ARM TR 008 7654 Bmet Handbook
User Manual: 7654
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ARM TR-034 Barrow Meteorology Station Handbook November 2004 M. T. Ritsche Work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research November 2004, ARM TR-034 Contents 1. 2. 3. 4. 5. 6. 7. General Overview ............................................................................................................................... 1 Contacts............................................................................................................................................... 1 Deployment Locations and History..................................................................................................... 2 Near-Real-Time Data Plots ................................................................................................................. 2 Data Description and Examples .......................................................................................................... 3 Data Quality ...................................................................................................................................... 10 Instrument Details ............................................................................................................................. 11 Tables 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. ............................................................................................................................................................. 2 NSA Met Tower.................................................................................................................................. 3 Present Weather Sensor....................................................................................................................... 4 Chilled Mirror Hygrometer ................................................................................................................. 5 Optical Rain Gauge ............................................................................................................................. 5 NSA Met Tower.................................................................................................................................. 5 Present Weather Sensor....................................................................................................................... 7 Chilled Mirror Hygrometer ................................................................................................................. 7 Optical Rain Gauge ............................................................................................................................. 7 NSA Met Tower.................................................................................................................................. 8 Present Weather Sensor....................................................................................................................... 8 Optical Rain Gauge ............................................................................................................................. 8 NSA Met Tower.................................................................................................................................. 9 Present Weather Sensor....................................................................................................................... 9 Chilled Mirror Hygrometer ................................................................................................................. 9 Optical Rain Gauge ............................................................................................................................. 9 iii November 2004, ARM TR-034 1. General Overview The Barrow meteorology station (BMET) uses mainly conventional in situ sensors mounted at four different heights on a 40 m tower to obtain profiles of wind speed, wind direction, air temperature, and humidity. It also obtains barometric pressure, visibility, and precipitation data. 2. Contacts 2.1 Mentor Michael Ritsche Argonne National Laboratory 9700 South Cass Avenue Argonne, IL 60439 Phone: 630-252-1554 Fax: 630-252-5498 E-mail: mtritsche@anl.gov 2.2 Instrument Developer Wind Speed and Direction, Temperature and Relative Humidity, Barometric Pressure, Present Weather Vaisala 100 Commerce Way Woburn, MA 01801-1068 Phone: 617-933-4500 Fax: 617-933-8029 Aspirated Radiation Shields R.M. Young Company 2801 Aero-Park Drive Traverse City, MI 49686 Phone: 616-946-3980 Fax: 616-946-4772 Chilled-Mirror Hygrometer Meteolabor AG Hofstrasse 92 CH-8620 Wetzikon Schweis Phone: (+41) 1 932 18 81 Fax: (+41) 1 932 32 49 Web page: www.meteolabor.ch 1 November 2004, ARM TR-034 Precipitation Scientific Technology, Inc. 205 Perry Parkway, Suite 14 Gaithsburg, MD 20877-2141 Phone: 301-948-6070 Fax: 301-948-4674 