RESEARCH VESSELS - ACOUSTIC DOPPLER CURRENT PROFILER (ADCP) DATA

P. Caldwell (NOAA/NODC/SAC, USA)

Announced availability: 1 May 1995

Data Access

Shipboard Acoustic Doppler Current Profiler (ADCP) data are available from the National Oceanographic Data Center's (NODC) Shipboard ADCP Center (SAC), established at the University of Hawaii. Data can be accessed via anonymous FTP from http://www.soest.hawaii.edu/COARE/. A subset of these data can also be accessed through the URL http://www.soest.hawaii.edu/COARE/. CODAS software is available via anonymous FTP from noio.soest.hawaii.edu in subdirectory pub/codas3.

Background

ADCP Data Collection
The hull-mounted ADCP estimates horizontal and vertical velocity as a function of depth by using the Doppler effect to measure the radial relative velocity between the instrument and scatterers in the ocean. Three acoustic beams in different directions are the minimal requirement for measuring the three velocity components. A fourth beam adds redundancy and an error estimate. The ADCP transmits a ping from each transducer element roughly once per second. The echo arrives back at the instrument over an extended period, with echoes from shallow depths arriving sooner than ones from greater ranges. Profiles are produced by range-gating the echo signal, which means the echo is broken into successive segments called depth bins. These correspond to successively deeper depth ranges. The operator configures the length of each depth bin and transmit pulse, which determines the degree of averaging in the vertical, depending on whether one is more interested in vertical resolution or profile penetration. The noisy velocity estimates from each ping are vector-averaged into 1-minute to 10-minute ensembles. The relative velocities are rotated from the transducer's reference to the earth's reference frame using the ship's gyrocompass. Finally, relative velocities and various ancillary parameters are stored on the ship using a data acquisition system (DAS). The DAS optionally records navigation information, such as provided by the GPS. Specifics of the instrument capabilities and configuration options are well documented (RDI, 1989).

Routine processing, quality control, and calibration are performed at the host institute. Standard checks include: detecting and correcting time errors, applying transducer-level temperatures and salinities to obtain a better estimate of the sound speed for the velocity calculation, editing out bad bins or profiles that have been contaminated by interference with the bottom (or some other physical object such as a hydro wire), and verifying the quality of the gyrocompass and the navigation data. The final gyrocompass estimates of the ship's heading and navigation information are the primary sources for calibrating the ADCP's relative current velocities. Typically, one is correcting for an "angle " error due to misalignment of the transducer relative to the ship's hull, and an "amplitude" component related mostly to minor imperfections of the transducer geometry. Relative current velocity errors caused by these components are orthogonal; the angle errors lead to uncertainties of the athwartship's velocity component, while the amplitude error introduces uncertainties along the ship track.

The navigation calculation is performed once calibration is complete. Absolute currents over a fixed-depth range (reference layer) are obtained by subtracting the average of the ship velocity relative to a reference layer (i.e., ADCP velocities) from the absolute ship velocity over the ground (from navigation, i.e., GPS). The raw absolute current velocities relative to the reference layer are smoothed to reduce the effects of noise in the position fixes, and combined with the navigation data to obtain the best estimates of ship positions and velocities. Thus, absolute currents at any depth can be determined from the ship's final navigation data and the relative ADCP measurements.

Shipboard ADCP Center at the University of Hawaii
NODC established the SAC at the TOGA Sea Level Center at the University of Hawaii for the acquisition, review, documentation, archival, and distribution of shipboard ADCP datasets. These high-density datasets, which have been passed through quality control, calibration, and navigation stages, are placed in the so-called "CODAS" format (see below). The datasets are then reviewed, reduced to a standard subset, documented, and backed up. SAC will contact data producers if suspect features are identified. Datasets are periodically passed on to NODC headquarters, which acts as the final repository.

CODAS (Common Oceanographic Data Analysis System)
CODAS is a software package that was designed, documented, and maintained by Dr. Eric Firing and associates from the University of Hawaii. The software provides easy access to the data with a variety of options for averaging, regridding, and selecting data that meet specified quality criteria. Overall, CODAS allows the effective handling of high-density datasets that consist of currents and ancillary parameters at the sampling interval with which the data were recorded and processed. It deals well with the volume of data collected (about 10 MB on a typical month-long cruise), cruise-to-cruise variability and intra-cruise variability of the sampling rates and types of ancillary parameters. Ancillary parameters included the date-time group, transducer temperature and salinity, a variety of diagnostic values, heading information, and navigational data. CODAS stores arrays of flags corresponding to the velocity arrays; thus, the original data are not altered by editing.

CODAS is a hierarchical database which uses a "directory file" to keep track of binary "block files." The system was written in standard C language and the package is primarily used on workstations and IBM-compatible PCs. CODAS data extraction subset software and manual are geared to data users. The complete CODAS software and manual are geared to data collectors and processors, and include steps on how to load ping files (data from DAS) and how to process, calibrate, and apply navigation data. Both software sets are available via anonymous ftp (see Appendix) or mail and include a utility for translation of the block files between machines with different binary numbering conventions. A complete ASCII dump of the CODAS block files (about 50 MB per cruise-month) can also be provided.

