TITLE: CEOP CPPA ARM SGP 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)
Global Energy and Water Cycle Experiment (GEWEX) Climate Prediction 
Program for the Americas (CPPA) Reference Site operated by the Atmospheric Radiation
Measurement (ARM) Program at its Southern Great Plains (SGP) facility
in Kansas and Oklahoma.  This data set includes surface meteorological
observations from 14 locations and radiation data from 21 locations and
skin temperature from 1 location.  This data set covers the time period 
1 October 2002 through 31 December 2009.  Further information about the 
ARM SGP site is available at the following URL: 
http://www.arm.gov

1.1  Station Locations

Site          State   Elev (m)  Latitude  Longitude   Surface Type
--------------------------------------------------------------------------------
C1_Lamont      OK      318     36.605 N   97.485 W   Pasture
E1_Larned      KS      632     38.202 N   99.316 W   Wheat
E2_Hillsboro   KS      450     38.306 N   97.301 W   Grass
E3_Le_Roy      KS      338     38.201 N   95.597 W   Wheat and Soybeans (rotated)
E4_Plevna      KS      513     37.953 N   98.329 W   Rangeland (ungrazed)
E5_Halstead    KS      440     38.114 N   97.513 W   Wheat
E6_Towanda     KS      409     37.842 N   97.020 W   Alfalfa
E7_Elk_Falls   KS      283     37.383 N   96.180 W   Pasture
E8_Coldwater   KS      664     37.333 N   99.309 W   Rangeland (grazed)
E9_Ashton      KS      386     37.133 N   97.266 W   Pasture
E10_Tyro       KS      248     37.068 N   95.788 W   Alfalfa
E11_Byron      OK      360     36.881 N   98.285 W   Alfalfa
E12_Pawhuska   OK      331     36.841 N   96.427 W   Native Prairie
E13_Lamont     OK      318     36.605 N   97.485 W   Pasture and Wheat
E15_Ringwood   OK      418     36.431 N   98.284 W   Pasture
E16_Vici       OK      602     36.061 N   99.134 W   Wheat
E18_Morris     OK      217     35.687 N   95.856 W   Pasture (ungrazed)
E19_El_Reno    OK      421     35.557 N   98.017 W   Pasture (ungrazed)
E20_Meeker     OK      309     35.564 N   96.988 W   Pasture
E21_Okmulgee   OK      240     35.615 N   96.065 W   Forest
E22_Cordell    OK      465     35.354 N   98.977 W   Rangeland (grazed)
E24_Cyril      OK      409     34.883 N   98.205 W   Wheat (gypsum hill)
E27_Earlsboro  OK      300     35.269 N   96.740 W   Pasture

Note:  E19 has a slightly different location from the start of collection through
6 May 2003 (35.549 N and 98.020 W).  From 7 May 2003 to the end of collection
the location is as above.

Note: C1 has a slightly different location from the start of collection through
7 May 2003 (36.606 N and 97.485 W and 324 m).  From 7 May 2003 to the end of collection
the location is as above.

1.2 Time Period Covered by Data

All stations cover the complete time period (1 October 2002 to 31 December 2009)
except as follows:

E1 ended observations on 14 October 2009.
E2 ended observations on 20 October 2009.
E3 ended observations on 28 October 2009.
E5 ended observations on 2 November 2009.
E8 ended observations on 10 November 2009.
E18 ended observations on 17 November 2009.
E22 ended observations on 1 December 2009.
E24 ended observations on 14 November 2009.
E27 started observations on 7 May 2003 and ended them on 4 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 SGP surface meteorological measurements are from their 
Surface Meteorological Observation System (SMOS; see section 2.1) and 
the radiation measurements are from their Solar and Infrared Radiation 
System (SIRS; see section 2.2).  The ARM SGP skin temperature 
measurements are from their Infrared Temperature (IRT; see section 2.3).

The following stations provide both surface meteorological (air
temperature, dew point, relative humidity, specific humidity, station
pressure, wind speed, wind direction, U wind component, V wind
component and precipitation) and radiation (incoming longwave, incoming
shortwave, outgoing longwave, outgoing shortwave, and net radiation)
observations:

E1, E3, E4, E5, E6, E7, E8, E9, E11, E13, E15, E20, E21, E24, E27.

