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NOAA
requests that use of this data in published reports or presentations
reference the source of the data as "NOAA’s National Data Buoy
Center".

Measurement Descriptions and Units

Note: Station pages display the current hour's measurements in English
units by default, but can be changed by the viewer to metric units. When
accessing Real Time and Historical data files, the measurements are
generally in metric units, as described below, and cannot be
changed.

STATION ID

Five-digit WMO Station Identifier
used since 1976. ID's can be reassigned to future deployments within
the same 1 degree square.

DATE

In UTC (formerly called Greenwich Mean Time - GMT)

TIME

In UTC for data files/display. Station pages show current
observations in station local time by default, but can be changed by
the viewer to UTC. See the Acquisition Time help topic for a more
detailed description of observation times.

Data are classified according to the following groups. Any data field
that contains "9 filled" represents missing data for that observation
hour. (Example: 999.0 99.0)

Standard Meteorological Data

WDIR

Wind direction (the direction the wind is coming from in degrees
clockwise from true N) during the same period used for WSPD. See Wind Averaging
Methods

WSPD

Wind speed (m/s) averaged over an eight-minute period for buoys
and a two-minute period for land stations. Reported Hourly. See Wind Averaging
Methods.

GST

Peak 5 or 8 second gust speed (m/s) measured during the
eight-minute or two-minute period. The 5 or 8 second period can be
determined by payload, See the Sensor Reporting,
Sampling, and Accuracy section.

WVHT

Significant wave height (meters) is calculated as the average of
the highest one-third of all of the wave heights during the
20-minute sampling period. See the Wave Measurements
section.

DPD

Dominant wave period (seconds) is the period with the maximum
wave energy. See the Wave Measurements
section.

APD

Average wave period (seconds) of all waves during the 20-minute
period. See the Wave
Measurements section.

MWD

Mean wave direction corresponding to energy of the dominant
period (DPD). The units are degrees from true North just like wind
direction. See the Wave Measurements
section.

PRES

Sea level pressure (hPa). For C-MAN sites and Great Lakes buoys,
the recorded pressure is reduced to sea level using the method
described in NWS Technical Procedures Bulletin 291
(11/14/80).

ATMP

Air temperature (Celsius). For sensor heights on buoys, see Hull Descriptions.
For sensor heights at C-MAN stations, see C-MAN Sensor
Locations

WTMP

Sea surface temperature (Celsius). For sensor depth, see Hull
Description.

DEWP

Dewpoint temperature taken at the same height as the air
temperature measurement.

VIS

Station visibility (statute miles). Note that buoy stations are
limited to reports from 0 to 1.9 miles.

PTDY

Pressure Tendency is the direction (plus or minus) and the
amount of pressure change (hPa)for a three hour period ending at the
time of observation.

TIDE

The water level in feet above or below Mean Lower Low
Water (MLLW).

Derived Met Values

HEAT

For more information on heat index, please see the NWS Heat
Wave page.

CHILL

Please note that NDBC uses unadjusted winds to calculate wind
chill. The winds are calculated at anemometer height. For more
information on wind chill, please see the NWS Wind
Chill Temperature Index.

ICE

Estimated ice accretion in inches per hour based on an algorithm
developed by Overland and Pease at the Pacific Marine Environmental
Laboratory in the mid-1980s. The algorithm relates icing to the
presently observed wind speed, air temperature, and sea surface
temperature. The method is designed for trawlers in the 20 to 75
meter length range, underway at normal speeds in open seas and not
heading downwind. In general, NWS forecasters translate ice
accretion rates to the following categories:

light: 0.0 to 0.24 inches of ice accretion/hour;

moderate: 0.25 to 0.8 inches/hour; and

heavy: greater than 0.8
inches/hour.

Supplemental Measurements Data

Lowest 1 minute pressure

Lowest recorded atmospheric pressure for the hour to the nearest
0.1 hPa and the time at which it occured (hour and minute).

Highest 1 minute wind speed

Highest recorded wind speed for the hour to the nearest 0.1 m/s,
its corresponding direction to the nearest degree, and the time at
which it occured (hour and minute).

Continuous Winds

WDIR

Ten-minute average wind direction measurements in degrees
clockwise from true North.

WSPD

Ten-minute average wind speed values in m/s.

GDR

Direction, in degrees clockwise from true North, of the GSP,
reported at the last hourly 10-minute segment.

GST

Maximum 5-second peak gust during the measurement hour, reported
at the last hourly 10-minute segment.

GTIME

The minute of the hour that the GSP occurred, reported at the
last hourly 10-minute segment.

Detailed Wave Summary

WVHT

Significant Wave Height is the average height (meters) of the
highest one-third of the waves during a 20 minute sampling
period.

SWH

Swell height is the vertical distance (meters) between any swell
crest and the succeeding swell wave trough.

SWP

Swell Period is the time (usually measured in seconds) that it
takes successive swell wave crests or troughs pass a fixed
point.

SWD

Swell Direction is the compass direction from which the swell
wave are coming from.