Computer Gateway2000 610 Gateway Drive P.O. Box 2000 North Sioux City, SD 57049-2000 Phone: 605-232-2000 Fax: 605-232-2023 RocketPort 485 Multport Board Control Corporation 900 Long Lake Road St. Paul, MN 55112 Phone: 612-631-7654 Fax: 612-631-8117 BridgeVIEW software National Instruments 6504 Bridge Point Parkway Austin, TX 78730-5039 Phone: 512-794-0100 Fax: 512-794-8411 3. Deployment Locations and History This one-of-a-kind system was installed at the NSA Barrow Alaska site in March 1998. In October 2003 the collection system and various sensors were replaced. See the Surface and Tower Meteorological Instrumentation at Barrow (METTWR4H) for the current data, sensors and measurement methods. Table 1. Location Date installed Date Removed Status 03/1998 N/A-changed changed NSA C2 4. Near-Real-Time Data Plots This section is not applicable to this instrument. 2 November 2004, ARM TR-034 5. Data Description and Examples This section is not applicable to this instrument. 5.1 5.1.1 Data File Contents Primary Variables and Expected Uncertainty The BMET station directly measures wind speed, wind direction, air temperature, and relative humidity at 2 m, 10 m, 20 m, and 40 m. Vector-averaged wind speeds, vector-averaged wind directions, dew points, and vapor pressures are computed from these primary measurements. Periodically, 2 m air and dew point temperatures are measured using a chilled-mirror hygrometer. Barometric pressure, visibility, and precipitation at the surface are also directly measured. Table 2. NSA Met Tower Quantity Variable Unit Barometric Pressure atmos_pressure hPa Mean Wind Speed wind_spd_mean m/s wind_spd_max m/s wind_spd_min m/s wind_spd_vec_avg m/s wind_dir_vec_avg deg wind_dir_sd deg wind_dir_max deg wind_dir_min deg temp_mean C temp_max C temp_mean C Maximum Wind Speed Minimum Wind Speed Vector-averaged Wind Speed Vector-averaged Wind Direction Std Dev of Wind Direction Maximum Wind Direction Minimum Wind Direction Mean Air Temperature or Hardware Error Maximum Air Temperature Minimum Air Temperature 3 Measurement Level Measurement Interval Resolution 4m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 1 min 0.01 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 1 min 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 November 2004, ARM TR-034 Table 2. (cont’d) Quantity Mean Relative Humidity Maximum Relative Humidity Minimum Relative Humidity Mean Dew Point Temperature Maximum Dew Point Temperature Minimum Dew Point Temperature Mean Vapor Pressure Maximum Vapor Pressure Minimum Vapor Pressure Variable Unit relh_mean % relh_max % relh_min % dew_pt_temp_mean C dew_pt_temp_max C dew_pt_temp_min C vap_pres_mean hPa vap_pres_max hPa vap_pres_min hPa Measurement Level 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m Measurement Interval Resolution 1 min 0.01 1 min 0.01 1 min 0.01 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 1 min 0.001 Table 3. Present Weather Sensor Quantity NWS Code One Minute Visibility Ten Minute Visibility One Minute PW code Ten Minute PW Code One Hour PW code Precipitation Rate Cumulative Liquid Water Equivalent Cumulative Snow Variable Unit Measurement Level Measurement Interval Resolution present_weather_sensor_ NWS_code N/A 3m 1 min N/A one_minute_visibility m 3m 1 min 1 ten_minute_visibility m 3m 1 min 1 one_minute_PW_code N/A 3m 1 min N/A ten_minute_PW_code N/A 3m 1 min N/A one_hour_PW_code N/A 3m 1 min N/A precip_rate mm/hr 3m 1 min 0.01 cumul_liq_water_equiv mm/hr 3m 1 min 0.01 cumul_snow mm/hr 3m 1 min 0.01 4 November 2004, ARM TR-034 Table 4. Chilled Mirror Hygrometer Variable Unit Measurement Level Measurement Interval Resolution air_temp C 2m 10 min 0.1 dew_pt_temp C 2m 10 min 0.01 relh % 2m 10 min 0.1 Quantity Air temperature Dew point temperature Relative humidity Table 5. Optical Rain Gauge Variable Unit Measurement Level Measurement Interval Resolution Uncertainty precip_NWS_code N/A 1m 1 min N/A N/A precip_rate mm/hr 1m 1 min 0.001 5% precip_daily_accum mm 1m 1440 min 0.001 10% Quantity NWS Code ORG Precipitation Rate Daily Accumulation 5.1.1.1 Definition of Uncertainty When the wind speed drops below the starting threshold for the cup anemometers or the wind vanes, the sensors will not respond properly. If the wind speed stays below the starting threshold, the sensors will not respond at all. During periods of rime ice, the air flow through the aspirated radiation shields will be modified. The air flow may be reduced and the temperature in the shield may be closer to that of the rime ice than that of the air. The humidity in the shield may also be affected. 5.1.2 Secondary/Underlying Variables This section is not applicable to this instrument. 