National Data Buoy Center NDBC Real Time Wave Data Processing and QC/QA Chung-Chu Teng National Data...
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Transcript of National Data Buoy Center NDBC Real Time Wave Data Processing and QC/QA Chung-Chu Teng National Data...
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NDBC Real Time Wave Data Processing and QC/QA
Chung-Chu Teng
National Data Buoy Center
Stennis Space Center, MS 39529, USA
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NDBC Wave Stations
88 buoys (28 directional waves) and 4 C-MAN stations
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NDBC wave measurement capabilities
Non-directional waves
Directional waves
3-m, 10-m discus buoys
Yes
(all)
Yes
(28)
6-m NOMAD buoys
Yes
(all)
Plan to use a supplemental directional
wave buoy C-MAN
(in water)
Yes (4, not very reliable)
Plan to use COTS wave sensors or a directional
wave buoy
C-MAN
(on land)-- Plan to use a directional
wave buoy
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C-MAN Wave Measurements
Chesapeake Light Diamond Shoal St. Augustine
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Buoy Wave Measurements
3-m discus buoy 10-m discus buoy 6-m NOMAD buoy
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New Stand-alone Wave System/Buoy
- Small & light- Low power consumption- Low cost- Built-in transmitter- Standalone- Configurable
Directional Wave Measurement System:
Directional Wave buoy:
- Small & light, deployable from small vessels
- Low cost - Low maintenance
1.8 m COLOS buoy
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NOMAD Directional Wave Measurements
Use a small directional wave buoy (tether to a 6-m NOMAD
buoy or stand-alone)
RF/LOScommunication
GOES or Iridium
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C-MAN Wave Measurements
Install a fixed directional wave sensor on the
structure
Deploy a stand-alone directional
wave buoy
RF/LOScommunication
GOES or Iridium
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Nondirectional wave data
• Wave energy spectrum
• Wave parameters:
Peak (or dominant) wave period, Tp
Mean (or average) wave period, Tz or Ta
Significant wave height, Hs
H m and Tm
ms z 4 200
2
Frequency, f
S(f)
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Buoy Wave Measurement
Ocean waves
Buoy hull motions
Measurements (Sensors)
Onboard processing
Transmission (or storage)
Shoreside processing
Wave data
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Nondirectional wave data from buoys
From buoy motion to wave data
Sh(f): spectrum of buoy heave motion
Sw(f): wave spectrum (acceleration)
PTF: power transfer function
From acceleration to displacement spectra
S fS f
P T Fwh
( )
d isp lacem en t spectrum
accelera tion spectrum
f
24
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Noise Correction
Frequency (f)
S(f)
Low-frequencynoise
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NDBC directional wave buoy systems
• Based on the “slope following” principle
• Can only use axis-symmetrical buoys
• Buoy pitch and roll information are required to determine directional wave data
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Directional wave algorithm (1)
S fa
a b
a b
( , ) co s sin
co s sin
01 1
2 2
22 2
a C ak
Q bk
Q
ak
C C bk
C
0 11 1 1 2 1 1 3
2 2 2 2 3 3 2 2 2 3
1 1 1
1 2
; ;
;
f : wave frequency; : wave direction
K: the wave number C and Q : co- and quad-spectra
1: vertical motion (heave)2: N-S slope (pitch)3: W-E slope (roll)
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Directional wave algorithm (2)
S f C r r( , ) co s co s
11 1 1 2 2
1 1
22
ra
a b ra
a b
b a b a
10
12
12
20
22
22
11
1 1 21
2 2
1 1
1
2
;
tan , ; tan ,
θ 1 and θ2: mean and principal wave directionsr1 and r2 : directional energy spreading
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Configurations of NDBC directional wave systems
• HIPPY – a gimbaled gyro system that measure pitch and roll directly
• MO – use only magnetometer outputs to estimate buoy pitch and roll
• ARS – derive buoy pitch and roll from angular rate sensors
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NDBC Wave Systems
• DACT Wave Analyzer (WA)• DACT Directional Wave Analyzer (DWA)• VEEP Wave Analyzer (WA)• Wave Processing Module (WPM)• Directional Wave Processing Module
(DWPM)• Non-Directional Wave Processing Module
(NDWPM)• Directional Wave Measurement System
(DWMS)
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General Principles for Data QA/QC
• Reasonability: Data should be in reasonable ranges and intervals.
• Continuity: Data should maintain the continuity in time and space.
• Consistency (or correlation): Data should have proper time correlation, spatial correlation, and correlations with other measurements.
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Some wave data QC techniques
• Range check• Time continuity• Internal consistency (e.g., QMEAN)• Wind vs. wave energy (wind-wave algorithm)• Swell direction check• High frequency spectral spikes, • Wave height vs. average wave period • Wave direction vs. wind direction (> 0.35 Hz)• When needed, wave data from NCEP’s wave
models and other organizations will be used to check its buoy wave data.
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Hard Flags (by hierarchy - highest to lowest)
• T Transmission parity error (Applies to continuous winds and non-WPM wave data)
• M Missing sensor data (A result of a garbled or missing message).
• W A WPM wave message is short, missing a checksum, or parity errors are detected.
• E Calculation limits are exceeded or are in error (waves only, flags WVHGT).
• D Delete measurement from release and archive (A Data Analyst or automated QC has failed the sensor).
• S Invalid statistical parameter (in waves, QMEAN is not between QMIN and QMAX, flags WVHGT).
• V Failed time continuity. • L Failed range limits. • H Hierarchy reversal has occurred (BARO, WSPD, WDIR
only). • R A related measurement has failed a hard QC check.
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Soft Flags (in alphabetical order)
• a Measurement is above monthly, regional limit.• b Measurement is below monthly, regional limit.• c Measurement has been adjusted, or corrected (applies to DEWPT and WVHGT,
DOMPD and AVGPD). • d Failed standard deviation test (continuous winds only). • f Measurement failed hourly time continuity. • g Failed gust-to-mean wind speed ratio (applies to standard and continuous winds). • i Continuous and hourly wind speeds don’t agree. • j One, and only one, transmission error detected in the continuous wind string of a
GOES message (all continuous wind measurements are flagged, if more than one error detected, than flag is upgraded to a T flag).
• k Difference between duplicate measurements is too high. • m High frequency spikes detected in the wave spectrum (C11), WVHGT is flagged. • n Measurement failed comparison with NCEP model fields. • p Failed wave height to wave period comparison test.• q Swell direction is from an improbable direction.• r Related measurement failed (continuous winds only).• s Stuck raw compass ( RCOMP and WDIR are flagged).• t Tendency difference between duplicate sensors is too high.• v Failed relative humidity verses visibility check.• w Failed wind direction verses wave direction check.• x Wind wave energy is too high for prevailing wind speed.• y Wind wave energy is too low for prevailing wind speed.• z Failed bow azimuth verses wind direction check.
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Handbook of Automated Data Quality ControlChecks and
Procedures of the National Data Buoy Center
February 2003
National Data Buoy Center
Stennis Space Center, Mississippi 39529-6000
NDBC Technical Document 03-02
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Range check (wave height)
Previous EQC limit: 5.2 m (Lakes Erie and Huron)New EQC limit: 7.5 m
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Range check (wave period)
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Increasing QMEAN
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Hurricane Ivan - Significant wave heights
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Significant wave height during Ivan
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Wind and wave directions
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Wind-wave algorithm
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How is your wave measurement?
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We always improve our systems and DQC/QA process so we can get more
accurate wave measurement