Four inexpensive current drogues (drifters) were designed and built at the CHL Field Research Facility (FRF) that used GPS tracking and radio telemetry for positioning. Deployments were made on 22-23 March, 5-6 June, and 6-7 June.
Resource Description: NODC Accession Number 0050188
ACKNOWLEDGEMENTS: The field data collection study of the Kuhio Bay, Hilo, Hawaii was performed for the U.S. Army Engineer District, Pacific Ocean, Honolulu (CEPOH) with support from the U.S. Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory's (CHL) Field Research Facility (FRF).
Deployments were on 21 Mar 2007 and retrieved on 5 Jun 2007. All three ADCPs were believed to have "Waves" firmware installed prior to deployment but two were found on site to be only capable of current measurements. ADCP-1, closest to the entrance was selected for wave and current collection, the other two only collected currents. Visual observations of waves at ADCP sites 2 and 3, and analysis of data collected at 1, indicate that typical wave heights at sites 2 and 3 were too low (often < 0.4m) for reliable directional wave estimates to be made with these instruments. ADCP-3 operated only 20 days before the batteries were depleted on 7 April. That unit may have been damaged during shipping.
Wave spectra were computed using the RDI WavesMon v2.1 analysis program. This package computes non-directional spectra from three different parameters; the subsurface orbital velocity, the surface detection signal, and the pressure sensor (VSpec, SSpec, and PSpec respectively). The velocity data are used to compute directional spectra. The WavesMon program outputs ASCII files for each spectra (4 per hourly collection) which are reprocessed using the FRF ADCP analysis programs that combines the three non-directional spectra into a single files and reformats the directional spectra files. The FRF programs also extracts the current profile data, computes various parameters like vertically integrated currents and QC information on the wave analysis.
Spectral processing was done on 4096 point (~34 minute) records, band averaged to 128 frequency points, and directional spectra with 90 directional bins. WavesMon program corrected data for instrument tilt and current Doppler shifted the wave frequency. Additional processing with the FRF package computes QC parameters like spectral signal to noise ratio(SN, log_10 of the ratio), and ratios of surface corrected Hmo values from the three spectra (VSpec, SSpec, and PSpec). It is left up to the user to decide what values to reject data, but typically a SN of less than 2, or Hmo ratios less than 0.8 or more than 1.2 may be suspect.
Current Drogues: Four inexpensive current drogues (drifters) were designed and built at the CHL Field Research Facility (FRF) that used GPS tracking and radio telemetry for positioning. They were constructed with off the shelf plumbing supplies (PVC pipe, vertical risers, rubber unions, hose clamps), a Garmin Geko GPS receivers, and MaxStream (model XStream-PKG-R) radio modems (Figure 4). The sails were approximately one meter in cross-section. The lower vertical PCV pipe (submerged) contained the modem and batteries, the upper horizontal pipe contained the GPS receiver, radio antenna, and LED light. A NEMA GPS data string was transmitted by the GPS to a custom circuit that added a buoy identifier the NEMA string and retransmitted to the FR modem every 20 seconds. Each buoy radio transmission was separated in time by 2s so radio collisions were avoided. Each Garmin GCP unit internally recorded positions every 5 seconds. These GPS units were WAAS enabled and have a horizontal accuracy of about ~2 m. Radio reception required line of sight, which was not always available, and transmission were often missed. The realtime transmitted signals were only used to buoy retrieval, the internally recorded data was used for analysis.
Drogue Track Processing: Current speed and direction were computed from the 30-second internally recorded coordinates. These coordinates are recorded to 3 significant decimal places in lat/lon minutes, or about 2m which is near the WAAS accuracy. To reduce errors and clean up the data these coordinates were smoothed with a 5-minute phase preserving band-averaging filter. Another technique sometimes used for filtering the data is to polynomial fit the points, which provides a smoother estimate but for these tracks the band-averaging method worked best. The band-averaged method was used on all drogue tracks after removing obvious bad data points. Speed and direction values were computed between each filtered data point, with time and position averaged between adjacent points. This resulted in estimated values every 50-s, unless there was a data gap, of which there were few.
INSTRUMENT TYPES: bottom-fixed ADCP with depth, temperature, and wave sensors drifters
REFERENCES: Similar instruments and procedures are described in: Hathaway, K. K and S. Boc, 2008. Field Data Collection Study Final Report: Natatorium Current Study, Waikiki, HI. U.S. Army Engineering POH District, Honolulu, HI., ERDC/CHL TR-08. 55p.
Note: all times are in UTC
within ../data/
0-data/ : This directory contains the original set of directories and files 1-data/ : Directories and files prepared by NODC (such files are prepared if original formats are non-proprietary)
Contents of 0-data/: Directory hilo/:
file: comments: Hilo.analysis-1.doc MS Word document: draft technical report
subdirectorys in hilo/ subdirectory: adcp1/
files: HI040.sum.20070322-20070605.txt HI040adc_20070322_20070608.meta comment: Deployment summaries from instrument configuration files
file: HI040adc_vac_2007_mm.txt (mm=month, ie, 03, 04, 05, 06) comment: Vertically averaged current (VAC) by month. Uave = positive going eastward (mm/s), Vave = positive going north (mm/s).
file: HI040adc_wmo_2007_03_22.log comment: WavesMon format number 5, as follows
Updated with each burst of waves data. Ascii text, comma or space delimited line for each burst of data. Like Format 3 only it outputs a full resolution profile.