The following stations provide only radiation (incoming longwave,
incoming shortwave, outgoing longwave, outgoing shortwave, and net
radiation) observations:

C1, E2, E10, E12, E16, E18, E19, E22.

The C1 station also provides skin temperature observations.

No stations provide measurements of incoming PAR, outgoing PAR,
or snow depth.

2.1  SMOS Sensors

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

2.1.1  Wind Speed

Make and Model

Propellor anemometer and wind vane, R. M. Young Model 05103 Wind Monitor

Precision and Uncertainty

Wind speed at 10 m, 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

Make and Model

Propellor anemometer and wind vane, R. M. Young Model 05103 Wind Monitor

Precision and Uncertainty

Wind direction at 10 m, 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

Make and Model

Thermistor and Vaisala RH, Campbell Scientific Model HMP35C Temperature and 
Relative Humidity Probe

Precision and Uncertainty

Air temperature at 2 m, Precision: 0.01 C; Uncertainty: a function of wind 
speed 

The accuracy of the temperature measurement is specified as +/-0.4 C. 
Included in this accuracy are sensor interchangeability, bridge resistor 
precision, and polynomial curve fitting errors. The long-term stability is 
not known. The radiation error of the naturally aspirated multi-plate 
radiation shield used for all stations, except for the central facilities 
SMOS, is specified as +/-0.4 C rms at 3 m/s, +/-0.7 C rms at 2 m/s, and 
+/-1.5 C rms at 1 m/s.

The uncertainty with 95% confidence of temperature sensors in naturally 
aspirated radiation shields is approximately:

+/-0.45 C	when the wind speed is 6 m/s or greater
+/-0.89 C 	when the wind speed is 3 m/s
+/-1.46 C 	when the wind speed is 2 m/s
+/-3.07 C 	when the wind speed is 1 m/s

The radiation error of the aspirated radiation shield used at the Central 
Facility is specified as +/- 0.2 C rms. The uncertainty with 95% confidence 
of temperature sensors in this radiation shield is, therefore, +/- 0.57 C.

2.1.4  Humidity

Make and Model

Thermistor and Vaisala RH, Campbell Scientific Model HMP35C Temperature and
Relative Humidity Probe

Precision and Uncertainty

Relative humidity at 2 m, Precision: 0.1% RH; Uncertainty: +/-2.06% RH 
(0% to 90% RH), +/-3.04% 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 +/-0.5% RH.

The uncertainty with at least 95% confidence is, therefore,

+/-2.06 % RH, 0 to 90 % RH
+/-3.04 % RH, 90 to 100 % RH

2.1.5 Barometric Pressure

Make and Model

Digital barometer, Vaisala Model PTB201A

Precision and Uncertainty

Barometric pressure at 1 m, 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 Campbell data logger.

The specified uncertainty with 95% confidence is +/-0.035 kPa.

2.1.6  Precipitation

Make and Model

Electrically heated, tipping bucket precipitation gauge, Novalynx Model 
260-2500E-12 Rain/Snow Gage

Precision and Uncertainty

Precipitation, Precision: 0.254 mm; Uncertainty: +/-0.254 mm (unknown 
during strong winds and for snow)

The tipping-bucket rain gauge produces a pulse output. The data logger 
counts the pulses for the period of integration. The uncertainty is, 
therefore, a minimum of one full bucket or 0.254 mm. For rain rates less 
than 75 mm per hour with light to moderate winds, the collection 
efficiency of the gauge is 99 to 100%. During heavy rain or strong, gusty 
winds, the collection efficiency is reduced. Manufacturers have not 
attempted to specify accuracies for these conditions.

Although Alter shields are used to increase the efficiency of snow 
collection, the efficiency of collection is variable and usually well 
below 100%. Furthermore, the heater does not melt snow at temperatures 
below -10 deg C. Thus the data user should use the water-equivalent 
estimates for snowfall with a great deal of skepticism. At best, the 
readings are only a rough indicator that snow occurred, for temperatures 
above -10 C. If snow occurred at -10 C or below and the temperature 
increased to above -10 C hours later, then some melting would occur and 
an incorrect time of precipitation would be reported.

