novel Integration of an Ultraviolet Nitrate Sensor On Board a Towed Vehicle for Mapping Open-Ocean Submesoscale Nitrate Variability." Journal of Atmospheric and Oceanic Technology 27, no. 8 (August 1, 2010): 1410–16. http://dx.doi.org/10.1175/2010jtecho780.1.

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Abstract Initial results from a deployment of the SUV-6 ultraviolet spectrophotometer, integrated with the SeaSoar towed vehicle, are presented. The innovative, combined system measures nitrate concentration at high spatial resolution (4 m vertically, 5 km horizontally), high sensitivity (0.2 μM), and concomitantly with temperature, salinity, and dissolved oxygen. The authors demonstrate that this approach constitutes a powerful new tool for quantifying the role of mesoscale and submesoscale vertical nutrient fluxes to the euphotic zone, using measurements from a high-resolution survey of an eddy dipole in the Iceland Basin during the summer of 2007.

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Finger, Fanny, Frank Werner, Marcus Klingebiel, André Ehrlich, Evelyn Jäkel, Matthias Voigt, Stephan Borrmann, Peter Spichtinger, and Manfred Wendisch. "Spectral optical layer properties of cirrus from collocated airborne measurements and simulations." Atmospheric Chemistry and Physics 16, no. 12 (June 23, 2016): 7681–93. http://dx.doi.org/10.5194/acp-16-7681-2016.

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Abstract. Spectral upward and downward solar irradiances from vertically collocated measurements above and below a cirrus layer are used to derive cirrus optical layer properties such as spectral transmissivity, absorptivity, reflectivity, and cloud top albedo. The radiation measurements are complemented by in situ cirrus crystal size distribution measurements and radiative transfer simulations based on the microphysical data. The close collocation of the radiative and microphysical measurements, above, beneath, and inside the cirrus, is accomplished by using a research aircraft (Learjet 35A) in tandem with the towed sensor platform AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected from two field campaigns over the North Sea and the Baltic Sea in spring and late summer 2013. One measurement flight over the North Sea proved to be exemplary, and as such the results are used to illustrate the benefits of collocated sampling. The radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius reff, and optical thickness τ on cirrus spectral optical layer properties. Furthermore, the radiative effects of low-level, liquid water (warm) clouds as frequently observed beneath the cirrus are evaluated. They may cause changes in the radiative forcing of the cirrus by a factor of 2. When low-level clouds below the cirrus are not taken into account, the radiative cooling effect (caused by reflection of solar radiation) due to the cirrus in the solar (shortwave) spectral range is significantly overestimated.

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Kolster, Mick Emil, Mark David Wigh, Eduardo Lima Simões da Silva, Tobias Bjerg Vilhelmsen, and Arne Døssing. "High-Speed Magnetic Surveying for Unexploded Ordnance Using UAV Systems." Remote Sensing 14, no. 5 (February 25, 2022): 1134. http://dx.doi.org/10.3390/rs14051134.

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Using Uncrewed Aerial vehicles (UAVs) to rapidly scan areas for potential unexploded ordnance (UXO) can provide an efficiency increase while minimizing detonation risks. We present a complete overview of how such mappings can be performed using scalar magnetometers, including initial sensor testing, time stamping validation, data positioning, noise removal, and source model inversion. A test survey was performed across disarmed UXO targets, during which three scalar magnetometers were towed in an airframe (“bird”) 10 m below a small (<25 kg) high speed (∼10 m/s) UAV to avoid magnetic disturbances from the UAV itself. Data were collected across ∼58 min of flight, with each sensor traversing ∼31.7 km to acquire dense data coverage across a 600 m × 100 m area. By using three individual magnetometers in the bird, UXO detection results across single-sensor data and several different multi-sensor configurations can be compared. The data obtained exhibited low apparent noise floors (on the order of tens of picoTesla) and retained a precision that enabled targeted modelling and removal of high-frequency noise with amplitudes of ±5 picoTesla. All of the different gradiometer configurations tested enabled recovery of most targets (including all major targets), although the horizontal configuration performed significantly worse in comparison.

