scholarly journals The Finescale Response of Lowered ADCP Velocity Measurements Processed with Different Methods

2012 ◽  
Vol 29 (4) ◽  
pp. 597-600 ◽  
Author(s):  
A. M. Thurnherr
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Processing Method ◽  
Vertical Shear ◽  
Inversion Method ◽  
Velocity Data ◽  
Velocity Measurements ◽  
Processing Methods ◽  
Velocity Inversion ◽  
Current Profiler ◽  
Specific Implementation

Abstract In a paper published in 2002 in this journal, K. Polzin et al. derive corrections for spectra of vertical shear calculated from lowered acoustic Doppler current profiler (LADCP) velocity data. To illustrate and validate the corrections, they use velocities derived with a specific implementation of the shear method for LADCP processing that is no longer supported or widely used. In several recent publications, spectral corrections specific to this old processing method have been applied without modification to LADCP data processed with the more modern and much more widely used velocity-inversion method, which is associated with significantly less damping at high vertical wavenumbers than the older method. The purpose of this work is to derive and validate spectral corrections appropriate for different LADCP processing methods.

scholarly journals Using Orthogonal Combined Signals in Broadband ADCP for Improving Velocity Measurement

2020 ◽  
Vol 8 (6) ◽  
pp. 450
Author(s):  
Yujing Lin ◽  
Fei Yuan ◽  
En Cheng
Keyword(s):  
Current Velocity ◽  
Velocity Measurement ◽  
Water Environment ◽  
Acoustic Doppler Current Profiler ◽  
Processing Method ◽  
Velocity Measurements ◽  
Signal Parameters ◽  
Current Profiler ◽  
Signal Combination ◽  
Conventional Signal

Broadband Acoustic Doppler Current Profiler (BBADCP) is a widely used technology in velocity measurements. To adapt to the varied water environment and different measurement requirements, flexible tuning of transmitted signal parameters will improve the feasibility and accuracy of velocity measurement. Compared with the conventional signal, the orthogonal combined signal designed in this paper can generate a wealth of signal combination examples and improve the accuracy of the velocity measurement under the same conditions. The proposed orthogonal combined signal consists of two orthogonal sub-signals with a symmetrical spectrum. Each is designed based on time delay to eliminate or weaken the current velocity ambiguity. Then, the processing method of the received signal when the pulse signals are the same or different coded signal is discussed. The numerical simulation results show that, when using the proposed method, the standard deviation of the estimated current velocity has different degrees of reduction at different current velocities. Our simulation also shows that, compared to the convention method, the proposed method can improve the SNR by 10 dB. This can help significantly increase the scope of the configuration.

Variability of the Horizontal Velocity Structure in the Upper 1600 m of the Water Column on the Equator at 10°W

2006 ◽  
Vol 36 (7) ◽  
pp. 1287-1304 ◽  
Author(s):  
Lucia Bunge ◽  
Christine Provost ◽  
Jonathan M. Lilly ◽  
Marc D’Orgeville ◽  
Annie Kartavtseff ◽  
...  
Keyword(s):  
Water Column ◽  
Velocity Component ◽  
Velocity Structure ◽  
Strong Dependence ◽  
Acoustic Doppler Current Profiler ◽  
Horizontal Velocity ◽  
Vertical Shear ◽  
Equatorial Atlantic ◽  
Entire Water Column ◽  
Current Profiler

Abstract This paper presents initial results from new velocity observations in the eastern part of the equatorial Atlantic Ocean from a moored current-meter array. During the “EQUALANT” program (1999–2000), a mooring array was deployed around the equator near 10°W that recorded one year of measurements at various depths. Horizontal velocities were obtained in the upper 60 m from an upward-looking acoustic Doppler current profiler (ADCP) and at 13 deeper levels from current meters between 745 and 1525 m. To analyze the quasiperiodic variability observed in these records, a wavelet-based technique was used. Quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands: 5–10, 10–20, 20–40, and 40–100 days. The variability shows (i) a strong seasonality (the first half of the series is dominated by larger periods than the second one) and (ii) a strong dependence with depth (some oscillations are present in the entire water column while others are only present at certain depths). For the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface, while for the others the question of their origin remains open. Phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales. This is especially visible in long-duration events (>100 days) of the zonal velocity component. Comparison with a simultaneous lowered acoustic Doppler current profiler (LADCP) section suggests that some of these flows may be identified with equatorial deep jets. A striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m. These deep current-meter observations would then imply a few months of duration for the jets in this region.

scholarly journals Analysis of in situ water velocity distributions in the lowland river floodplain covered by grassland and reed marsh habitats - a case study of the bypass channel of Warta River (Western Poland)

2017 ◽  
Vol 65 (4) ◽  
pp. 325-332 ◽  
Author(s):  
Ireneusz Laks ◽  
Krzysztof Szoszkiewicz ◽  
Tomasz Kałuża
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Water Velocity ◽  
Concrete Slabs ◽  
Lowland River ◽  
Vegetation Types ◽  
Velocity Measurements ◽  
Flow Energy ◽  
Current Profiler

