TITLE: CEOP Other ARM TWP Surface Meteorology and Radiation Data Set


CONTACT:


Raymond McCord
Building 1507
PO Box 2008, MS 6407
Oak Ridge, TN 37831-6407

Telephone: (865) 574-7827
Fax: (865) 574-4665

E-Mail: mccordra@ornl.gov


1.0  DATA SET OVERVIEW


This data set contains 30-minute resolution surface meteorology and
radiation data from the Coordinated Energy and Water cycle Observation Project (CEOP)
Reference Site operated by the Atmospheric Radiation Measurement (ARM) 
Program at its Tropical Western Pacific (TWP) facility.  This 
data set includes observations from three locations.  This data set 
covers the time period 1 October 2002 through 31 December 2009.  Further 
information about the ARM NSA site is available at the 
following URL: http://www.arm.gov

1.1  Station Locations

Site                Elev (m)  Latitude  Longitude
-------------------------------------------------
C1_Manus             4.0       -2.06    147.425
C2_Nauru             7.1       -0.521   166.916
C3_Darwin           29.9      -12.425   130.892

Note: The location of C3_Darwin changed on 19 May 2004.  Prior to that
date the location was -12.425 latitude, 130.891 longitude and 29.9 m 
elevation.  Starting 19 May and continuing to the end of EOP-4 it was
the location in the table above.

1.2 Time Period Covered by Data

All stations cover the complete EOP-3 and EOP-4 period (1 October 2002
to 31 December 2009).

1.3  Temporal Resolution

All data are 30-minute resolution.  See the instrumentation section for
further information.


2.0  INSTRUMENTATION DESCRIPTION

The ARM TWP surface meteorological measurements at the TWP sites are 
from their Surface Meteorology (SMET) system (see section 2.1).

The ARM TWP upwelling radiation measurements at the sites are from 
their GNDRAD system  (see section 2.2) and the ARM TWP downwelling
radiation measurements at the sites are from their SKYRAD system
(see section 2.3).

These stations provide observations of air temperature, dew point,
relative humidity, specific humidity, wind speed, wind direction, U wind
component, V wind component, station pressure, precipitation, incoming
longwave, incoming shortwave, outgoing longwave, outgoing shortwave,
net radiation, and skin temperature.

None of these stations provide observations of incoming PAR, outgoing
PAR, or snow depth.

2.1  SMET Sensors

For complete information on the SMET instrumentation see the
ARM SMET Handbook
and the updated version released in March 2008 here.  
Highlights are provided here.

2.1.1  Wind Speed at 10 m

A pair of propeller anemometers and wind vanes, R. M. Young Model 05106 
Wind Monitors

Precision: 0.01 m/s; Uncertainty: +/-1% for 2.5 to 30 m/s

The NIST calibration uncertainty is specified as +/-1% for wind speeds 
from the sensor threshold to 30 m/s. The conversion error is negligible. 
The schedule of routine maintenance and sensor verification is designed 
to eliminate any long-term stability error.

The sensor threshold is specified as 1 m/s. The following estimates of 
the range of underestimation caused by the threshold assume a normal 
distribution of wind speeds about the mean. When the true wind speed is 
1.0 m/s, the winds will be below the threshold 50% of the time. This 
will result in an underestimate of 0.5 m/s. When the true wind speed is 
1.5 m/s, assuming the standard deviation will be between 0.25 and 
1.00 m/s, the winds will be below the threshold between 2 and 31% of the 
time.  This will result in an underestimate between 0.02 and 0.23 m/s. 
When the true wind speed is 2.0 m/s with a range of standard deviations 
between 0.25 and 1.00 m/s, the winds will be below the threshold between 
0 and 16% of the time. This will result in an underestimate between 
0 and 0.12 m/s.

If the reported wind speed is 0.5 m/s, an underestimate of 0.5 is 
probable. This would bias the measurement by -0.5. If the reported wind 
speed is 1.0 m/s, an underestimate of 0.19 to 0.30 m/s is possible. If 
the reported wind speed is 1.5 m/s, an underestimate of 0.02 to 0.20 m/s 
is possible. If the reported wind speed is 2.0 m/s, an underestimate of 
0 to 0.10 m/s is possible.

The uncertainty range with 95% confidence is approximately:

+/- 1% 	                for a reported wind speed from 2.5 to 30.0 m/s
-0.12 to +0.02 m/s 	for a reported wind speed of 2.0 m/s
-0.22 to +0.00 m/s 	for a reported wind speed of 1.5 m/s
-0.31 to -0.20 m/s 	for a reported wind speed of 1.0 m/s
-0.51 to -0.49 m/s 	for a reported wind speed of 0.5 m/s

2.1.2 Wind Direction at 10 m

A pair of propeller anemometers and wind vanes, R. M. Young Model 05106
Wind Monitors

Precision: 0.1 deg; Uncertainty: +/-5 deg

The sensor accuracy is specified as +/-3 deg. The A-D conversion accuracy 
is equivalent to  0.7 deg over a temperature range of 0 to 40 deg C 
for a period of one year. I have estimated sensor alignment to true 
north to be accurate within +/-3 deg. The uncertainty with 95% confidence 
is, therefore, approximately +/-5 deg.