2.1.7  SMOS E21 Station Configuration

The instrument heights mentioned above are for all SMOS stations
except E21 in Okmulgee, OK.  E21 uses the same instrumentation but
since this SMOS is in a forrested site, the sensors are mounted on a 20 m 
tower which extends above the top of the forest canopy.  During the summer 
of 1999 the canopy height was estimated to be 47 feet or 14.3 m. The air 
temperature and relative humidity probe is mounted at 19.25 m or approximately 
4.95 m above the average canopy height facing Northeast. The wind speed and 
direction sensor is mounted at 18 m or approximately 3.7 m above the average 
canopy height on a boom 15ft out from the tower facing West.  The barometric 
pressure sensor is mounted at 19 m or approximately 4.7 m above the average 
canopy height. 

2.2 SIRS Sensors

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

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

                                         Typical        Typical
              Radiometer  Mounting       Responsivity   Calibration
Measurement   Model       Arrangement    (uV/Wm-2)      Uncertainty*
-------------------------------------------------------------------
Downwelling               Unshaded &                    +/- 3.0% or
Shortwave     PSP         Ventilated     9.0            10 Wm-2

Downwelling               Shaded &                      +/- 2% or
Longwave      PIR         Ventilated     4.0            2 Wm-2

Upwelling                 Inverted w/o                  +/- 3.0% or
Shortwave     PSP         ventilation    9.0            10 Wm-2

Upwelling                 Inverted w/o                  +/- 2% or
Longwave      PIR         ventilation    4.0            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.nrel.gov/srrl/.

DOWNWELLING SHORTWAVE (0.3 to 3.0 micrometers)

1. Direct Normal (beam) irradiance measured by a pyrheliometer with a 
5.7 degree field of view.

2. Diffuse Horizontal (sky) irradiance measured by a shaded and ventilated 
pyranometer with a hemispherical field of view, but blocked from the 
direct normal irradiance by a tracking ball.

3. Total Hemispheric (global) irradiance measured by an unshaded and 
ventilated pyranometer.

DOWNWELLING LONGWAVE (4.0 to 50 micrometers)

4. Total Hemispheric (atmospheric) irradiance measured by a shaded and 
ventilated pyrgeometer with a hemispheric field of view.

UPWELLING SHORTWAVE (0.3 to 3.0 micrometers)

5. Reflected irradiance measured by an inverted pyranometer with a 
hemispheric field of view.

UPWELLING LONGWAVE (4.0 to 50 micrometers)

6. Irradiance measured by an inverted pyrgeometer with a hemispheric 
field of view.

2.3  IRT Sensors

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

The IRT is located 10 m above the ground surface.

List of Components

Heimann KT 19.85 Infrared Radiation Pyrometer
Heimann T14 Power Supply
Environmental enclosure

Additional information on the IRT is available from ARM:

http://www.arm.gov/instruments/static/irt.stm


3.0  DATA COLLECTION AND PROCESSING


3.1  ARM Data Collection and Processing

SIRS

The data acquisition system is a Campbell Scientific, Inc. Model CR10X-1M 
with AM416 Multiplexer, 4 Mb memory card, and modem.  These components 
are inside a weather-resistant enclosure mounted above ground. The system 
is designed to operate over the full range of environmental conditions 
anticipated for the network of SIRS stations (see 
http://www.campbellsci.com for 
detailed measurement and environmental specifications).

The system is programmed to sample ten inputs listed below every 2-seconds 
and output the average, standard deviation, minimum, and maximum values of 
the six geophysical elements, described above, at the end of each minute. 
Appended to each 1-minute data output record are the instantaneous values 
sampled at 20 seconds, 40 seconds, and 60 seconds within the 1-minute 
interval. These "instantaneous" data actually require 0.272 milliseconds 
to complete the analog to digital conversion of each measurement.  
Additionally, at 23:59:02 each day, the instrument serial numbers and 
calibration factors used by the data logger program are appended to the 
last record of the day. The system is designed to store up to two weeks 
of measured data and statistics, but the data are generally collected by 
telephone modem every 3-hours. Data stored on the 4 Mb memory card at 
each station are physically removed as part of the routine SIRS 
maintenance every two weeks and made available to the SGP Data System.

Measurements collected by the CR10X-1M logger are listed below with a 
sample data record for reference. All data files are reformatted in 
NETcdf for distribution.

3.2  UCAR/JOSS Data Processing

The University Corporation for Atmospheric Research/Joint Offfice for
Science Support (UCAR/JOSS) converted the data from the raw format
provided by ARM into the CEOP EOP-3 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.joss.ucar.edu/ghp/ceopdm/refdata_report/ceop_sfc_met_format.html

The SMOS and SIRS instruments provide 1 minute observations, the 
observations at 00 and 30 minutes of each hour are included in
this data set.