Data File Information

The shipboard ADCP data are available as two data types:

  • Densely-sampled set (~10 MB per cruise-month) as CODAS binary block files of the currents, and ancillary data at the interval with which the data were recorded and processed, and
  • an ASCII standard subset of the currents, ship's speed, and transducer temperatures at hourly and 10-m depth intervals.

    For each cruise, a metadata file is prepared for summarizing specifics about the instrumentation, cruise activities, data processing, and calibration.

    An inventory browser is available via anonymous ftp for SUN and SGI workstations and for IBM-PC computers using DOS. Within the WWW home page, the On-line Inventory System may also be accessed. Queries of the database or the inventory lists will list SAC IDs for specifying desired cruises, and data can be grabbed from the On-line Database System.

    The standard subset and metadata files are maintained on-line in an anonymous ftp area and are available free of charge. The standard subset format is ASCII.

    Data types, metadata files, inventories, and cruise tracks can be obtained via conventional storage media (diskettes or DAT, eXabyte, or magnetic tapes) for a fee. The densely-sampled dataset can be made available on anonymous FTP on a case-by-case basis. In general, NODC products and services are provided on a cost recovery basis. However, researchers who submit data to NODC are eligible to receive NODC data on exchange. For charges, consult the SAC URL (http://ilikai.soest.hawaii.edu/sadcp/obtain.html)or contact Patrick Caldwell.

    Inventory - COARE Research Vessels 

    SAC_ID PLATFORM              STARTDATE ENDDATE
LONGITUDE_RANGE LATITUDE_RANGE PI

00001  wecoma (w9211a)       92/11/08  92/12/08
144.58E-158.20E  2.71S-13.45N  huyer
00002  wecoma (w9211b)       92/12/12  93/01/15
144.59E-158.17E  2.61S-13.45N  hacker
00003  wecoma (w9211c)       93/01/23  93/02/17
149.34E-158.18E  2.49S- 9.83N  hacker
00004  moana (mw9218)        92/10/27  92/12/07
144.58E-157.93W  1.84S-21.27N  gregg
00005  noroit (coare-poi)    92/12/02  93/02/28
152.17E-166.83E 22.23S- 7.04N  eldin
00006  moana (mw9301)        93/01/22  93/02/21
144.55E-156.16E  1.82S-13.46N  gregg
00007  moana (mw9302)        93/03/03  93/03/31
144.59E-170.06E  7.98S-13.43N  lukas
00012  moana (mw9219)        92/12/13  93/01/16
144.57E-156.11E  1.99S-13.46N  moum
00036  moana (mw9411)        94/04/11  94/05/11
137.01E-165.26E  8.04S-13.47N  lukas
00037  moana (mw9205)        92/04/17  92/05/14
136.95E-171.00E  3.33S-13.45N  lukas
00078  franklin (fr0992)     92/11/18  92/12/16
147.09E-156.17E 18.23S- 1.56S  godfrey
00079  franklin (fr0193)     93/01/08  93/02/08
146.09E-157.54E 18.28S- 1.30S  godfrey
00084  xiang (xyh5_leg1)     92/11/06  92/12/01
154.23E-159.34E  6.95S- 1.81S  pu
00085  xiang (xyh5_leg2)     92/12/14  93/01/08
154.72E-159.68E  7.29S- 1.84S  pu
00086  xiang (xyh5_leg3)     93/01/23  93/02/22
144.70E-155.98E  2.52S-12.43N  pu
00087  shiyan3 (sy3l1(leg1)) 92/11/07  92/12/13
154.92E-160.42E  7.74S- 1.00S  chen
00088  shiyan3 (sy3l2(leg2)) 92/12/16  93/01/24
157.75E-160.50E  9.43S- 2.06S  chen
00089  shiyan3 (sy3l3(leg3)) 93/01/28  93/02/19
154.11E-160.51E  9.43S- 1.03S  chen
00126  kexue (kex1~(leg1))   92/11/09  92/12/11
155.84E-156.21E  4.05S- 3.71S  Hu
00127  kexue (kex2~(leg2))   92/12/18  93/01/23
155.84E-156.65E  4.38S- 3.77S  Hu
00128  kexue (kex3~(leg3))   93/01/31  93/02/19
156.13E-156.76E  4.56S- 4.05S  Hu
00131  vickers (leg_1)	     92/11/11  92/12/10
156.12E-156.67E  2.62S- 1.50S  Pinkel
00132  vickers (leg_2)	     92/12/22  93/01/19
156.12E-156.39E  2.33S- 1.96S  Pinkel
00133  vickers (leg_3) 	     93/01/30  93/02/26
155.20E-156.49E  2.47S- 1.78S  Pinkel


moana = Moana Wave
noroit = Le Noroit
xiang = Xiangyanghong #5
kexue = Kexue #1
vickers = John V. Vickers
    Information available within the NODC/SAC anonymous FTP area: 