2.1.3  Air Temperature at 2 m

Platinum RTD and RH, Vaisala Model HMP35A Temperature and Relative 
Humidity Probe

Precision: 0.01 C; Uncertainty: +/-0.41 C

The accuracy of the temperature measurement is +/-0.1 C. The long-term 
stability is not known. The radiation error of the aspirated radiation 
shield is specified as +/-0.2 C rms. The uncertainty with 95% confidence 
of temperature sensors in this radiation shield is, therefore, about 
+/-0.41 C.

2.1.4  Humidity at 2 m

Platinum RTD and RH, Vaisala Model HMP35A Temperature and Relative 
Humidity Probe

Precision: 0.1% RH; Uncertainty: +/-2% RH (0% to 90% RH), +/-3% RH 
(90% to 100% RH)

The accuracy of the sensor is specified as +/-2% RH for 0 to 90% RH, 
and +/-3% RH for 90 to 100% RH. Errors considered in this accuracy are 
calibration uncertainty, repeatability, hysteresis, temperature 
dependence, and long-term stability over a period of one year. The A-D 
conversion accuracy is equivalent to +/-0.05% RH, which is negligible.

2.1.5 Barometric Pressure at 1 m

Digital barometer, Vaisala Model PTB201A

Precision: 0.01 kPa; Uncertainty: +/-0.035 kPa

The manufacturer's technical data contains an uncertainty analysis. 
Errors included in their analysis are linearity, hysteresis, calibration 
uncertainty, repeatability, temperature dependence, and long-term 
stability over a period of one year. Because the sensor has a digital 
output, no conversion error occurs in the data logger. The specified 
uncertainty with 95% confidence is +/-0.035 kPa. Note that the pressure 
behaves anomalously during rain events - even very mild ones.  Normally, 
the pressure undergoes a smooth semi-diurnal oscillation with little 
higher frequency variability. However, during and shortly after rain 
events, the pressure signal exhibits abrupt changes.

2.1.6 Precipitation

Optical precipitation gauge, Scientific Technology, Inc. Model 
ORG-115-DA Mini-Org

Precision: 0.1 mm/hr; Uncertainty: +/-0.1 mm/hr

The Optical raingauge has an uncertainty of +/-0.1 mm/hr. Values that 
fall between -0.1 mm/hr and +0.1 mm/hr should be considered 0 mm/hr. In 
other words, no rainfall is ocurring.

2.1.7 System Configuration

The SMET sensors are mounted on a 10-meter mast, except for the rain 
gauge.

The wind monitor propeller anemometers produce a magnetically controlled 
AC output whose frequencies are proportional to the wind speed. The Wind 
Monitor direction vanes drive potentiometers, which are part of 
resistance bridges.

Two Wind Monitors are mounted on a cross-arm at a height of 10 m. One is 
mounted slightly above the other in order to minimize interference. The 
higher wind monitor is designated sensor #1 and the lower wind monitor is 
designated sensor #2

The T-RH probe 4-lead, platinum resistance thermometer is part of a 
resistance bridge. The Vaisala RH circuitry produces a voltage that is 
proportional to the capacitance of a water vapor absorbing, thin polymer 
film. The T-RH probe is mounted in an R. M. Young Model 43408 Gill 
Aspirated Radiation Shield at a height of 2 m.

The barometric pressure sensor uses a silicon capacitive pressure sensor 
and is housed in a water-tight enclosure along with the data logger.

The optical precipitation gauge detects scintillation of an infrared beam 
caused by liquid water in the path. It is located near the tower.

The data logger measures each input once per second except for barometric 
pressure, which is measured once per minute, and logs 1-min averaged 
data. Vapor pressure is computed from the air temperature and relative 
humidity. The data logger produces 1-min averages, minimums, maximums, 
and standard deviations of wind speed, air temperature, relative 
humidity, and rain rate.  It also produces 1-min vector-averaged wind 
speed and direction, a 1-min standard deviation of the wind direction 
computed by an algorithm, 1-min averages and standard deviations of vapor 
pressure, a 1-min maximum wind gust speed, and a reading of the 
barometric pressure, internal temperature, and the external and internal 
supply voltages. The time reported for the 1-min statistics is the time 
of the last sample.

2.2 GNDRAD Sensors

For complete information on the GNDRAD instrumentation see the
ARM GNDRAD Handbook.  Highlights are provided here.

Upward Directed Longwave Radiation

The following radiometers manufactured by The Eppley Laboratory, Inc., are
used at each GNDRAD.

Measurement Radiometer  Mounting    Typical       Typical
	      Model    Arrangement  Responsivity  Calibration
                                    (uV/Wm-2)     Uncertainty*
---------------------------------------------------------------
Upwelling      PSP     Inverted w/o    9.0        +/-3.0% or
Shortwave              ventilation                10 Wm-2

Upwelling      PIR     Inverted w/o    4.0        +/-2% or
Longwave               ventilation                2 Wm-2

*Field measurement uncertainties are larger and include the uncertainties
associated with instrument calibration, installation, operation and
maintenance.