UCAR/JOSS also derived the dew point, specific humidity, and U and
V wind components utilizing the equations provided in the same
report.


4.0  QUALITY CONTROL PROCEDURES


4.1  ARM Quality Control Procedures

For complete information on the ARM QC procedures see the
ARM
SMOS Handbook, the ARM
SIRS Handbook, or the ARM
IRT Handbook.  Highlights are provided here.

All SMOS data are checked for values outside the range of sensor calibration 
or expected values.  No delta checks are made.

Each qcmin is the decimal value of the binary string of bits set to 1 when 
the respective value is below the threshold.  Similarly, each qcmax is the 
decimal value of the binary string of bits set to 1 when the respective 
value is above the threshold. Thus, if the nth bit is set, then 2**(n-1) is 
added to the value of qcmin or qcmax.

Wind speed:
Minimum: Obviously, wind speed cannot be less than 0.
Maximum: Values above 45 meters per second are outside the range of the 
         sensor calibration.

Wind direction:
Minimum: 0 degrees by definition
Maximum: 360 degrees by definition.

Air Temperature:
Minimum: Values below -40 C are outside the range of the sensor calibration.
Maximum: Values above 50 C are outside the range of the sensor calibration.

Relative humidity
Minimum: Values below -2% RH are outside the range of the sensor 
         calibration and uncertainty.
Maximum: Values above 104% RH are outside the range of the sensor 
         calibration and uncertainty.

Barometric pressure
Minimum: Values below 80 kPa are outside the range of the sensor calibration.
Maximum: Values above 110 kPa are outside the range of the sensor calibration.

Precipitation
Minimum: Values less than 0 are not possible.
Maximum: Values above 150 mm per half-hour exceed the ability of the 
         tipping bucket to measure accurately.

4.2  UCAR/JOSS Quality Control Procedures

UCAR/JOSS 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, ARM issues Data
Quality Reports (DQRs) anytime problems are noticed within the data stream
(e.g. failing instruments, calibration periods, etc).  UCAR/JOSS has
examined the DQRs issued by ARM over this time period (over 140 DQRs were
issued) and determined when the parameters included within this data set
may have been impacted and flagged the data either "D" or "B" based on the
description of the problem included in the DQR.  The ARM DQR's are provided
as part of the data set:

DQR_SGP_IRT_200312_200412.html
DQR_SGP_SIRS_200201_200212.html
DQR_SGP_SIRS_200301_200309.html
DQR_SGP_SIRS_200310_200412_1.html
DQR_SGP_SIRS_200310_200412_2.html
DQR_SGP_SMOS_200201_200212.html
DQR_SGP_SMOS_200301_200309.html
DQR_SGP_SMOS_200310_200403.html
DQR_SGP_SMOS_200404_200412.html

Additionally, UCAR/JOSS 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, JOSS conducts a manual inspection of time series 
plots of each parameter.  Additional flags were applied during this
step.


5.0  GAP FILLING PROCEDURES


No gap filling procedures were applied to these data by either
ARM or UCAR/JOSS.


6.0  DATA REMARKS


6.1  E21 Precipitation Questionable

Since the height of the tower at E21 extends above the forest canopy it 
has become a favorite roosting area for turkey vultures.  The birds 
roosting on the tower has caused considerable amounts of bird droppings 
on the equipment, tower & sensors. The precipitation gage is frequently 
clogged with bird droppings during the time period that the vultures are 
in the area. The turkey vultures are migratory but are generally in the 
area from early April through sometime in November. Precipitation data 
during these times should be investigated closely to determine if the 
precipitation gage data is consistent with other nearby sites.  Typically 
when the raingage is clogged a stairstep pattern in the data can be noticed.


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

Further information on ARM SGP SMOS instrumentation (including calibration
and maintenance and references) can be found at the 
ARM SMOS
Handbook.

Further information on ARM SGP SIRS instrumentation (including QC, calibration,
maintenance, theory of operation, and references) can be found at the
ARM SIRS
Handbook.

Further information on ARM SGP IRT instrumentation (including calibration
and maintenance and references) can be found at the ARM IRT web page:
ARM IRT
Handbook.