HR: 0800h
AN: B51A-0928    [Abstracts]
TI: Intercomparison of Photosynthetically Active Radiation Measurements Obtained With Different Sensor Types at Hokkaido, Japan
AU: * Dye, D
EM: dye@jamstec.go.jp
AF: JAMSTEC Frontier Research Center for Global Change, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001 Japan
AU: Endo, T
EM: tendo@iis.u-tokyo.ac.jp
AF: Insitute of Industrial Science, University of Tokyo, Ce-508,4-6-1 Komaba, Meguro-ku,, Tokyo, 153-8505 Japan
AU: Yasuoka, Y
EM: yyasuoka@iis.u-tokyo.ac.jp
AF: Insitute of Industrial Science, University of Tokyo, Ce-508,4-6-1 Komaba, Meguro-ku,, Tokyo, 153-8505 Japan
AB: Field and simulation studies have indicated that accurate modeling of terrestrial photosynthesis and ecosystem-atmosphere carbon dioxide exchange at daily and sub-daily timescales requires information on the diffuse and beam fluxes of photosynthetically active radiation (PAR, 400-700 nm). Such data provide a critical basis for analyzing and monitoring the effects of clouds and aerosols on vegetation productivity and the terrestrial carbon cycle, and for validation of remotely sensed satellite estimates of PAR. In practice, diffuse PAR and global PAR are typically measured in situ, and beam PAR is calculated as the difference of these two fluxes. Whereas time-series data on instantaneous diffuse PAR for seasonal and longer periods were uncommon in the past, growing recognition of their importance in carbon cycle studies has led to increased deployment of PAR sensors capable of measuring both diffuse and global PAR fluxes. Improved information and understanding of the relative accuracy of PAR measurements obtained with different sensor types is important as a basis for determining the confidence limits of model results and to enable meaningful comparison of data sets. In this study, we examine measurements of diffuse and global PAR (photosynthetic photon flux density, PPFD) measured during 2004 at Hokkaido, Japan, with two relatively new and unique types of PAR sensors: the Multifilter Rotating Shadowband Radiometer (model MFR-7 from Yankee Environmental Systems, Inc., custom-configured for PAR) and the Sunshine Sensor (model BF3 from Delta-T Devices). As a reference data set, we employ measurements of the global flux of spectral solar irradiance obtained with a spectral radiometer (from Eko Instruments, Co., Ltd.), from which we calculate PPFD. The results provide insight into the potential uncertainty or error associated with measurements of diffuse and global PAR from two common sensor types and with application of the data to models of vegetation photosynthesis and ecosystem-atmosphere carbon dioxide exchange.
DE: 3394 Instruments and techniques
DE: 0315 Biosphere/atmosphere interactions
DE: 0360 Transmission and scattering of radiation
DE: 0394 Instruments and techniques
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting