Page History

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ADCP Velocity Computation: Correction and Rotation to East-North-Up Co-ordinate System, Three-beam Solutions and Screening

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• range: vector of distance to each bin centre. If bin mapping compensation for tilt is active, this is then a vertical range to the bin centres, see adcp.processingComments to see if bin mapping was applied. To calculate the depth of each velocity bin, use the following:  

  if strcmp(Config.orient, 'Up')
    binDepth = Meta.depth - ADCP.range;
else
    binDepth = Meta.depth + ADCP.range;
end

• corr: 3D matrix, correlation time-series for each bin
• intens: 3D matrix, intensity time-series for each bin (also known as received signal strength intensity or RSSI, multiply by 0.45 dB/count to convert to a relative dB scale)
• velocity: 3D matrix, corresponds directly to output of instrument and so depends on configuration coordinate system
• percentGood: 3D matrix, percent good time-series for each bin
• ens: vector, ensemble number (replaced ensFirst for averaged products)
• ensFirst: vector of the first ensemble number in an ensemble average (averaged products only, replaces ens).
• compassHeading: vector, containing the EH values from the RDI files. This is either the fixed value from site and sitedevice headings (if not null), or values from an assigned true heading mobile position sensor. If neither, then it defaults to the magnetic compass heading data.
• pitch: vector, containing the EP values from the RDI files. This is either the fixed value from site and sitedevice headings (if not null), or values from an assigned true heading mobile position sensor. If neither, then it defaults to the onboard pitch sensor data.
• roll: vector, containing the ER values from the RDI files. This is either the fixed value from site and sitedevice headings (if not null), or values from an assigned true heading mobile position sensor. If neither, then it defaults to the onboard roll sensor data.
• time: vector, timestamp in datenum format (obtained from time the reading reached the shore station)
• temperature: vector, temperature time-series
• salinity: vector salinity time-series, (may contain constant values depending on device configuration)
• pressure: vector, pressure time-series. From RDI manual: "Contains the pressure of the water at the transducer head relative to one atmosphere (sea level). Output is in decapascals". Converted to decibar.
• depth: vector, depth of the device below the water surface as measured by the device for each ping. This will vary with the tide and more so if the device is mobile. It should be consistent with meta.depth. However, it may be in error. If any disagreement, take the value from meta.depthCan be set to a fixed value by the ED command / device attribute. For fixed deployments, this value is replaced in the RDI file by our code with the site depth plus offset, which is also reported as meta.depth. If not a fixed location deployment where the device is autonomous or mobile, this value is unaltered. It will vary with the tide and movement.
• soundSpeed: vector speed of sound time-series, (may contain constant values depending on device configuration)
• uMagnetic (optional): 2D matrix, East velocity relative to magnetic North
• vMagnetic (optional): 2D matrix, North velocity relative to magnetic North
• processingCommments: a string documenting all of the processing steps done to produce adcp.u/v/w. Use char(adcp.processingComments) to print out the text.
• processingOptions: a structure with the data product option set that was requested and what was actually done (not all options are available and maybe overriden at run time, this will be explained in the processingComments).
• velocity_sourceInfo: a string describing the source of data in adcp.velocity
• uvw_sourceInfo: a string describing the resulting final, rotated data in adcp.u/v/w
• u: 2D matrix, East velocity relative to True North
• v: 2D matrix, North velocity relative to True North
• w: 2D matrix, Upward Velocity
• u_std, v_std, w_std: standard deviations for ensemble averaged u,v,w (averaged products only)
• u_count, v_count, w_count: the number of ensembles/pings that contributed to u,v,w (averaged products only). Differs from pingsPerEnsemble in that it accounts for filtered / NaN-ed data
• velocityError: 2D matrix, computed using RDI algorithm
• backscatter: 3D matrix based on received signal strength intensity (adcp.intensity), compensated for two-way spreading (20LogR) and absorption. Equation based on Gostiaux and van Haren ("Extracting Meaningful Information from Uncalibrated Backscattered Echo Intensity Data, Journal of Atomsheric and Oceanic Technology, 72, 943-949, 2010). The absorption computation follows Ainslie and Malcolm ("A simplified formula for viscous and chemical absorption in sea water", Journal of the Acoustical Society of America, 103(3), 1671-1672, 1998). Absorption coefficient based on mean depth, temperature and salinity in adcp structure.
• meanBackscatter: same as above, except averaged over the four beams to create a 2D matrix. Averaging is done by converting to standard intensity, averaging, then converting back to decibels.

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