HR: 1340h
AN: B33E-1673    [Abstracts]
TI: Evaluation of Two New Models of Net Radiometers and Comparison to a Model to Predict Net Radiation
AU: * Blonquist, J M
EM: mark@apogee-inst.com
AF: Apogee Instruments, Inc., 721 W 1800 N, Logan, UT 84321, United States
AU: Tanner, B D
EM: bert@campbellsci.com
AF: Campbell Scientific, Inc., 815 W 1800 N, Logan, UT 84321, United States
AU: Bugbee, B
EM: bruce.bugbee@usu.edu
AF: Plants, Soils, and Climate Dept. Utah State University, 4820 Old Main Hill, Logan, UT 84322, United States
AB: Net radiation is a key component to the surface energy balance, but it is difficult and expensive to measure accurately. Two new net radiometer models (Hukseflux NR01 and Kipp & Zonen CNR2) have been released in the past year. We evaluated and compared these models to two Kipp and Zonen model CNR1 net radiometers, and to two less expensive, older model net radiometers (Kipp & Zonen NR-Lite and REBS Q*7.1). Additionally, we predicted net radiation from solar radiation, air temperature, and absolute humidity measurements using a commonly used model that calculates net longwave radiation using a Brunt (1932; 1952) approach for predicting net emissivity. The model uses the ratio of measured solar radiation to predicted clear-sky solar radiation as a surrogate for cloud cover. Net shortwave radiation is determined by direct measurement of solar radiation and the albedo of the surface. Hourly averages and daily totals (over the course of the study; 33 days) from three replicate sensors of the two new net radiometers compared quite well to the CNR1 radiometers. The difference was generally less than +/- 5 %. Three replicates of the two older model net radiometers did not agree as well with the newer models, with differences generally less than +/- 15 %. Our data matched what others (Cobos and Baker, 2003; Brotzge and Duchon, 2000) have shown for these older radiometers. The net radiation model yielded hourly average and daily total values that were 10-15 % higher than the CNR1 radiometers. Our findings indicate that accuracy increases with increasing cost. Prediction of net radiation from the model yielded adequate results for some applications, such as evapotranspiration predictions and irrigation scheduling, but the model has considerable error at night due to some simplifying assumptions. Accurate net radiation measurements depend on proper placement of the sensor, proper leveling, and routine maintenance to keep the sensing surfaces clean.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0452 Instruments and techniques
SC: Biogeosciences [B]
MN: 2007 Fall Meeting