WWH

Wind Wave Height is the vertical distance (meters) between any
wind wave crest and the succeeding wind wave trough (independent of
swell waves).

WWP

Wind Wave Period is the time (in seconds) that it takes
successive wind wave crests or troughs to pass a fixed point.

WWD

Wind Wave Direction is the compass direction (degrees) from
which the wind waves are coming.

Steepness

Wave steepness is the ratio of wave height to wave length and is
an indicator of wave stability. When wave steepness exceeds a 1/7
ratio; the wave becomes unstable and begins to break.

APD

Average Wave Period is the average period (seconds) of the
highest one-third of the wave observed during a 20 minute sampling
period.

MWD

Mean wave direction corresponding to energy of the dominant
period (DOMPD). The units are degrees from true North just like wind
direction. See the Wave Measurements
section.

Spectral Wave Data

Spectral wave density

Energy in (meter*meter)/Hz, for each frequency bin (typically
from 0.03 Hz to 0.40 Hz).

Spectral wave direction

Mean wave direction, in degrees from true North, for each
frequency bin. A list of directional stations
is available.

Directional Wave Spectrum

= C11(f) * D(f,A), f=frequency (Hz), A=Azimuth angle measured
clockwise from true North to the direction wave is from.
D(f,A) =
(1/PI)*(0.5+R1*COS(A-ALPHA1)+R2*COS(2*(A-ALPHA2))). R1 and R2 are
the first and second normalized polar coordinates of the Fourier
coefficients and are nondimensional. ALPHA1 and ALPHA2 are
respectively mean and principal wave directions.
In terms of
Longuet-Higgins Fourier Coefficients

R1 =
(SQRT(a1*a1+b1*b1))/a0

R2 =
(SQRT(a2*a2+b2*b2))/a0

ALPHA1 =
270.0-ARCTAN(b1,a1)

ALPHA2 =
270.0-(0.5*ARCTAN(b2,a2)+{0.
or 180.})

Note! The R1 and R2 values in the monthly
and yearly historical data files are scaled by 100, a
carryover from how the data are transported to the archive centers.
The units are hundredths, so the R1 and R2 values in those files
should be multiplied by 0.01.

For more information on the mathematics behind the measuring of surface
water waves, see the waves help section.

Ocean Current Data

DEP01,DEP02,...

The distance from the sea surface to the middle of the depth
cells, or bins, measured in meters.

DIR01,DIR02,...

The direction the ocean current is flowing toward. 0-360
degrees, 360 is due north, 0 means no measurable current.

SPD01,SPD02,...

The speed of the ocean current measured in
cm/s.

Ocean Current Data (Expanded ADCP format)

Instrument Number

Stations may have more than one ADCP instrument. This field
distinguishes these instruments by number. Valid values are 0-9,
with 0 being reserved for surface measurements.

Bin

The bin number, ranging from 1 to 128, where 1 is the bin
closest to the transducer head.

Depth

The distance from the sea surface to the middle of the depth
cells, or bins, measured in meters.

Dir

The direction the ocean current is flowing toward. 0-360
degrees, 360 is due north, 0 means no measurable current.

Speed

The speed of the ocean current measured in cm/s.

ErrVl

The error velocity measured in cm/s.

VerVl

The vertical velocity of the ocean current measured in
cm/s.

%Good3

The percentage of three-beam solutions that are good.

%Good4

The percentage of four-beam solutions that are good.

%GoodE

The percentage of transformations rejected.

EI1,EI2,EI3,EI4

The echo intensity values for the four beams. Valid values are 0
to 255.
EI1 = Echo Intensity for beam #1;
EI2 = Echo Intensity
for beam #1;
EI3 = Echo Intensity for beam #3; and
EI4 = Echo
Intensity for beam #4.

CM1,CM2,CM3,CM4

The correlation magnitude values for the four beams. Valid
values are 0 to 255.
CM1 = Correlation Magnitude for beam
#1;
CM2 = Correlation Magnitude for beam #1;
CM3 = Correlation
Magnitude for beam #3; and
CM4 = Correlation Magnitude for beam
#4.

Flags

The nine quality flags represent the results of the following
quality tests based on their position in the flags field.

Flag 1 represents the overall bin status.
Flag 2 represents
the ADCP Built-In Test (BIT) status.
Flag 3 represents the Error
Velocity test status.
Flag 4 represents the Percent Good test
status.
Flag 5 represents the Correlation Magnitude test
status.
Flag 6 represents the Vertical Velocity test
status.
Flag 7 represents the North Horizontal Velocity test
status.
Flag 8 represents the East Horizontal Velocity test
status.
Flag 9 represents the Echo Intensity test status.

Valid values are:
0 = quality not evaluated;
1 = failed
quality test;
2 = questionable or suspect data;
3 = good
data/passed quality test; and
9 = missing
data.

For more information on continuous winds and the timing of these
measurements, see the continuous winds help
section.