AbstractThe analysis of in situ measurements of velocity distribution in the floodplain of the lowland river has been carried out. The survey area was located on a bypass channel of the Warta River (West of Poland) which is filled with water only in case of flood waves. The floodplain is covered by grassland and reed marsh habitats. The velocity measurements were performed with an acoustic Doppler current profiler (ADCP) in a cross-section with a bed reinforced with concrete slabs. The measured velocities have reflected the differentiated impact of various vegetation types on the loss of water flow energy. The statistical analyses have proven a relationship between the local velocities and the type of plant communities.

scholarly journals Identifikasi Arus Pasang Surut di Perairan Kemujan, Karimunjawa Berdasarkan Data Pengukuran Acoustic Doppler Current Profiler

2021 ◽  
Vol 24 (2) ◽  
pp. 247-254
Author(s):  
Elis Indrayanti ◽  
Denny Nugroho Sugianto ◽  
Purwanto Purwanto ◽  
Hendry Syahputra Ropinus Siagian
Keyword(s):  
Tidal Current ◽  
Acoustic Doppler Current Profiler ◽  
Tidal Currents ◽  
Residual Current ◽  
Least Square ◽  
Ocean Currents ◽  
Velocity Data ◽  
Raw Data ◽  
Current Profiler ◽  
X 24

Ocean currents are dynamic hydro-oceanographic parameters which is play an important role in the transport of nutrients, larvae, sediment, and so on. Therefore, the identification of ocean currents including velocity, direction, sea level and the type of currents important to be studied. The research was conducted in Kemujan Water, Karimunjawa. Data for this research is based on velocity data measured using the Acoustic Doppler Current Profiler (ADCP) for 3 x 24 hours. Furthermore, the raw data of the measurement are analyzed using least square methods to obtain the characteristic of tidal current. The total current is separated into tidal currents and residual current (non-tidal currents). Result shown that the characteristic of current in Kemujan Water, Karimunjawa was tidal current. Tidal current moves bi-directional, toward the northeast and the southwest.. Arus laut merupakan parameter hidro-oseanografi yang dinamis dan mempunyai peran penting dalam transpor nutrien, larva, material, dan lain sebagainya. Oleh karena itu identifikasi arus laut meliputi kecepatan, arah, elevasi muka air laut dan tipe arus laut perlu untuk dikaji. Penelitian dilaksanakan di Perairan Kemujan  yang merupakan salah satu gugusan pulau di Karimunjawa. Data  yang dianalisa merupakan data kecepatan arus hasil pengukuran langsung menggunakan Acoustic Doppler Current Profiler (ADCP) selama 3x24 jam. Selanjutnya raw data hasil pengukuran diolah dengan metode least square untuk mengetahui karakteristik arus. Arus total dipisahkan menjadi arus pasang surut dan arus non-pasang surut (residu). Hasil penelitian menunjukkan bahwa prosentase arus pasang surut lebih besar dari arus residu, sehingga arus di Perairan Kemujan, Karimunjawa teridentifikasi sebagai arus pasang surut. Arus  bergerak secara bertolak belakang (bi-directional) yaitu pada saat surut menuju pasang arah arus menuju ke timur laut dan pada saat pasang menuju surut arah arus menuju ke barat daya.

scholarly journals Method for processing XCP data with improved accuracy

2017 ◽  
Vol 6 (1) ◽  
pp. 209-215
Author(s):  
Xinyue Zhang ◽  
Qisheng Zhang ◽  
Xiao Zhao ◽  
Qimao Zhang ◽  
Shenghui Liu ◽  
...  
Keyword(s):  
Electric Field ◽  
Data Processing ◽  
Acoustic Doppler Current Profiler ◽  
Accurate Method ◽  
Current Data ◽  
Processing Method ◽  
Ocean Current ◽  
Data Processing Method ◽  
Current Profiler ◽  
Improved Accuracy

Abstract. An expendable current profiler (XCP) is a device used for monitoring ocean currents. In this study, we focus on the technology available for processing XCP data and propose a more accurate method for calculating the current velocity from the nanovolt-scale current-induced electric field measured using an XCP. In order to confirm the accuracy of the proposed data processing method, a sea test was performed in the South China Sea region, wherein, for the first time in China, ocean current and electric-field data were collected from the sea surface to a depth of 1000 m using an XCP. The current-data processing method described herein was used to determine the eastward and northward relative velocity components of the current from the measured data, which were then compared with the current data obtained using an acoustic Doppler current profiler, in order verify the accuracy of the measurements as well as that of the data processing method.

scholarly journals Analysis of acoustic Doppler current profiler mean velocity measurements in shallow flows

2020 ◽  
Vol 74 ◽  
pp. 101755
Author(s):  
Matthew R. Klema ◽  
Abdul G. Pirzado ◽  
S. Karan Venayagamoorthy ◽  
Timothy K. Gates
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Shallow Flows ◽  
Current Profiler

scholarly journals A Practical Assessment of the Errors Associated with Full-Depth LADCP Profiles Obtained Using Teledyne RDI Workhorse Acoustic Doppler Current Profilers

