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Measurement Descriptions and Units
Real Time files generally contain the last 45 days of "Realtime" data - data that went through automated quality checks and were distributed as soon as they were received. Historical files have gone through post-processing analysis and represent the data sent to the archive centers. The formats for both are generally the same, with the major difference being the treatment of missing data. Missing data in the Realtime files are denoted by "MM" while a variable number of 9's are used to denote missing data in the Historical files, depending on the data type (for example: 999.0 99.0).
General
Units: 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.
Time: Station pages show current observations in station local time by default, but can be changed by the viewer to UTC (formely GMT). Both Realtime and Historical files show times in UTC only. See the Acquisition Time help topic for a more detailed description of observation times. For more information on the times in the files, see the changes page at http://www.ndbc.noaa.gov/mods.shtml.
Staion ID: Five-digit WMO Station Identifier, used since 1976. ID's can be reassigned to future deployments within the same 1 degree square.
Formats: Data are classified according to the following groups. The header lines are shown at the beginning of group. Note that in the Realtime files, non-data lines begin with "#". Such lines should be treated as comment lines.
Standard Meteorological Data
#YY MM DD hh mm WDIR WSPD GST WVHT DPD APD MWD PRES ATMP WTMP DEWP VIS PTDY TIDE
#yr mo dy hr mn degT m/s m/s m sec sec degT hPa degC degC degC nmi hPa ft
2007 04 15 13 50 120 4.0 6.0 0.4 3 MM MM 1023.4 20.6 22.5 10.8 MM +1.7 MM
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 |
The direction from which the waves at the dominant period (DPD) are
coming. The units are degrees from true North, increasing clockwise, with
North as 0 (zero) degrees and East as 90 degrees.
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). (
labeled BAR in Historical files) |
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 (nautica miles). Note that buoy stations are limited to reports from 0 to 1.6 nmi. |
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. (not in Historical files) |
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.
|
WSPD10 |
The estimation of Wind Speed (WSPD) measurement raised or lowered to a height
of 10 meters. NDBC uses the method of Liu et al., 1979: Bulk parameterization
of air-sea exchanges in heat and water vapor including molecular constraints at
the interface, Journal of Atmospheric Science, 36, pp. 1722-1735. |
WSPD20 |
The estimation of Wind Speed (WSPD) measurement raised or lowered to a height
of 20 meters. NDBC uses the method of Liu et al., 1979: Bulk parameterization
of air-sea exchanges in heat and water vapor including molecular constraints at
the interface, Journal of Atmospheric Science, 36, pp. 1722-1735. |
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 occurred (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 occurred (hour and minute). |
Continuous Winds
#YY MM DD hh mm WDIR WSPD GDR GST GTIME
#yr mo dy hr mn degT m/s degT m/s hhmm
2007 03 05 06 20 314 8.0 320 10.0 0604
WDIR |
Ten-minute average wind direction measurements in degrees clockwise
from true North. (DIR in Historical files) |
WSPD |
Ten-minute average wind speed values in m/s. (SPD in Historical files) |
GDR |
Direction, in degrees clockwise from true North, of the GST,
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 (Realtime data files only)
#YY MM DD hh mm WVHT SwH SwP WWH WWP SwD WWD STEEPNESS APD MWD
#yr mo dy hr mn m m sec m sec - degT - sec degT
2007 03 05 05 32 1.5 0.5 11.0 1.5 9.0 W MM AVERAGE MM -99
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. |
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. |
SwD |
The direction from which the swell waves at the swell wave
period (SWPD) are coming. The units are degrees from true North,
increasing clockwise, with North as 0 (zero) degrees and East as 90
degrees. |
WWD |
The direction from which the wind waves at the wind wave period (WWPD)
are coming. The units are degrees from true North, increasing clockwise,
with North as 0 (zero) degrees and East as 90 degrees. |
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 |
The direction from which the waves at the dominant period (DPD) are
coming. The units are degrees from true North, increasing clockwise, with
North as 0 (zero) degrees and East as 90 degrees.
See the Wave Measurements section. |
Spectral Wave Data
#YY MM DD hh mm Sep_Freq < spec_1 (freq_1) spec_2 (freq_2) spec_3 (freq_3) ... >
2007 03 05 06 30 0.143 0.000 (0.033) 0.000 (0.037) 0.000 (0.043) 0.000 (0.048) ...>
#YY MM DD hh mm alpha1_1 (freq_1) alpha1_2 (freq_2) alpha1_3 (freq_3) ... >
2007 03 05 06 30 999.0 (0.033) 999.0 (0.037) 999.0 (0.043) 999.0 (0.048) ...
Sep_Freq |
The Separation Frequency is the frequency that separates wind waves (WWH, WWP, WWD)
from swell waves (SWH, SWP,SWD). NDBC inserts the value 9.999 if Sep_Freq is missing. |
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.})
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Notes:
- 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.
- D(f,A) can take on negative values because of the trigonometric sine and cosine functions. There are several approaches to prevent or deal with the negative values. For more information and discussion of some approaches see: Use of advanced directional wave spectra analysis methods, M. D. Earle, K. E. Steele, and D. W. C. Wang, Ocean Engineering, Volume 26, Issue 12, December 1999, Pages 1421-1434.
- ALPHA2 has ambiguous results in using the arctangent function with the Fourier Coefficients,b 2 ,a 2 . When necessary, NDBC adds 180 degrees to ALPHA2 in order to minimize the difference between ALPHA 1 and ALPHA2.
|
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
#YY MM DD hh mm DEPTH OTMP COND SAL O2% O2PPM CLCON TURB PH EH
#yr mo dy hr mn m degC mS/cm psu % ppm ug/l FTU - mv
2007 04 27 11 00 2 25.13 55.18 36.45 33.1 2.21 0.06 MM 0.00 98.28
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 (Tsunameters) 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. |
tt = Tsunami Trigger Time, see the Tsunami Detection Algorithm
ts = data Time Stamp(s)
|
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 |
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