Burst#,YY,MM,DD,HH,mm,ss,cc,Hs(m),Tp(s),Dp(deg),Depth(mm),Hmax (m),Tmean(s),bins,depthlevel1Magnitude(m/s),depthlevel1Direction(deg),..., depthlevelNMagnitude(m/s),depthlevelNDirection(deg)
Symbols: YY Year MM Month DD Day HH Hour mm Minute ss Second cc 1/100ths seconds Hs Significant Wave Height = 4*sqrt(area under the power spectrum) Tp Peak period = Wave period associated with the largest peak in the power spectrum Dp Peak Direction = peak direction at the peak period.
file: readAdcpDSpec.m comment: Matlab code snippet to read directional wave spectra files (DSpec/).
file: HI040.2007mm.asc comment: (mm: month) Current velocity, full profile. See header in file for parameter list.
file: HI040.2007mm.hdr comment: header for the corresponding *.asc file 1st record: number of bins (36) 2nd record: depth (cm) above and below mean water column depth corresponding to each bin. Mean water water column depth is defined as the averaged pressure signal over the entire deployment. 3rd record: start date and time 4th record: end date and time Note, although file says EST, time is UTC
subdirectory: adcp1/Dspec comment: Wave directional spectra files (reformatted) from RDI WavesMon program. One file for each hour. See the Matlab code snippet readAdcpDSpec.m. Units are m^2/Hz/Deg.
Filename example: DSpec.HIAD1.200508092100.UTC.asc comment: Directional spectra for 9 August 2005 at 2100 UTC (NOTE: some files have "EST", instead of "UTC", although all data are relative to UTC.
subdirectory adcp1/Fspec comment: Non-directional ADCP spectra, one file each hour Filename example: VSPspec.Hiad4.200704281200.UTC.asc (if EST, then Eastern Standard Time) This example is for 28 Apr 2007 at 1200 UTC.
Format: Columnar ASCII spectra from ADCP Velocity, Surface, and Pressure (VSP). Energy units are m^2/Hz/Deg, And frequency is in Hz.
subdirectory adcp1/Stats comment: wave and current statistics files by month (03=Mar, 04=Apr, etc.)
file: HI040adc_cur_2007_mm_pfl.mat comment: (by month, mm) Matlab format current profile data Variables: Uave1 = vertically averaged east current (mm/s) Vave1 = vertically averaged north current (mm/s) Ux1 = east current profile (cm/s) Vx1= north current profile (cm/s) depth = nominal depth of center of each bin stime = Matlab time format ASCII text files of all parameters in ../data/1-data/hilo/adcp1/Stats
file: HI040adc_ULcur_2007_mm.mat (by month, mm) comment: Matlab format current profile data, see Matlab_Description_ULcur_files.txt ASCII text files of all parameters in ../data/1-data/hilo/adcp1/Stats
file: HI010adc_wmo_2007_mm_UTC.txt comment: Wave and current profiles, file by month, mm, columnar ASCII, one line per wave collection, space delimited. Format follows: Burst# YY MM DD HH mm ss cc Hs(m) Tp(s) Dp(deg) Depth(mm) Hmax(m) Tmean(s) bins depthlevel1Magnitude(m/s) depthlevel1Direction(deg) depthlevelNMagnitude(m/s) depthlevelNDirection(deg) Symbols: YY Year MM Month DD Day HH Hour mm Minute ss Second cc 1/100ths seconds Hs Significant Wave Height = 4*sqrt(area under the power spectrum) Tp Peak period = Wave period associated with the largest peak in the power spectrum Dp Peak Direction = peak direction at the peak period.
subdirectorys in hilo/ subdirectory: adcp2/ see descriptions above for directory adcp1 Note: in adcp2, only one subdirectory, Stats, as described in adcp1/Stats There are no wave data from adcp2.
subdirectorys in hilo/ subdirectory: adcp3/ see descriptions above for directory adcp1, note data only available for March 22 - April 7. No wave data. For file HI050adc_vacSD_2007_03.txt, same as VAC file description under adcp1/ except includes speed and direction.
subdirectorys in hilo/ subdirectory: drogue/ comment: GPS drogue (drifter) data, 21-23 Mar and 5-7 Jun.
file: gpsFilt-Hiloddmmmyy.dat comment: (ddmmyy: day month year) Drogue data, columnar ASCII, with UTC time and Latitude and longitude minutes (north from Lat 19 degrees N and Lon 155 degrees W). These data were computed from the original recorded data (5s interval), had wild points removed, decimated and filtered. The last two columns are drogue speed (m/s) and direction going towards (degrees positive clockwise from north).