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Lee, James B., David L. Dart, Robert J. Turner, Mark A. Downey, Arthur Maddever, Goran Panjkovic, Catherine P. Foley, et al. "Airborne TEM surveying with a SQUID magnetometer sensor." GEOPHYSICS 67, no. 2 (March 2002): 468–77. http://dx.doi.org/10.1190/1.1468606.

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Traditionally airborne time-domain electromagnetic (AEM) survey systems use induction coils as the sensor (receiver). We have replaced the induction coil in a transient electromagnetic (TEM) system with a liquid-nitrogen cooled superconducting quantum interference device (SQUID) magnetometer sensor. Using this prototype system, we aimed to improve performance in detecting conductive mineralization, particularly where the conductive mineralization of interest is covered by a conductive regolith. We successfully demonstrated one- and three-component SQUID sensors in airborne TEM surveying, and achieved performance comparable to the induction-coil systems. Implementation of the SQUID system required development of devices capable of operating in magnetically unshielded environments with low noise, high slew rate, and wide bandwidth. Operation of the SQUID sensor in the highly dynamic environment of a towed bird was also necessary, and this implies a high dynamic range and high level of noise associated with the motion in Earth's magnetic field. The high dynamic range of the SQUID response was handled by a combination of resetting the SQUID flux locked loop, reducing the bandwidth, and providing high-gain feedback in parallel with the flux locked loop. A digital stacking filter was used to eliminate low-frequency noise associated with sensor motion. Isolation of the sensor from motion at the TEM signal frequencies required development of a sophisticated suspension system. The SQUID systems were tested over two known conductive targets, and their performance compared with the induction-coil TEM system. A comparative performance measure is developed to take the different sensitivities of the SQUID magnetometer and induction-coil receivers into account. This measure indicates that the SQUID system has superior performance for responses over earth structures with decay time constants greater than ∼6 ms when compared with the induction-coil signals. We also estimate the performance in comparison with integrated outputs of the induction-coil system and show that, at the demonstrated levels of SQUID performance, it is expected to have poorer performance by a factor of two or more. This disadvantage will be reduced for lower frequency, wider channel width TEM configurations or by improvements in the SQUID devices.

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Rudd, Jonathan, Glenn Chubak, Hugo Larnier, Ronny Stolz, Markus Schiffler, Vyatcheslav Zakosarenko, Michael Schneider, Marco Schulz, and Matthias Meyer. "Commercial operation of a SQUID-based airborne magnetic gradiometer." Leading Edge 41, no. 7 (July 2022): 486–92. http://dx.doi.org/10.1190/tle41070486.1.

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Gradient measurement of the magnetic field vector, especially full-tensor magnetic gradiometers (FTMGs), provides various advantages over gradient components derived from measurements of the total magnetic intensity (TMI). These advantages include higher spatial resolution, directional information, and thus more detailed anomaly delineation and a significantly better-constrained solution space for magnetic inversion and interpretation. However, the airborne application of FTMG instruments requires exceptionally high sensor resolution and low levels of motion noise to maximize these advantages and to achieve high exploration depth. Superconducting quantum interference detectors (SQUIDs) are an effective option for FTMG sensors, now available commercially in the system discussed herein. This SQUID sensor system comprises intrinsic planar-type gradiometers that produce data with sufficiently low noise for use on an airborne platform. The evolution and advancement of the system and its predecessor over the past two decades has produced a robust commercial system that produces high-quality full-tensor data sets from a helicopter-towed-bird implementation. Because the SQUID sensors measure directionally sensitive data, the processing of the acquired data is significantly more challenging than for TMI sensors. Noise induced by the motion of the bird during flight, especially rotational noise, must be monitored and compensated. The introduction of a more robust and aerodynamic bird has significantly reduced the noise of the system. This noise reduction translates into greater sensitivity and accuracy and, thus, heightened confidence in the use of the survey data sets. While much of the early use of the system has been in diamondiferous kimberlite exploration, the system has successfully flown surveys in mineral exploration for a variety of targets, including gold, nickel, and iron ore. These data sets provide greater confidence in the geologic interpretation across the survey areas. Other applications for FTMG surveying include infrastructure mapping, unexploded ordnance detection, and compensation of electromagnetic data sets in marine environments.

