Estimation of incident Photosynthetically Active Radiation from MODIS Data
Estimation of incident Photosynthetically Active Radiation from MODIS Data
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Date
2006-08-08
Authors
Liang, Shunlin
Zheng, Tao
Liu, Ronggao
Fang, Hongliang
Tsay, Si-Chee
Running, Steven
Advisor
Citation
Liang, S., T. Zheng, R. Liu, H. Fang, S. C. Tsay, S. Running, (2006), Estimation of incident Photosynthetically Active Radiation from MODIS Data, Journal of Geophysical Research - Atmosphere, 111, D15208, doi:10.1029/2005JD006730
DRUM DOI
Abstract
Incident photosynthetically active radiation (PAR) is a key variable needed by almost
all terrestrial ecosystem models. Unfortunately, the current incident PAR products
estimated from remotely sensed data at spatial and temporal resolutions are not sufficient
for carbon cycle modeling and various applications. In this study, the authors develop a
new method based on the look-up table approach for estimating instantaneous
incident PAR from the polar-orbiting Moderate Resolution Imaging Spectrometer
(MODIS) data. Since the top-of-atmosphere (TOA) radiance depends on both surface
reflectance and atmospheric properties that largely determine the incident PAR, our first
step is to estimate surface reflectance. The approach assumes known aerosol properties
for the observations with minimum blue reflectance from a temporal window of each
pixel. Their inverted surface reflectance is then interpolated to determine the surface
reflectance of other observations. The second step is to calculate PAR by matching the
computed TOA reflectance from the look-up table with the TOA values of the satellite
observations. Both the direct and diffuse PAR components, as well as the total shortwave
radiation, are determined in exactly the same fashion. The calculation of a daily average
PAR value from one or two instantaneous PAR values is also explored. Ground
measurements from seven FLUXNET sites are used for validating the algorithm. The
results indicate that this approach can produce reasonable PAR product at 1 km resolution
and is suitable for global applications, although more quantitative validation activities are
still needed.