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NDBC Real Time Wave Data Processing and QC/QA

Chung-Chu Teng

National Data Buoy CenterStennis Space Center, MS 39529, USA

Chung-Chu.Teng@noaa.gov

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rNDBC Wave Stations

88 buoys (28 directional waves) and 4 C-MAN stations

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rNDBC 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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rBuoy Wave Measurements

3-m discus buoy 10-m discus buoy 6-m NOMAD buoy

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rNew 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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rNOMAD 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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rC-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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rNondirectional 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 Tmms z 4 20

0

2

Frequency, f

S(f)

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rBuoy Wave Measurement

Ocean waves

Buoy hull motions

Measurements (Sensors)

Onboard processing

Transmission (or storage)

Shoreside processing

Wave data

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rNondirectional 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 fP T Fwh

( )

disp lacem ent spectrum

accelera tion spectrum

f

24

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rNoise Correction

Frequency (f)

S(f)

Low-frequencynoise

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rNDBC 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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rDirectional 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 22 33 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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rDirectional wave algorithm (2)

S f C r r( , ) cos cos

11 1 1 2 2

1 12

2

ra

a b ra

a b

b a b a

10

12

12

20

22

22

11

1 1 21

2 2

1 1

12

;

tan , ; tan ,

θ 1 and θ2: mean and principal wave directionsr1 and r2 : directional energy spreading

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rConfigurations 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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rNDBC 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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rGeneral 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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rSome 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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rHard 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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rSoft 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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rRange check (wave height)

Previous EQC limit: 5.2 m (Lakes Erie and Huron)New EQC limit: 7.5 m

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rRange check (wave period)

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rIncreasing QMEAN

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rHurricane Ivan - Significant wave heights

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rSignificant wave height during Ivan

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rWind and wave directions

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rWind-wave algorithm

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rHow 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