ABLE Radiometry / Vegetation State
These measurements provide valuable ground truth data for modelling efforts using satellite derived remote sensing information.
All measurements are made at 1 Hz frequency (except on the Smileyberg AWS system; 2 Hz) and averaged to 30 minute values. The measurements are considered to be representative of the grassland areas at their respective locations.
Photosynthetically Active Radiation (PAR):
This measurement (made with a silicon cell pyranometer) in the 400-700 nm waveband provides information on the intensity of radiation used by photosynthetic processes in plants.
Net radiation is the measurement of the difference in downwelling and upwelling broadband radiation (short wave and long wave). A net radiometer is used to make this measurement.
Albedo is the measurement of the difference in shortwave solar insolation and reflected shortwave energy from the surface. An albedometer is used to make this measurement.
Solar Insolation is the measuerment of shortwave solar insolation. The upper portion of an albedometer is used to make this measurement.
The temperature of the canopy surface is measured with three co-located (Whitewater only) infrared temperature sensors aimed to the NW, NE, and SE.
The canopy reflectance is measured to determine the reflectance of various solar wavelengths. A multispectral radiometer is used to perform this measurement at multiple locations.
Leaf Area Index:
Leaf area index is an important measurement reflecting the canopy structure and thus it's ability to intercept radiation. A PAR sensor is used to perform this measurement at multiple locations.
PAR: LI-COR, Inc., Silicon Cell Quantum Sensor, Model # LI-COR LI-190SA, Spectral response 400 to 700 nm, Accuracy +/- 5% of the reading.
Net Radiation: Radiation and Energy Balance Systems, Inc., Ventilated Net Radiometer, Model # Q*7.1, Accuracy +/- 5% of reading.
Albedo: Scientific Sales , Inc., Albedometer, Model # 3023-A, Spectral Resonse 0.3 to 3 microns, Accuracy not specified by manufacturer but it is approximately +/- 5% of the reading.
Solar Insolation: Scientific Sales , Inc., Albedometer (using upper portion only), Model # 3023-A, Spectral Resonse 0.3 to 3 microns, Accuracy not specified by manufacturer but it is approximately +/- 5% of the reading.
Surface Temperature: Everest Interscience, Inc., Infrared Temperature Transducer, Model # 4000 series, Spectral Resonse 8 to 14 microns, Accuracy +/- 0.5 deg. C.
Canopy Reflectance: Cropscan, Inc., Multispectral Radiometer, Model MSR87, 8 narrow wavebands (50 nm intervals) in the range 460-810 nm, Accuracy approximately +/- 5% of the reading.
Leaf Area Index: Decagon Devices, Inc., AccuPar, Model PAR-80, Spectral response 400 to 700 nm, Accuracy +/- 5% of the reading.
PAR is measured by the AWS systems at Smileyberg and Whitewater and is output as part of the AWS datastream.
Net radiation is measured by the EBBR station at Whitewater and output as part of the EBBR datastream. Net radiation is measured by the AWS system at Smileyberg and output as part of the AWS datastream. Net radiometers are ventilated to reduce loss of data from dew and frost and to reduce the effects of wind on the measurement.
Albedo is measured by the AWS systems at Whitewater and Smileyberg and output as part of the AWS datastream.
Solar insolation is measured by the AWS systems at Whitewater and Smileyberg and output as part of the AWS datastream.
Surface temperature is measured with three infrared temperature transducers mounted on the TDR box infrastructure and are output by a CR10X datalogger that also logs precipitation.
Canopy Reflectance and Leaf Area Index:
Canopy reflectance and Leaf area index are measured approximately every two weeks during the growing season at Smileyberg, Whitewater, and Brainerd. This process requires that multiple measurements be made in clear sky conditions at around noon solar time.
All measurements, except the MSR/LAI, are performed and logged by Campbell Scientific, Inc. CR10X dataloggers. Most radiometric instruments require periodic cleaning of their domes and replacement of dessicant. The ventilation of the net radiometers must be maintained to reduce the loss of data from dew and frost and to reduce the effects of wind on the measurement. Periodic calibration checks (every two years) of the radiometric sensors are made to ensure that calibrations have not changed. Bird detterrent spikes have been added to some of the radiometers to try to reduce soiling and puncturing (of the plastic net radiometer domes especially).
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