5.1.3 Diagnostic Variables Table 6. NSA Met Tower Variable Barometric Pressure out of range error Barometric Pressure read timeout error PTB Serial Error Measurement Interval Measurement Level Min Max atmos_pressure_out_of_range_error 4m 800 1100 atmos_pressure_read_timeout_error 4m atmos_pressure_PTB_Serial_Error 4m 5 November 2004, ARM TR-034 Table 6. (cont’d) Variable Std Dev of Wind Speed Std Dev of Air Temperature Std Dev of Relative Humidity or Hardware Error Code Std Dev of Dew Point Temperature Std Dev of Vapor Pressure Wind Speed out of range error Wind Direction out of range error Air Temperature out of range error Relative Humidity out of range error Dew Point Temperature out of range error Vapor Pressure out of range error Internal Voltage out of range error Internal Temperature out of range error Air Temperature Hardware Error Dew Point Temperature Hardware Error Number of timeout readings of the met tower data by QLI Measurement Interval wind_spd_sd temp_sd relh_sd dew_pt_temp_sd vap_pres_sd wind_spd_out_of_range_error wind_dir_out_of_range_error temp_out_of_range_error relh_out_of_range_error dew_pt_temp_out_of_range_error vap_press_out_of_range_error internal_voltage_out_of_range internal_temp_out_of_range_error temp_hardware_error dew_pt_hardware_error read_timeout_count 6 Measurement Level 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m Min Max 0 100 0 360 -50 30 -2 104 -60 30 0.002 43 21.5 28.5 -50 100 N/A N/A N/A N/A N/A N/A November 2004, ARM TR-034 Table 7. Present Weather Sensor Variable One Minute Visibility out of range error Ten Minute Visibility out of range error One Minute PW code out of range error Ten Minute PW code out of range error One Hour PW code out of range error PWS Precipitation Rate out of range error Liquid Water Equivalent out of range error Cumulative Snow out of range error Present Weather Sensor Serial Error Present Weather Sensor Read Timeout Error Measurement Interval Min Max one_minute_vis_out_of_range_error 0 50000 ten_minute_vis_out_of_range_error 0 50000 one_min_pw_code_out_of_range_error 0 99 ten_min_pw_code_out_of_range_error 0 99 one_hour_pw_code_out_of_range_error 0 99 precip_rate_out_of_range_error_ 0 999 cumul_liq_water_equiv_out_of_range_error 0 999 cumul_snow_out_of_range_error 0 999 pws_serial_error N/A N/A pws_read_timeout_error N/A N/A Table 8. Chilled Mirror Hygrometer Quantity Air temperature out of range error Dew point temperature out of range error Relative Humidity out of range error Read timeout error Serial port read error Variable Measurement Interval Min Max air_temp_out_of_range_error 10 min unk unk dew_pt_temp_out_of_range_error 10 min unk unk relh_out_of_range_error 10 min unk unk read_timeout_error 10 min unk unk serial_read_error 10 min unk unk Table 9. Optical Rain Gauge Variable Measurement Interval Min Max Daily Accumulation out of range error precip_out_of_range_error 1 min 0 700 ORG No Data Error precip_no_data_error 1 min N/A N/A precip_read_timeout_error 1 min N/A N/A precip_serial_error 1 min N/A N/A Quantity ORG Read Timeout Error ORG Serial Error 7 November 2004, ARM TR-034 5.1.4 Data Quality Flags Data Quality flags were contained in the MetTWR, Mettiptwr, Optical Rain Gauge (ORG), Present Weather Sensor (PWS), and Snow Depth Sensor Data Object Design Changes for ARM netCDF file header descriptions. Contact the mentor if you need a copy. Table 10. NSA Met Tower Quantity Barometric Pressure Mean Wind Speed Vector-averaged Wind Direction Mean Air Temperature or Hardware Error Mean Relative Humidity Mean Dew Point Temperature Mean Vapor Pressure Variable qc_atmos_pressure qc_wind_spd_mean qc_wind_dir_vec_avg qc_temp_mean qc_relh_mean qc_dew_pt_temp qc_vap_pres_mean Measurement Level Measurement Interval Min Max Delta 4m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 2m, 10m, 20m, 40m 1 min 800 1100 10 1 min 0 100 20 1 min 0 360 90 1 min -60 30 10 1 min -2 104 30 1 min -60 30 10 1 min 0.002 43 10 Table 11. Present Weather Sensor Variable Measurement Interval Min Max Delta One Minute Visibility qc_one_minute_visibility 1 min 0 50000 5000 Ten Minute Visibility qc_ten_minute_visibility 1 min 0 50000 5000 One Minute PW Code qc_one_minute_PW_code 1 min 0 99 N/A Ten Minute PW Code qc_ten_minute_PW_code 1 min 0 99 N/A qc_one_hour_PW_code 1 min 0 99 N/A qc_precip_rate 1 min 0 999 100 qc_cumul_liq_water_equiv 1 min 0 999 100 qc_cumulative_snow 1 min 0 999 100 Quantity One Hour PW Code Precipitation Rate Cumulative Liquid Water Equivalent Cumulative Snow Table 12. Optical Rain Gauge Quantity ORG Precipitation Rate Variable Measurement Interval Min Max Delta qc_precip_rate 1 min 0 700 100 8 November 2004, ARM TR-034 5.1.5 Dimension Variables Table 13. NSA Met Tower Variable Measurement Interval Unit base_time 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX time_offset 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX lat 1 min degrees lon 1 min degrees alt 1 min meters above sea level Table 14. Present Weather Sensor Variable