2010 ◽  
Vol 27 (7) ◽  
pp. 1215-1227 ◽  
Author(s):  
A. M. Thurnherr
Keyword(s):  
Linear Equations ◽  
Sampling Rate ◽  
Velocity Profiles ◽  
Processing Method ◽  
Velocity Shear ◽  
Inversion Method ◽  
Velocity Inversion ◽  
Single Constraint ◽  
Uncertainty Estimates ◽  
Acoustic Doppler Current Profilers

Abstract Lowered acoustic Doppler current profilers (LADCPs) are commonly used to measure full-depth velocity profiles in the ocean. Because LADCPs are lowered on hydrographic wires, elaborate data processing is required to remove the effects of instrument motion from the velocity measurements and to transform the resulting relative velocity profiles into a nonmoving reference frame. Two fundamentally different methods are used for this purpose: in the velocity inversion method, a set of linear equations is solved to separate the ocean and instrument velocities while simultaneously applying a combination of velocity-referencing constraints from navigational data, shipboard ADCP measurements, and bottom tracking. In the shear method, a gridded profile of velocity shear, which is not affected by instrument motion, is vertically integrated and referenced using a single constraint. The main goals of the present study consist in estimating the accuracy of LADCP-derived velocity profiles and determining which processing method performs better. To this purpose, 21 LADCP profiles collected during four surveys are compared to velocities measured simultaneously by nearby moored instruments at depths between 2000 and 3000 m. The LADCP data were processed with two slightly different publicly available implementations of the velocity inversion method, as well as with an implementation of the shear method that was extended to support multiple simultaneous velocity-referencing constraints. Regardless of the processing method, the overall rms LADCP velocity errors are <3 cm s−1 as long as multiple velocity-referencing constraints are imposed simultaneously. On the other hand, solutions referenced with a single constraint are associated with significantly greater errors. The two primary instrument characteristics that influence data quality are range and sampling rate. Dependence of the LADCP velocity errors on those two parameters was determined by reprocessing range-limited subsets and temporal subsamples of the LADCP data. Results indicate an approximately linear increase of the velocity errors with decreasing sampling rate. The relationship between velocity errors and instrument range is much less linear and characterized by a steep increase in velocity errors below a limiting range of ≈60 m. To improve the quality of the velocity data by increasing the instrument range, modern LADCP systems often include both upward- and downward-looking ADCPs. The data analyzed here indicate that the addition of a second ADCP can be as effective as doubling the range of a single-head LADCP system. However, in one of the datasets the errors associated with the profiles calculated from combined up- and down-looker data are significantly larger than the corresponding errors associated with the profiles calculated from the down-looker alone. The analyses carried out here indicate that the velocity errors associated with LADCP profiles can be significantly smaller than expected from previously published results and from the uncertainty estimates calculated by the velocity inversion method.

scholarly journals The Development of an Inversion Technique to Extract Vertical Current Profiles from X-Band Radar Observations

2016 ◽  
Vol 33 (9) ◽  
pp. 2015-2028 ◽  
Author(s):  
Jeffrey Campana ◽  
Eric J. Terrill ◽  
Tony de Paolo
Keyword(s):  
Doppler Shift ◽  
Acoustic Doppler Current Profiler ◽  
Wave Dispersion ◽  
Ocean Waves ◽  
Vertical Shear ◽  
Inversion Method ◽  
Radar Backscatter ◽  
Forward Solution ◽  
Test Environment ◽  
X Band

AbstractThe influence of wave–current interactions on time series of marine X-band radar backscatter maps at the mouth of the Columbia River (MCR) near Astoria, Oregon, is examined. The energetic wave environment at the MCR, coupled with the strong tidally forced currents, provides a unique test environment to explore the limitations in accurately determining the magnitude and vertical structure of upper-ocean currents from wavefield measurements. Direct observation in time and space of the wave-induced radar backscatter and supporting acoustic Doppler current profiler (ADCP) current measurements provide a rich dataset for investigating how currents shift the observed wave dispersion relationship. First, current extraction techniques that assume a specific current–depth profile are tested against ADCP measurements. These constrained solutions prove to have inaccuracies because the models do not properly account for vertical shear. A forward solution using measured current profiles to predict the wavenumber–Doppler shift relationship for the range of ocean waves sensed by the radar is introduced. This approach confirms the ocean wavefield is affected by underlying vertical current shear. Finally, a new inversion method is developed to extract current profiles from the wavenumber-dependent Doppler shift observations. The success of the inversion model is shown to be sensitive to the range of wavenumbers spanned by observed Doppler shifts, with skill exceeding 0.8 when wavenumbers span more than 0.1 rad m−1. This agreement when observations successfully capture the broadband wavefield suggests the X-band backscatter is a viable means of remotely estimating current shear.

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