Overview ========== Acoustic Doppler Current Profilers (ADCPs) use the Doppler shift of an outgoing frequency along a beam to return measured velocity along that beam. ADCPs typically have 4 beams, allowing measurement of velocity in 3 dimensions, in bins of varying distance from the transducer head. In this application, the ADCP is mounted on a CTD rosette frame and lowered along with the rest of the package, hence called Lowered ADCP ("LADCP"). The goal is to determine water velocities to the full depth of the ocean for each deployment. Ocean velocities are very small (few cm/s), especially in the deep water. The package is typically lowered or raised at 1m/s for much of the water column, creating a challenging data processing situation. Lowered ADCP data requires ancillary information to improve the processed data product. Over generations, the processing has improved and these ancillary components are systematically collected along with the LADCP data. In older datasets, they may be missing entirely. The directory structure and naming convention for the submitted LADCP datasets (WOCE+CLIVAR) attempt to rationalize 20 years of data acquisition and processing by a collection of scientists who were inventing the field of LADCP acquisition and processing, so there is some variety in the organization and naming of the orginal datasets. Evolution of the instrumentation and processing techniques have continued. Each data submission is at the "cruise" level, matching the CCHDO cruise legs and CTD station+cast nomenclature. Each data submission contains three directories: - docs: cruise metadata, renaming (if applicable) notes or reports that could be found - raw-level0: original data required to reprocess (all that could be found) - processed-level1: original files produced (if ascii) or netCDF conversion (if matlab) raw-level0 directory: The raw data can be considered to be "level 0", i.e. original data from an instrument. The goal of the level-0 data is that someone would be able to take modern processing techniques and apply them to older datasets. processed-level1: The processed data can be considered to be "level 1", i.e. algorithms combining data from ancillary measurements along with the LADCP data, transformations and editing, and other algorithms are applied along with some quality control, to create a profile of ocean velocity. These data products are the "state of the art at the time"; they have not been reprocessed with modern methods. Note that different processing methods contain different tools to estimate errors--these are contained in the datasets and are accessible to users. Users should be cautioned: LADCP velocities are likely to be most reliable in regions with strong scattering and strong currents. In regions with low scattering and weak currents, for example the center of any ocean gyre and below the main thermocline, LADCP velocities are likely to be suspect. level-2-products: There is no level-2 submission at present. Level-2 data would be robust enough that there are no particluar caveats about using any of it, and errors would be quantified and documented. Details: =========== * directory = "docs" ===================== - cruise_meta.txt: computer-readable file # PI, WOCE Expocode, cruisename, etc - *_ladcpmeta.txt: table of instrument settings (where data exist) - stacast_*rename: notes about file renaming "downlooker" (downward-looking instrument: renaming files) "uplooker" (upward-looking instrument: renaming files) "ctd_timeseries" (rationalization of ctd timeseries names) "inverse" (acquisition did not follow CTD names; processed using 'inverse method') "shear" (acquisition *did* follow CTD names; processed using 'shear' method) "gps_timeseries" (rationalization of gps timeseries names) "depth_soundspeed"(rationalization of depth-soundspeed names) - anything else : notes, reports, or journals about the cruise * directory = "raw-level0" =================================== Over time, processing algorithms have improved and ancillary data have been added. instrument what is gained --------------- ----------------------- Lowered ADCP (+internal heading) (shear profile) + position (start and end) barotropic component + CTD time series accurate depth and speed of sound + shipboard ADCP constraint (surface velocities) + position timeseries (not just start/end) inversion processing method + accelerometer vertical velocity Differences in data acquisition strategy and naming convention over the years means that the original LADCP data file might not match the official CCHDO CTD station and cast. Files have been renamed to match CTD station and cast, and records have been kept to connect the original file name to the submitted file name. Sometimes an instrument fails and another (sometimes a different frequency) is used for the duration of the cruise. In newer cruises there might be an upward-looking and a downward-looking instrument for a single cast. The organization of the raw data reflects this and tries to unify and describe the data across the 25 years and 53 WOCE and CLIVAR cruises. directories: ================ * directory = docs ------------------- cruise_meta.txt # PI, WOCE Expocode, cruisename, etc stacast_*rename # notes about file renaming [any digital journal or notes kept at sea] * directory = raw-level0 ---------------------------- sta = station number cast = cast number - ctd_timeseries ctd_timeseries_00056_001.txt ctd_timeseries_%05d_%03d.txt % (station, cast) # no gps ctd_timeseries_00036_001_gps.txt ctd_timeseries_%05d_%03d_gps.txt % (station, cast) # with gps - depth_soundspeed depth_soundspeed_00019_002.txt depth_soundspeed_%05d_%03d.txt % (station, cast) # if it exists - gps_timeseries gps_timeseries_00019_002.txt gps_timeseries_%05d_%03d.txt % (station, cast) # if it exists - ladcp_raw/ [downlooker,uplooker] BB150, WH150, WH300 example files: ladcp_raw/downlooker/WH150/DLWH15000073_001.PD0 ladcp_raw/downlooker/WH150/DLWH15000073_001.PD0 ladcp_raw/uplooker/WH300/ULWH30000073_001.PD0 ladcp_raw/downlooker/BB150/DLBB15000073_001.PD0 ladcp_raw/downlooker/WH150/DLWH15000073_001.PD0 ladcp_raw/uplooker/WH300/ULWH30000073_001.PD0 ladcp_raw/uplooker/WH300/ULWH30000073_001.PD0 - sadcp_nc # shipboard ADCP at the station wh300, nb150, os150bb, os150nb, # directory named by instrument os75bb, os75nb, os38bb, os38nb] A%-5d%03d.nc (station_cast) For the complete processed shipboard ADCP data, go to JASADCP * directory = processed-level1 ================================= cruise docs cruise_meta.txt # PI, WOCE Expocode, cruisename, etc stacast_*rename # notes about file renaming [any digital journal or notes kept at sea] proc inverse_Visbeck [I00123.002.nc] I%05d_%03d.nc % (station, cast) inverse_Visbeck_Thurnherr [I00123.002.nc] I%05d_%03d.nc % (station, cast) shear_Firing [S00123.002.nc] S%05d_%03d.nc % (station, cast) example: 2008_I6S/proc/inverse_Visbeck/I00045_001.nc 2008_I6S/proc/shear_Firing/S00045_001.nc 2008_I6S/data/ladcp_raw/downlooker/BB150/DLBB15000045_001.PD0 2008_I6S/data/ctd_timeseries/ctd_timeseries_00045_001_gps.txt 2008_I6S/data/sadcp_nc/nb150/A00045_001.nc 2008_I6S/data/gps_timeseries/gps_timeseries_00045_001.txt 2008_I6S/data/depth_soundspeed/depth_soundspeed_00045_001.txt ============================================ References ---------- Two primary processing mechanisms have been used: 'shear' and 'inverse'. References are : - shear Fischer, J., and M. Visbeck. 1993. “Deep Velocity Profiling with Self-Contained ADCPs.” Journal of Atmospheric and Oceanic Technology 10 (5): 764–73. https://doi.org/10.1175/1520-0426(1993)010<0764:DVPWSC>2.0.CO;2. - inverse Visbeck, Martin. 2002. “Deep Velocity Profiling Using Lowered Acoustic Doppler Current Profilers: Bottom Track and Inverse Solutions.” Journal of Atmospheric and Oceanic Technology 19 (5): 794–807. https://doi.org/10.1175/1520-0426(2002)019<0794:DVPULA>2.0.CO;2. Other resources: JASADCP:Primary USA archive for processed shipboard ADCP data (Joint Archive for Shipbord ADCP) http://ilikai.soest.hawaii.edu/sadcp/ USA archive for WOCE, CLIVAR, and GOSHIP hydrographic measurements https://cchdo.ucsd.edu ============================================ File formats: suffix file format ------- --------------- .txt Ascii text .rst Ascii text ("Restructured Text markdown language) .pdf Portable Document Format (PDF) .s text: Linux bash commands (ascii) .nc Network Common Data Format (NetCDF) .PD0 (Note 1) Instrument manufacturer format, see below .NB0 (Note 2) Instrument manufacturer format, see below ** Note 1 - PD0 data format for workhorse and broadband instruments - WorkHorse_Commands_and_Output_Data_Format_Mar16_957-6156-00.pdf ** Note 2 - - PD0 data format for narrowband instruments - NB_VM_Tech_Manual_67119_-_Data_Format.pdf