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Schmidt, Mark, Peter Linke, Stefan Sommer, Daniel Esser, and Sergiy Cherednichenko. "Natural CO2 Seeps Offshore Panarea: A Test Site for Subsea CO2 Leak Detection Technology." Marine Technology Society Journal 49, no. 1 (January 1, 2015): 19–30. http://dx.doi.org/10.4031/mtsj.49.1.3.

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AbstractDuring RV Poseidon cruise POS469 (May 2014), the distribution of pCO2 in the near field of submarine volcanic gas flares in shallow water depths down to 50 m below sea level was continuously monitored using three different and independent methodologies. In situ nondispersive infrared (NDIR) spectrometry, pH measurements, and onboard membrane inlet mass spectrometry (MIMS) were used to determine the fate of rising CO2 bubbles and the dissolved CO2 plume patterns in a 300 × 400-m working area. The In situ sensor carrier platform, a towed video-controlled water sampling rosette, equipped with CTD sensors, guaranteed excellent ground truthing of seafloor characteristics and bubble discharge. Sensor data and near-seafloor observations indicated that the gas bubbles (<9 mm in diameter, >97 vol.% of CO2) dissolved very rapidly within the first 10 m above seafloor. Bottom water masses enriched with pCO2 (up to 1,100 μatm) show low pH values (up to 7.80) and tend to spread rather downslope west than following the measured weak current in SSE-SSW direction. The 3-D evaluation of pCO2 plume is a valuable tool to back-trace the origin of CO2 leakage when compared with local current regimes, water column CTD data, and seafloor bathymetry. Seep sites offshore Panarea can be used for studying CO2 leakage behavior and testing measuring strategies in shallow waters. Moreover, this area is a naturally designed laboratory to improve existing physicochemical and oceanographic transport models for subsea CO2 leakage.

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Kusuma, Hollanda Arief, Indra Jaya, and Henry Munandar Manik. "DESIGN AND IMPLEMENTATION OF ELECTRONIC LOGGING INSTRUMENT TO HELP SCIENTIFIC DIVER IN CORAL REEF MONITORING." Marine Research in Indonesia 41, no. 1 (July 15, 2016): 37–49. http://dx.doi.org/10.14203/mri.v41i1.96.

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Indonesia is situated in the Coral Triangle region that has the world’s highest coral reef biodiversity. Therefore, coral reef monitoring needs to be conducted regularly to assess the condition of coral reef ecosystem for management purpose. There are several coral reef monitoring methods available such as the line intercept transect (LIT), point intercept transect (PIT), photo transect, belt transect and benthic towed-diver. In Indonesia, LIT and PIT are the most commonly used methods for coral monitoring. However, there is a main disadvantage when collecting data using these methods, that is scientific divers need to spend hours to input the data after dives. Here, we introduce an electronic logging instrument called Coral Input Data Instrument that helps to decrease the input data time by employing a look-up table system that simplifies data input process by replacing text with numerical coding. In addition, water quality data such as temperature, depth and visibility also are embedded in the electronic logging instrument. The instrument hardware consists of Arduino Mega 2560, keypad 4x3, LCD Module 16x2 character, real time clock, temperature sensor, pressure sensor, visibility sensor and micro SD card module. Arduino IDE 1.6.5 software is used to program the microcontroller. In this paper, we describe the design and implementation of the instrument in the field.

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Wolk, Fabian, Hidekatsu Yamazaki, Hua Li, and Rolf G. Lueck. "Calibrating the Spatial Response of Bio-Optical Sensors." Journal of Atmospheric and Oceanic Technology 23, no. 3 (March 1, 2006): 511–16. http://dx.doi.org/10.1175/jtech1863.1.

