AODN releases new Velocity Aggregated Time Series product from IMOS moorings.
Measuring the currents in the ocean with moored instruments is a sophisticated process. Acoustic Doppler Current Profilers can measure the movement of the water at different heights above or below the sensor in three dimensions. The current meters can do the same but only at one particular depth. That results in a file with many variables used to calculate eastward (U), northward (V) and upward (W) velocity estimates. As usual, every deployment of an instrument represents one file in the AODN file system.
The velocity aggregated time series product, concatenates U, V, and W current values from all files corresponding to one site. It replaces the height above the sensor variable, which records the position of each measurement relative to the time-varying instrument depth, with the absolute depth at the time of measurement. To keep track of the provenance of the measurement, a variable called CELL_INDEX is included but it must not be used as a depth indicator. Now, the user only needs to access a single file in order to obtain all velocity measurements from one particular site. As in the previous aggregated product, only in-water measurements are stored and their quality control flags preserved. Expert users who wish to look at the data at its observed sampling frequency, without any interpolation through the water column, are the intended audience and encouraged to use this product.
The aggregated time series products (both velocity and other parameters) are available via the AODN THREDDS server, in a dedicated folder (“aggregated_timeseries”) inside each site folder. See here for example.
For help with reading the aggregated product files, see the examples in the aodn-user-code library (Python version, R version). Note that these examples access a different level of product, but the structure of the file is the same.
Detailed documentation of the product and the Python code used to produce the files is available at https://github.com/aodn/python-aodntools/tree/master/aodntools/timeseries_products. This GitHub repository also includes a discussion forum open for comments and improvement suggestions.
For any questions about the product or the project please contact info(at)aodn.org.au