Measurement Interval Unit base_time 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX time_offset 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX Lat 1 min degrees Lon 1 min degrees Alt 1 min meters above sea level Table 15. Chilled Mirror Hygrometer Variable Measurement Interval Unit base_time 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX time_offset 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX lat 1 min degrees lon 1 min degrees alt 1 min meters above sea level Table 16. Optical Rain Gauge Variable Measurement Interval Unit base_time 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX time_offset 1 min seconds since YYYY-mm-dd XX:XX:XX X:XX lat 1 min degrees lon 1 min degrees alt 1 min meters above sea level 9 November 2004, ARM TR-034 5.2 Annotated Examples This section is not applicable to this instrument. 5.3 User Notes and Known Problems This section is not applicable to this instrument. 5.4 Frequently Asked Questions This section is not applicable to this instrument. 6. Data Quality 6.1 Data Quality Health and Status This section is not applicable to this instrument. 6.2 Data Reviews by Instrument Mentor Each data measurement value was compared to upper and lower limits by the data acquisition and processing program. If a single value obtained during the one-minute processing interval was outside of these limits, a flag was set and included in the data record for that minute. 6.3 Data Assessments by Site Scientist/Data Quality Office This section is not applicable to this instrument. 6.4 Value-Added Procedures and Quality Measurement Experiments Many of the scientific needs of the ARM Program are met through the analysis and processing of existing data products into "value-added" products or VAPs. Despite extensive instrumentation deployed at the ARM CART sites, there will always be quantities of interest that are either impractical or impossible to measure directly or routinely. Physical models using ARM instrument data as inputs are implemented as VAPs and can help fill some of the unmet measurement needs of the program. Conversely, ARM produces some VAPs not in order to fill unmet measurement needs, but instead to improve the quality of existing measurements. In addition, when more than one measurement is available, ARM also produces "best estimate" VAPs. A special class of VAP called a Quality Measurement Experiment (QME) does not output geophysical parameters of scientific interest. Rather, a QME adds value to the input datastreams by providing for continuous assessment of the quality of the input data based on internal consistency checks, comparisons between independent similar measurements, or comparisons between measurement with modeled results, and so forth. For more information, see the VAPs and QMEs web page. 10 November 2004, ARM TR-034 7. Instrument Details 7.1 7.1.1 Detailed Description List of Components Wind speed sensors: Vaisala WAA251 cup anemometers with heated cups and shafts are used to measure wind speed at each height. Vaisala quotes a starting threshold of about 0.5 m, a distance constant of 2.7 m, and a linear output with an accuracy of +/-0.17 m/s between 0.4 to 75 m/s. Wind direction sensors: Vaisala WAV251 wind vanes with heated shafts are used to measure wind direction at each height. Vaisala quotes a starting threshold of 0.4 m/s, a damping ratio of 0.14, an overshoot ratio of 0.65, and a delay distance of 0.4 m. Temperature and relative humidity sensors: Vaisala HMP35D or HMP45D Relative Humidity and Temperature Probes are used to measure air temperature and relative humidity at each height. They are mounted in R. M. Young 43408-2 Aspirated Radiation Shields. Vaisala quotes an accuracy of +/-2%RH (0% to 90%RH) and +/-3%RH (90% to 100% RH). Data converters: Vaisala QLI50 Sensor Collectors are used at each height to convert the wind speed, wind direction, temperature, and relative humidity sensor signals to digital data. DC power supplies: Vaisala WHP25 power supplies at each tower level power the instrumentation at that level. Chilled-mirror hygrometer: A Meteolabor AG VTP6 Ventilated Thermohygrometer is used to measure air and dew point temperatures at 2 m. It runs on a 10 minute cycle. Meteolabor AG quotes a resolution of 0.1 deg C resolution and an accuracy of +/- 0.15 deg C between -20 deg C and +50 deg C and +/-0.25 deg C between -65 deg C and -20 deg C. Precipitation sensor: A Scientific Technology, Inc. ORG-815-DR optical precipitation sensor is used to obtain the accumulation of liquid or frozen precipitation. ScTi quotes a resolution of 0.001 mm and an accuracy of +/-5% for rain and +/-10% for snow. Present weather sensor: A Vaisala FD12P Present Weather Sensor produces visibility and precipitation data. It also produces NWS and WMO weather codes. Vaisala quotes the visibility accuracy to be +/10% between 