     Directory             Comment
 -------------------   -----------------------------------
 INVNTORY              Inventory lists, cruise track plots
 DATABASE              standard subsets, cruise tracks, and
                       cruise summary files for each cruise
                      *if you obtain files, please email me
                       and let me know what you grabbed, thanks.
                       caldwell@soest.hawaii.edu
 BIRS                  Browse, Inventory, and Retrieval
 Software.
                       Available for public queries of global
                       database.  See instructions below.
 GEN_DOC               General documentation and overview
 ASC_DUMP              Software for ASCII dump of CODAS
 dataset
 CODAS_MN              1) a compressed post-script "rough
 draft"
                       of processing manual and 2) "second draft"
                       of NODC's Access to High-Resolution CODAS
                       Shipboard ADCP Data
 SUBMIT                ATTENTION DATA CONTRIBUTORS
                       metadata is invaluable, to assist in
                       preparation for your submission, see
                       this subdirectory for a
                       a blank form and an example
 SAMP_SUB              Sample files for NODC subset
 ESM                   Article for NOAA's Earth System
 Monitor
 xfer_dat              Working area for data transfer
    Filenames are as follows: 

        read_1st.doc               This file - explains file names
    size.lis                   A summary of file sizes within
    transfer
                               subdirectory -- we suggest you download
                               this file first to estimate transfer time
    std_sub.doc                Standard subset format
    description
    cru_trk.doc                Cruise track format description
    dist_pol.doc               NODC shipboard ADCP distribution
    policy
    *.inv                      Inventory file
    sssss.sub                  Standard subset (hourly and 10 m
    depth intervals
                               for U,V, transducer temp, and ship U, ship V,
                               for sac_id=sssss, ie. 00123.sub
    sssss.bft                  Cruise summary, or block footer
    as we call it
    sssss.cru                  Cruise track at hourly intervals
    sssss.def                  Producer definition file, used
    during conversion
                               of CODAS binary dataset from one machine type
                               to another using CODAS utility mkblkdir
    sssssnnn.blk               CODAS block nnn for cruise sssss
    sssssdir.blk               CODAS block directory for cruise
    sssss
    If high-resolution data (CODAS block files) have been requested, a subdirectory is created for each cruise using the SAC_ID as the directory name. Within this directory, users will find the standard subset (sssss.sub), the cruise summary (sssss.bft), the producer definition file (sssss.def), and the CODAS block and block directory files.

    If workstations other than SUN or SGIs are used, the CODAS binary files have to be converted to conform to the machine type using CODAS "mkblkdir" utility.

    For processing ADCP data, the user is referred to the demo in codas3/adcp/demo. More detailed descriptions of the programs themselves are in the source subdirectories. A more cohesive manual for ADCP processing is underway. In the meantime, the user may also download the file whp/opmeth.ps which can be sent to a PostScript printer. It provides an overview of the ADCP Processing System.

    Note that an essential part of the ADCP Processing System requires the commercial program Matlab (by The Math Works, Inc.), which the user must acquire separately. The contour plotting program is also available by anonymous ftp from this site (contour.tar.Z) but only for the Sun workstation at the present time.

    For more information, please contact:

    Patrick Caldwell
    NODC Hawaii Liaison Officer
    Shipboard ADCP Center
    Dept. of Oceanography
    University of Hawaii, MSB 317
    Honolulu, Hawaii 96822
    USA

    email: caldwell@soest.hawaii.edu
    Phone: (808) 956-4105
    FAX: (808) 956-4104

    Appendix

    Instructions for obtaining the complete CODAS software package

    The CODAS source code, libraries, executables, documentation and demo are archived as codas3.exe (PC version) and codas3.tar.Z (Sun4 version). They are available via anonymous FTP from noio.soest.hawaii.eduin subdirectory pub/codas3.

    The archives are around 5 to 6 MB, and de-archive into roughly 15 MB of disk space.

    To de-archive the Sun version: 

       % zcat codas3.tar.Z | tar xvf -
    This will create a codas3 subdirectory in the current directory.

    To de-archive the PC version: 

    
   C:> codas3 -d
    For processing ADCP data, refer to the demo in codas3/adcp/demo. More detailed descriptions of the programs are in the source subdirectories. A more cohesive manual for ADCP processing is underway. In the meantime, download the file whp/opmeth.ps, which can be sent to a PostScript printer. It provides an overview of the ADCP Processing System.

    Be sure to modify your search path to find the executables: 

       ./codas3/bin/sun4  (for the Sun)
   .\codas3\bin\pc    (for the PC)
    Note that an essential part of the ADCP Processing System requires the commercial program Matlab (by The Math Works, Inc.), which must be acquired separately. The contour plotting program is also available for Sun workstations by anonymous FTP from this site (contour.tar.Z).

    Forward inquiries and problems to Mrs. Julie Ranada (julier@soest.hawaii.edu) or Patrick Caldwell (caldwell@soest.hawaii.edu).

    Return to Ship Data Overview
    Return to TOGA COARE Data User's Guide Table of Contents
    Return to the COARE Homepage