All data shown here are read directly from the IMOS EMII data portal into Matlab using opendap protocols, at the time shown on the graphic.
ADCP - Acoustic Doppler Current Profiler. The ANMN have used several types: the RDI Workhorse, RDI Continental and Nortek AWAC units, all deployed as upward-looking units, either rigidly on the bottom, or in taut moorings.
U, V - Current velocity components along orthogonal axes. These estimates are at a number of equi-spaced vertical distances from the ADCP, i.e. the manufacturer's software has taken the tilt of the unit into account. For moorings that do not undergo large vertical displacement, these data can be used directly to estimate velocity at a range of depth levels. This is what we do here. For ADCPs that change their depth a lot, users will probably want to re-grid the velocity data from range coordinates to range+depth(t) coordinates.
ABSI - Acoustic Back-Scatter Intensity, without correction for the average range-dependent attenuation.
ADCP-T - Temperature at the depth of the ADCP.
ADCP-P - Pressure at the depth of the ADCP. This is a measure of both the mooring motion and the tidal elevation, and is shown to help trouble-shoot apparently spurious estimates of U and V. In some files this is a constant. Note that some instruments may suffer drift of the pressure data.
ADCP-D - Depth of the ADCP. For some files this is missing, so we use ADCP-P, or the 'nominal depth' in the global attributes.
ADCP-tilt - A combination of the ADCP Pitch and Roll data, which are in the ADCP instrumental coordinate system.
SurfaceBinKnockdown - This is a diagnostic calculation of the approximate depth anomaly of the nominal surface bin resulting from the instrument tilt, also shown just for trouble-shooting purposes.
Surface blanking interval - ADCP velocity estimates are contaminated by side-lobe interference with the surface for a significant distance beneath the surface. The thickness of this affected layer is about 12% of the nominal instrument depth but also depends on the instrument acoustic characteristics (frequency, beam width, etc), the tilt and the sea state.
For an introductory discussion of some highlights of the data, see our 27 March 2013 and 2 July 2013 News Items.
- 11 June 2014 update: We have now completed a refresh of all our plots of the ANMN velocity data that is presently available at the IMOS portal. What's new:
As earlier, there are multi-instrument (e.g. at right) and multi-depth-layer map views as well as the calendar-style index page.
- an additional year or so of data,
- ADCP data from the NRS moorings,
- clarification of whether compass data has been corrected for magnetic declination,
- minor improvements to information shown on plots, and choice of U and V axes.
- removal of some erroneous datasets.
- August 2013 Update: It appears that few or no ADCP datasets have been rotated to True East and North, so the files on the EMII portal (and our plots) all need to be corrected. The correction is negligible in WA, and small in SA, so this mainly affects NSW where magnetic north is 15T. The location with the greatest inter-deployment variability of the mean current and LF motion is off Elusive Reef (SGBR) in the path of the East Australian Current. QC of this data is also being checked.
- 23 July 2013 update. Includes two new sets of map views: multi-instrument (e.g. at right) and multi-depth-layer, both showing the i) mean current speed and direction (for each deployment interval), and ii) principal component analysis of the sub-tidal variability. One motive for these analyses is to check for evidence of compass errors. The clearest example of this is for the CH100 Dec 2012 - Jan 2013 data which is clearly misaligned. For many instruments there is also the possibility that correction for magnetic declination has not been made, so the data are with respect to magnetic east and north rather than the intended true east and north. This is being investigated by the ANMN facility.
- 1 July 2013 update. As below, but after a re-scan of the ANMN ADCP data archive at EMII
- ADCP U, V, ABSI, ADCP-T, ADCP-P/D, SurfaceBinKnockdown, 2007-2013 using the most error-tolerant QC flags. U,V and ABSI data are used whenever the corresponding QC flag is not 4 (='bad'). The index pages give an overview of the data availability, 3 years per page, east, south and west sectors of Australia separately. The (single) quantity plotted on these index pages is the magnitude of the depth-averaged current velocity (i.e. not the depth-average of the current speed) at 2h resolution, just as a preview of the nature of the data. Click the graphic to see page-per-deployment plots of variables listed. The amount of 'cleaning' achieved by this level of QC, at the time of writing (26 Mar 2013), is quite variable, i.e. good for some files but very incomplete for others. In order to filter out the spurious velocities (which are quite obvious in some of the time-depth plots), we show a dotted white line at 12-14% of the nominal instrument depth (see the zc listed at top right), and omit this surface layer from the depth-average current shown on the index pages. The plots show (at top right) the toolbox version used (2.1b). When the files have been re-processed using toolbox version 2.2 we will updata these plots.
- As above, but ignoring QC flags This shows the U,V,ABSI without any filtering by QC flag, for a selection of files in the east and west sectors.
- As above, but with stringent QC on the U,V data This shows the U,V data filtered by requiring the QC flag to be 1 ('good'), for a selection of files in the east and west sectors.
For further information
IMOS Australian National Moorings Network (ANMN) Facility
AIMS site CSIRO NRS site
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