Additional information is available from http://www.eppleylab.com,
http://www.nrel.gov/srrl/, and http://rredc.nrel.gov.

The skin temperature is measured using an Infrared Temperature (IRT)
sensor (Heimann KT 19.85 Infrared Radiation Pyrometer)

2.3  SKYRAD Sensors

For complete information on the SKYRAD instrumentation see the
ARM SKYRAD Handbook.  Highlights are provided here.

Instrument     Description                             Wavelength
PIR2           Precision IR Radiometer, Pyrgeometer    4.0 to 50.0 um
PSP            Precision Spectral Pyranometer          0.285 to 2.8 um
NIP             Normal Incidence Pyheliometer          0.285 to 2.8 um


3.0  DATA COLLECTION AND PROCESSING


3.1  ARM Data Collection and Processing

For complete information on the SKYRAD instrumentation see the
ARM SKYRAD Handbook.

For complete information on the GNDRAD instrumentation see the
ARM GNDRAD Handbook.

For complete information on the SMET instrumentation see the
ARM SMET Handbook 
and the updated version released in March 2008 here.


3.2  NCAR/EOL Data Processing

The National Center for Atmospheric Research/Earth Observing Laboratory
(NCAR/EOL) converted the data from the raw format provided by ARM into 
the CEOP reference site data format agreed to by the CEOP Scientific 
Steering Committee.  This format is described in detail as part of the 
CEOP Reference Site Data Set Procedures Report which is available at the 
following URL:

http://www.eol.ucar.edu/projects/ceop/dm/documents/refdata_report

The SMET, GNDRAD and SKYRAD provide 1 minute measurements, the observations
at the 00 and 30 minute marks of every hour are included in the final
data set.

4.0  QUALITY CONTROL PROCEDURES


4.1  ARM Quality Control Procedures

Data are compared to upper and lower limits and flags are reported by 
the data logger. The flags are described in the netcdf header of each 
data file. No additional flags are applied during data ingest.

For complete information on the SKYRAD instrumentation see the
ARM SKYRAD Handbook.

For complete information on the GNDRAD instrumentation see the
ARM GNDRAD Handbook.

For complete information on the SMET instrumentation see the
ARM SMET Handbook
and the updated version released in March 2008 here.


4.2  NCAR/EOL Quality Control Procedures

NCAR/EOL converted the ARM QC flags into the CEOP QC flags in the 
following manner.  If a parameter failed one of the ARM QC checks it was 
flagged as Questionable/Dubious ("D") and if it failed two or more ARM 
QC checks it was flagged as Bad ("B").

Additionally, NCAR/EOL conducted two primary quality assurrance/control
procedures on the reference site data.  First the data has 
been evaluated by a detailed QA algorithm that verifies the format is 
correct, examines any QC flags, and conducts basic checks on data 
values.  Second, EOL conducts a manual inspection of time series 
plots of each parameter.


5.0  GAP FILLING PROCEDURES


No gap filling procedures were applied to these data by either
ARM or NCAR/EOL.


6.0  DATA REMARKS


6.1  Precipitation values less than 0.1 mm/hr

During normal operation, the sensor always puts out some voltage 
(background noise), even during clear sky conditions. The rain rate 
equation that is used to convert voltage to rain rate should only be 
applied to voltages equal to or above a certain fixed threshold. This 
threshold is different for each model(ORG-815 or ORG-115-DA mini-ORG). 
At values below the fixed threshold the equipment will report small 
values (some negative) at all times. Currently, the rain rate equation 
is used for all voltages reported by the sensor. The rain rates that 
correspond to voltages below the thresholds are between -0.1 mm/hr and 
+0.1 mm/hr. Therefore, such values should be considered by the data user 
to be 0 mm/hr. It is also possible that values between -0.15 mm/hr and 
-0.1 mm/hr may be reported as a result of very low voltages. These 
values should also be considered as 0 mm/hr. If values less than 
-0.15 mm/hr are reported then negative voltages are being used and this 
is an indication of a problem with the sensor. These values should be 
discarded. Any value equal to and above 0.1 mm/hr that are reported are 
good values since positive voltages above the thresholds are being 
reported and the rain rate equation is valid.


7.0  REFERENCE REQUIREMENTS


To support the continuation of this program, please include the
following 'credit line' in the acknowledgments of your
publication:

"Data were obtained from the Atmospheric Radiation Measurement
(ARM) Program sponsored by the U.S. Department of Energy, Office
of Science, Office of Biological and Environmental Research,
Environmental Sciences Division."


8.0  REFERENCES

For complete information on the SKYRAD instrumentation see the
ARM SKYRAD Handbook.

For complete information on the GNDRAD instrumentation see the
ARM GNDRAD Handbook.

For complete information on the SMET instrumentation see the
ARM SMET Handbook
and the updated version released in March 2008 here.