10/22/20121Instruments/Measurements• Measuring– Errors, Calibration, Sensitivity, Range, etc• Temperature– Aspiration/Shielding– Thermistors, thermocouples, mercury•Wind– Exposure– Cups, sonic anemometers• Radiation– Quantum vs Energy– Leaf Area Index• Trace Gases– Infrared absorption10/22/2012 ESPM 129 BiometeorologyESPM 129 Biometeorology 2Attributes of Measurements• Precision• Accuracy– Random and Systematic Errors• Sensitivity• Stability• Time Response• Exposure• Representativeness– Aspiration– Sheltering, e.g. Sun, Wind and Rain • Calibration10/22/20122ESPM 129 Biometeorology 3Accuracy and PrecisionESPM 129 Biometeorology 4LI 6262irg3-1079Reference Temperature 32.04 CV Po/P0 500 1000 1500 2000 2500CO2 (To/T) ppm0100200300400500V po/p ppm:Coefficients:b[0] 1.2447899288e-4b[1] 0.1540627212b[2] -2.7406708246e-6b[3] 1.1305374947e-8b[4] -1.0258917696e-12r ² 1Calibration, Range, Sensitivity and LinearityLinearNon Linear10/22/20123ESPM 129 Biometeorology 5Analog to Digital Conversion of Weather Measurements, Historical DataFew Sensors, Max/Min Temperature and Rain Gauge, Data Written by Hand on PaperESPM 129 Biometeorology 6Contemporary Analog to Digital Conversion of Weather Measurements10/22/20124ESPM 129 Biometeorology 7CIMIS Automated Weather StationESPM 129 Biometeorology 8Digital Voltmeter10/22/20125ESPM 129 Biometeorology 9Programmable DataLogger• Single-Ended or Differential Voltage Reading– Numerous channels• Adjustable Ranges– 0 – 500 mv–0-5 volt• Control ports– Trigger Relays• Power output– 5 or 12 v• Pulse counterESPM 129 Biometeorology 10New Generation of Programmable Data Logger10/22/20126Digital vs AnalogDigital• Many Modern sensors output Digital Data.• Distinct values for 0s and 1s• Signal not susceptible to Noise• Merging Time Stamps from multiple Digital Signals is not Trivial• Information can be transferred over long distancesAnalog• Many First Principle Sensors are Analog• Requires Analog to Digital Conversion• Susceptible to Noise• Multiplexor can interface many different channels from slow sensors with common time stampESPM 129 Biometeorology 11ESPM 129 Biometeorology 12Bits resolution Range: 10 v256 (28) 0.03906 v/bit4096 (212) 0.00244 v/bit65536 (216) 0.000152 v/bitBit Resolution and RangeAnalog to Digital ConversionBits resolution Range: 10 v256 (28) 39.06 mv/bit4096 (212) 2.44 mv/bit65536 (216) 0.152 mv/bit10/22/20127ESPM 129 Biometeorology 13Stair Step with TC from course resolution A/D8 Bit A/D on 10 volt range resolves 1 C per bitESPM 2, The BiosphereTypical Micrometeorological Flux Instrument Station10/22/20128ESPM 129 Biometeorology 15New Wetland Site with Methane SensorESPM 129 Biometeorology 16Sonic Anemometer10/22/20129ESPM 129 Biometeorology 17Wind Velocity is a function of the time it takes to transmit Sound a known distance, d.More effective to take the reciprocal of the difference between the sent and transmitted sound pulses1211()2ddVtt1211()2dcttESPM 129 Biometeorology 18Sonic Temperature2403 (1 0.32 )asonicecTP1211()2ddVtt22221211 1() ( )1612 403sonic x ydTVVtt10/22/201210ESPM 129 Biometeorology 19Attributes of Sonic Anemometer• Small Transducer to path ratio• Measurement resolution, 1 to 10 mm s-1• Accuracy, 1% RMS or 1 to 4 cm s-1• Frequency Response, ~ 10 to 20 Hz (oversampled, block averaged)• Range, 0 to 60 m s-1ESPM 129 Biometeorology 20Cup Anemometer2d Sonic AnemometerPulse Counts Number of Revolutions10/22/201211ESPM 129 Biometeorology 21Net RadiometersVoltage is proportional to the Energy Absorbed and Measured with a Thermopile detecting the Temperature Difference between the Top and BottomESPM 129 Biometeorology 22Voltage is proportional to the Energy Absorbed and Measured with a Thermopile detecting the Temperature Difference between Dark and Bright ElementsPyranometer, Measures Solar Radiation10/22/201212ESPM 129 Biometeorology 23Pyranometer• Spectral response waveband:– 310 to 2800 nm • Time Response–4 s• Maximum irradiance: 2000 W/m² • Linearity– < 0.6% at 1000 W m-2• Sensitivity: – 5 to 15 µV/W/m²ESPM 129 Biometeorology 24Specifications Spectral range 400 -1100 nm Sensitivity (nominal) 100 µV/W/m2 Response time less than 1 s Max. irradiance 2000 W/m2 Temperature dependence +0.15 %/ºC (typical) Operating temperature -30ºCto+70 ºC Directional error ±5 % at 80 degrees Quantum Sensor, Measures Photon Flux DensityPhotons displace electrons in silicon and create current.10/22/201213ESPM 129 Biometeorology 25Diffuse RadiationESPM 129 Biometeorology 26Ione, Ca 2004PAR (mol m-2 s-1)0 500 1000 1500 2000 2500PAR Diffuse0200400600800100012001400160010/22/201214ESPM 129 Biometeorology 27Temperature/Humidity SensorESPM 129 Biometeorology 28Thermocouple10/22/201215ESPM 129 Biometeorology 29Type T thermocoupleemf, microvolt0 500 1000 1500 2000 2500Temperature, C0102030405060Thermocouples, type T, copper-constantan: ~ 40 V/CESPM 129 Biometeorology 30Thermistor10/22/201216ESPM 129 Biometeorology 31PRT Thermistor Thermocouplesensitivity 0.4 ohm C-1 0.1 to 1.5 kohm C-10.04 to 0.06 mv C-1accuracy +/- 0.1 C +/- 0.1 C +/- 0.35 CLinearity Slightly non-linearVery non linearSlightly non linearResponse time10 s 5 s < 5sExcitation yes yes NoT reference no no yesTemperature SensorsTemperature, unaspirated12 14 16 18 20 22 24 26 28Temperature, Aspirated121416182022242628Coefficients:b[0]: 0.7893957267b[1]: 0.9367525171r ²; 0.9931178141Temperature and Humidity Sensors Must be Shielded from the Sun and Aspirated!—Hence, Power is RequiredRelative Humidity, unaspirated20 30 40 50 60Relative Humdity, Aspirated202530354045505560At 20 C, the T difference is 0.611 C10/22/201217Hours0 400 800 1200 1600 2000 2400Air Temperature121416182022242628UnaspiratedAspiratedBiases between Aspirated and Unaspirated Thermometers are too Large,Compared to Gradients and Treatment Differences One Seeks to Quantify in NatureESPM 129 Biometeorology 34Temperature Sensors must be Shield from the Sun and Aspirated101214161820222426282030214523001513024540051563074590010151130124514001515163017451900201521302245Degrees CTimeAspiration Comparison of Two Campbell Sensors for TemperatureUnaspirated Campbell SensorTemperature10/22/201218ESPM 129 Biometeorology 35Rain GaugeESPM 129 Biometeorology 36Rain GaugeTipping Bucket10/22/201219ESPM 129 Biometeorology 37Soil Heat Flux PlateESPM 129 Biometeorology