Marsh-McBirney Current Measurements

DIR

Direction the current is flowing TOWARDS, measured in degrees
clockwise from North.

SPD

Current speed in cm/s.

Water Level

TG01, TG02,...,TG10

Six-minute water levels representing the height, in feet, of the
water above or below Mean Lower Low Water (MLLW), offset by 10 ft.
to prevent negative values. Please subtract 10 ft. from every value
to obtain the true water level value, in reference to
MLLW.

Oceanographic Data

Depth (DEPTH)

Depth (meters) at which measurements are taken.

Ocean Temperature (OTMP)

The direct measurement (Celsius) of the Ocean Temperature (as
opposed to the indirect measurement (see WTMP above)).

Conductivity (COND)

Conductivity is a measure of the electrical conductivity
properties of seawater in milliSiemens per centimeter.

Salinity (SAL)

Salinity is computed by a known functional relationship between
the measured electrical conductivity of seawater (CON), temperature
(OTMP) and pressure. Salinity is computed using the Practical
Salinity Scale of 1978 (PSS78) and reported in Practical Salinity
Units.

Oxygen Concentration (O2%)

Dissolved oxygen as a percentage.

Oxygen Concentration (O2PPM)

Dissolved oxygen in parts per million.

Chlorophyll Concentration (CLCON)

Chlorophyll concentration in micrograms per liter (ug/l).

Turbidity (TURB)

Turbidity is an expression of the optical property that causes
light to be scattered and absorbed rather than transmitted in
straight lines through the sample (APHA 1980). Units are Formazine
Turbidity Units (FTU).

pH (PH)

A measure of the acidity or alkalinity of the seawater.

Eh (EH)

Redox (oxidation and reduction) potential of seawater in
millivolts.

Solar Radiation Data

Shortwave Radiation
(SRAD1,
SWRAD)

Average shortwave radiation in watts per square meter for the
preceding hour. Sample frequency is 2 times per second (2 Hz). If
present, SRAD1 is from a LI-COR LI-200 pyranometer
sensor, and SWRAD is from an Eppley PSP Precision Spectral
Pyranometer.

Longwave Radiation (LWRAD)

Average downwelling longwave radiation in watts per square meter
for the preceding hour. Sample frequency is 2 times per second (2
Hz). If present, LWRAD is from an Eppley PIR Precision Infrared
Radiometer.

DART Measurements

T (TYPE)

Measurement Type:

1 = 15-minute measurement;

2 = 1-minute measurement; and

3 = 15-second measurement.

HEIGHT

Height of water column in meters.

24-Hour Rain Measurements

24-Hour Rain Rate

Average precipitation rate in units of millimeters per hour over
24-hour period from 00:00 to 23:59.99 GMT.

24-Hour Rain Accumulation

Total accumulation of precipitation in units of millimeters on
station over 24-period from 00:00 to 23:59.99 GMT.

Percent Time Raining in 24-Hour Period

Percentage of 144 ten-minute periods within a 24 hour period
with a measurable accumulation of precipitation.

Flag

In the case of 24-hour rainfall measurements, a flag is assigned
when over half of the 10-minute measurements from which it is
derived are flagged.

Hourly Rain Measurements

Hourly Rain Accumulation

Total accumulation of precipitation in units of millimeters on
station during the 60-minute period from minute 0 to minute 59:59.99
of the hour.

Flag

In the case of one-hour accumulation, a flag is assigned when
over half of the 10-minute measurements from which it is derived
have been flagged.

10-Minute Rain Measurements

10-Minute Rain Rate

Rain rate in units of millimeters per hour on station over the
10-minute period from 5 minutes before to 4 minutes 59.99 seconds
after the time with which it is associated.

Flag

In the case of 10-minute rainfall measurements, a flag is
assigned to any measurement when either the -5 or +5 minute rain
measurement from which it is derived is missing or obviously an
error.

Discontinued Measurement Abbreviations

Some historical files have column heading abbreviations that have
changed over time. The old abbreviations are listed below with links to
the new standardized abbreviation description.

Old

New Abbreviation

WD

WDIR -
Wind Direction

DIR

WDIR -
10 Minute Wind Direction

SPD

WSPD
- 10 Minute Wind Speed

GSP

GST -
Gust in Continuous Winds data

GMN

GTIME
- Time of Gust in Continuous Winds data

BARO

PRES -
Pressure

H0

WVHT -
Significant Wave Height

DOMPD

DPD -
Dominant Wave Period

AVP

APD -
Average Wave Period

SRAD

SWRAD
- Short Wave Solar Radiation

SRAD2

SWRAD
- LI-COR Short Wave Solar Radiation

LRAD

LWRAD
- Long Wave Solar Radiation

LRAD1

LWRAD
- Long Wave Solar Radiation

U.S. Dept. of
Commerce
National Oceanic and Atmospheric
Administration
National
Weather Service
National Data Buoy
Center
1007 Balch
Blvd.
Stennis Space Center, MS
39529
Feedback
Page last modified:
January 24, 2008

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