10 and 10,000 meters and +/-20% for 10,000 to 50,000 meters and a precipitation accuracy of +/-30%. Barometric pressure sensor: A Vaisala PTB201A Digital Barometer is used to measure the station barometric pressure. The barometer has a resolution of 0.1 hPa and an accuracy of 0.25 hPa. Data acquisition and processing system: A Gateway2000 G6-300 computer is used to acquire and process the data. 11 November 2004, ARM TR-034 7.1.2 System Configuration and Measurement Methods A set of sensors for measuring wind speed, wind direction, air temperature, and relative humidity and a Sensor Collector which converts the signals from the sensors into digital data are deployed on each of 4 booms mounted on the 40 m tower. A chilled-mirror hygrometer is mounted at 2 m near the 2 m boom. An optical precipitation sensor is mounted on an arm at the base of the tower. A Present Weather Sensor and a digital barometer are located nearby. Wind speed at 2, 10, 20 and 40 m The cup anemometers use a photo-chopper to produce a 10 Hz per m/s signal. The Sensor Collectors determine the frequency by obtaining the average period between pulses and convert them to wind speeds. Both the cups and the shafts of these sensors are heated in order to prevent ice buildup from affecting the accuracies of the measurements. One minute means, vector-averages, and standard deviations are reported with a precision of 0.001 m/s but have a resolution of only 0.02 m/s. Minima and maxima are reported with a precision of 0.1 m/s Wind direction at 2, 10, 20 and 40 m The wind vanes use an optically detected GRAY code disk with a 5.6 deg resolution. The Sensor Collectors convert the GRAY code into a binary value. The shafts of these sensors are heated in order to prevent ice buildup from affecting the accuracies of the measurements. Vector-averages and standard deviations are reported with a precision of 0.001 deg but have a resolution of only 0.1 deg. Minima and maxima are reported with 1 deg precision. Air temperature at 2, 10, 20 and 40 m The air temperature sensors, 4-wire 100 ohm platinum resistance thermometers, are included in the same probe as the relative humidity sensors. The probes are mounted in aspirated radiation shields to minimize radiation and self-heating errors. The Sensor Collectors supply a 1.2 mA constant-current excitation and measure the voltages across the sensors. They then compute the temperatures from the voltages. Means and standard deviations are reported with a precision of 0.001 C. Minima and maxima are reported with a precision of 0.01 C. Relative humidity at 2, 10, 20 and 40 m The relative humidity probes use Vaisala HUMICAP sensors and associated electronics to produce a 0 to 1 V output corresponding to an RH of 0 to 100%. The Sensor Collectors use A/D converters to measure the voltages and convert them to % RH. They also compute the Dew Points from the air temperatures and relative humidities. Means and standard deviations of relative humidity are reported with a precision of 0.001% RH but have resolution of only 0.1% RH. Minima and maxima are reported with a precision of 0.1% RH. 12 November 2004, ARM TR-034 Air and dew point temperatures at 2 m The Meteolabor AG VTP6 Ventilated Thermohygrometer uses a chilled-mirror hygrometer to measure the dew point temperature and a thermocouple to measure the air temperature. The hygrometer cycle incorporates a heater, a mirror cleaning feature, and automatic differentiation between ice and water films on the mirror. It makes 10 measurements within a 40 second period every 10 minutes and transmits averaged values. The data acquisition system obtains the past hour's readings a few minutes after the hour and writes the data to a separate file. Optical precipitation at the base of the tower The optical precipitation sensor measures rain or snow by detecting scintillation of a coherent infrared light beam. The sensor uses automatic gain control to eliminate the effects of source power drift or dirty optics. It reports precipitation as a digital (RS-232) output with a 0.001 mm precision. Visibility and Present Weather The Present Weather Sensor is a microprocessor controlled, intelligent sensor that uses a forward scatter visibility meter, a capacitive rain detector, and a platinum resistance thermometer to measure visibility and amount and type of precipitation. By monitoring the LED transmitted light intensity, the sensor compensates for temperature and aging effects. It has a digital (RS-232) output. Visibilities are reported in meters, precipitation in mm/hr, liquid water equivalence in mm, and total snow in mm. Barometric pressure The barometer produces a digital output from measurements of a silcon capacitive absolute pressure sensor. The sensor is located next to the computer in the shelter but has a port to the outside. It reports atmospheric