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: email@example.com 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.