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Abstract This article describes an experimental method used to establish the spatial wavenumber response of in situ fluorometers. The method is applied to a fluorometer developed to measure the structure of the fluorescence field at high spatial wavenumbers. This fluorometer detects fluorescence variations on centimeter scales by creating a sampling volume in the undisturbed flow region, outside of the sensor housing. The sampling volume is created by intersecting beams of blue excitation light. To establish the size of the sampling volume and the amount of spatial averaging, the fluorometer and a fast response thermistor are towed repeatedly through a warm, fluorescent plume in a tow tank. The ratio of the measured fluorescence and temperature spectrum determines the wavenumber response of the fluorometer. The measured spectral ratio is well described by the transfer function of a first-order, low-pass filter with a half-power point at 22 cpm. The equivalent spatial resolution is 7 mm. The transfer function model can be used to correct measured fluorescence spectra for the limited wavenumber response of the sensor.

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Yoerger, Dana R., Annette F. Govindarajan, Jonathan C. Howland, Joel K. Llopiz, Peter H. Wiebe, Molly Curran, Justin Fujii, et al. "A hybrid underwater robot for multidisciplinary investigation of the ocean twilight zone." Science Robotics 6, no. 55 (June 16, 2021): eabe1901. http://dx.doi.org/10.1126/scirobotics.abe1901.

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Mesobot, an autonomous underwater vehicle, addresses specific unmet needs for observing and sampling a variety of phenomena in the ocean’s midwaters. The midwater hosts a vast biomass, has a role in regulating climate, and may soon be exploited commercially, yet our scientific understanding of it is incomplete. Mesobot has the ability to survey and track slow-moving animals and to correlate the animals’ movements with critical environmental measurements. Mesobot will complement existing oceanographic assets such as towed, remotely operated, and autonomous vehicles; shipboard acoustic sensors; and net tows. Its potential to perform behavioral studies unobtrusively over long periods with substantial autonomy provides a capability that is not presently available to midwater researchers. The 250-kilogram marine robot can be teleoperated through a lightweight fiber optic tether and can also operate untethered with full autonomy while minimizing environmental disturbance. We present recent results illustrating the vehicle’s ability to automatically track free-swimming hydromedusae (Solmissus sp.) and larvaceans (Bathochordaeus stygius) at depths of 200 meters in Monterey Bay, USA. In addition to these tracking missions, the vehicle can execute preprogrammed missions collecting image and sensor data while also carrying substantial auxiliary payloads such as cameras, sonars, and samplers.

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Johnson, R. F., and J. W. Rish. "Rolling Weight Deflectometer with Thermal and Vibrational Bending Compensation." Transportation Research Record: Journal of the Transportation Research Board 1540, no. 1 (January 1996): 77–82. http://dx.doi.org/10.1177/0361198196154000111.

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A pavement deflectometer has been developed for continuous measurement of airfield pavements under a rolling load wheel. The rolling weight deflectometer (RWD) measures pavement deflection using a new method of laser triangulation. It also compensates for bending of the beam on which the sensors are mounted. This compensation allows accurate measurement of deflection in the presence of motion and thermal effects. The deflection measurement incorporates data from four equally spaced pavement sensors mounted on a beam. The method requires the sensors to remain in a straight line at all times. This method was previously plagued with measurement errors caused by thermal and vibrational effects. The RWD uses a laser beam to monitor the state of bending of the physical beam in real time. The bending data are used with pavement sensor data to produce accurate deflection measurements in the presence of any amount of beam bending. The bending-compensated RWD produces deflection measurements on 0.3-m (1-ft) intervals with an accuracy of 40 microns (0.0015 in.) while moving at 10 km/hr (6 mph). The RWD is composed of a towed trailer, a networked data-acquisition system, and a load platform. Its essential elements consist of a horizontally transported beam, strategically placed pavement sensors, sensors to measure beam bending, an odometer, and a data-acquisition computer. A brief history of pavement deflection methods is presented along with a description of the RWD. Preliminary field results include a comparison between data obtained by a falling weight deflectometer and the RWD.

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Journal articles on the topic 'Towed sensor'

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