pressure with a 0.1 hPa resolution. Data acquisition and processing National Instruments' BridgeVIEW, a superset of LabVIEW, is used on a Pentium II computer operating under WindowsNT4.0 to acquire and process the data. The Sensor Collectors, the optical precipitation sensor, the barometer, and the Present Weather Sensor are all digital output devices. The computer polls the Sensor Collectors every 2 seconds and computes means, standard deviations, minima, and maxima over periods of 1-minute duration. It also computes vapor pressures and vector-averaged winds. Once a minute it polls the barometer, the precipitation sensor, and the Present Weather Sensor. Once an hour it polls the chilled-mirror hygrometer. All incoming data are compared to limits and flags are set if any are outside those limits. 7.1.3 Specifications The specifications are given under List of Components, Section 7.1.1., and are further discussed under System Configuration and Measurement Methods, Section 7.1.2., above. 13 November 2004, ARM TR-034 7.2 Theory of Operation Each of the primary measurements of wind speed, wind direction, air temperature, relative humidity, barometric pressure, and rate of rainfall are intended to represent self-standing data streams that can be used independently or in combinations. The theory of operation of each of these sensors is similar to that for sensors typically used in other conventional surface meteorological stations. Some details can be found under Description of System Configuration and Measurement Methods but further, greatly detailed description of theory of operation is not considered necessary for effective use of the data for these rather common types of measurements. The instrument mentor or the manufacturers can be contacted for further information. 7.3 7.3.1 Calibration Theory The BMET is not calibrated as a system. The sensors along with the Sensor Collectors and the instruments are calibrated separately. The system was installed using components that had a current calibration. The sensor, Sensor Collector, and instrument calibrations are checked in the field by comparison to calibrated references. Any unit that fails a field check is returned to the manufacturer for recalibration. Wind speed calibrations are checked by rotating the anemometer shafts at a series of fixed rpm's using an R. M. Young Model 18810 Anemometer Drive. The reported wind speeds are compared to a table of expected values and tolerances. If the reported wind speeds are outside the tolerances for any rate of rotation, the sensor is replaced by one with a current calibration. Wind direction calibrations are checked by using a vane angle fixture, R. M. Young Model 18212, to position the vane at a series of angles. The reported wind directions are compared to the expected values. If any direction is in error by more than 5 degrees, the sensor is replaced by one with a current calibration. Air temperature and relative humidity calibrations are checked by comparison with the Meteolabor AG Ventilated Thermohygrometer. If the reported temperature and relative humidity vary by more than the sensor uncertainty from the reference, the probe is replaced by one with a current calibration. Barometric pressure calibration is checked by comparison with a reference Vaisala PA-11 Barometer. If the reported pressure varies by more than the sensor uncertainty from the reference, the sensor is replaced by one with a current calibration. The Present Weather Sensor is check calibrated following the manufacturer's recommendation. 7.3.2 Procedures This section is not applicable to this instrument. 14 November 2004, ARM TR-034 7.3.3 History All equipment were calibrated at the manufacturers prior to installation. A field check calibration on the instruments was made on 18 SEP 1999. All were within tolerances. All wind speed, wind direction, and temperature/humidity sensors were replaced and a field calibration check on the instruments were made on 9-13 OCT 2001. All were within tolerances. On September 18, 2002, the 20m wind speed sensor was replaced. The heating mechanism had failed causing the sensor to accumulate ice. 7.4 7.4.1 Operation and Maintenance User Manual This section is not applicable to this instrument. 7.4.2 Routine and Corrective Maintenance Documentation This section is not applicable to this instrument. 7.4.3 Software Documentation ARM netCDF file header descriptions were found in the MetTWR, Mettiptwr, Optical Rain Gage (ORG), Present Weather Sensor (PWS), and Snow Depth Sensor Data Object Design files. Contact the mentor to request a copy. 7.4.4 Additional Documentation This section is not applicable to this instrument. 7.5 Glossary See the ARM Glossary. 7.6 Acronyms See the ARM Acronyms and Abbreviations. 7.7 Citable References None 15
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