A method to estimate instantaneous and daily intercepted photosynthetically active radiation using a hemispherical sensor

A method to estimate instantaneous and daily intercepted photosynthetically active radiation... Intercepted photosynthetically active radiation (IPAR) is an important variable in vegetation processes such as photosynthesis, and water and energy exchange. Measurement of this quantity and the related fractional interception efficiency (f PAR )) can be time consuming because of the need to sample for spatial and temporal variability. A method is presented for estimation of IPAR and f PAR using a commercially available hemispherical radiation sensor (Li-Coy LAI-2000) originally designed for the estimation of canopy leaf area index. This instrument provides sufficient information on the structure of the canopy and the angular dependence of light interception for single measurements to be interpreted for all solar zenith angles. These data can be used to infer instantaneous direct and diffuse interception as well as the daily integrated values. The method was tested in a millet crop and a shrub fallow area in semi-arid West Africa. LAI-2000 estimates were compared with a more traditional method using PAR sensor arrays. The errors in estimation of instantaneous IPAR were small at most times of day, rising to a maximum of 15–30 W m −2 at solar noon, when incident PAR was more than 400 W m −2 . Instantaneous f PAR estimates exhibited some bias towards underestimation at small solar zenith angles, and overestimation at larger angles, particularly on the shrub fallow site. These errors were generally small (much less than 0.l unit of f PAR ). Daily IPAR was estimated to within 7% of the direct PAR sensor measurements. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Agricultural and Forest Meteorology Elsevier

A method to estimate instantaneous and daily intercepted photosynthetically active radiation using a hemispherical sensor

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Publisher
Elsevier
Copyright
Copyright © 1995 Elsevier Ltd
ISSN
0168-1923
D.O.I.
10.1016/0168-1923(94)02196-Q
Publisher site
See Article on Publisher Site

Abstract

Intercepted photosynthetically active radiation (IPAR) is an important variable in vegetation processes such as photosynthesis, and water and energy exchange. Measurement of this quantity and the related fractional interception efficiency (f PAR )) can be time consuming because of the need to sample for spatial and temporal variability. A method is presented for estimation of IPAR and f PAR using a commercially available hemispherical radiation sensor (Li-Coy LAI-2000) originally designed for the estimation of canopy leaf area index. This instrument provides sufficient information on the structure of the canopy and the angular dependence of light interception for single measurements to be interpreted for all solar zenith angles. These data can be used to infer instantaneous direct and diffuse interception as well as the daily integrated values. The method was tested in a millet crop and a shrub fallow area in semi-arid West Africa. LAI-2000 estimates were compared with a more traditional method using PAR sensor arrays. The errors in estimation of instantaneous IPAR were small at most times of day, rising to a maximum of 15–30 W m −2 at solar noon, when incident PAR was more than 400 W m −2 . Instantaneous f PAR estimates exhibited some bias towards underestimation at small solar zenith angles, and overestimation at larger angles, particularly on the shrub fallow site. These errors were generally small (much less than 0.l unit of f PAR ). Daily IPAR was estimated to within 7% of the direct PAR sensor measurements.

Journal

Agricultural and Forest MeteorologyElsevier

Published: May 1, 1995

References

  • Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique
    Chazdon, R.L.; Field, C.B.
  • Terrestrial ecosystem production: a process model based on global satellite and surface data
    Potter, C.S.; Randerson, J.T.; Field, C.B.; Matson, P.A.; Vitousek, P.M.; Mooney, H.A.; Klooster, S.A.
  • Inclined point quadrats
    Warren, Wilson J.; Reeve, J.E.

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