数据说明
SeaWiFS Photosynthetically Active Radiation(PAR)
上传时间:2019-05-23 00:05:52 浏览次数:作者与来源:admin
Photosynthetically active radiation is defined as the quantum energy flux from the Sun in the spectral range 400-700 nm that photosynthetic organisms are able to use in the process of photosynthesis.
Unit: Einstein/ m2/d
Resolution:  9km pixel, daily, monthly
Duration: Sep. 1997 to Dec. 2010.
Source: Sea-viewing Wide Field-of-view Sensor(SeaWiFS), NASA
Version: 2018
Processing: Original daily and monthly mean products are shown.
 
The PAR model uses plane-parallel theory and assumes that the effects of clouds and clear atmosphere can be de-coupled. The planetary atmosphere is therefore modeled as a clear sky atmosphere positioned above a cloud layer. Under solar incidence θs, the incoming solar flux at the top of the atmosphere,E0×cos(θs) is diminished by a factorTdTg/(1-Sa×A) by the time it enters the cloud/surface system. In this expression, Td is the clear sky diffuse transmittance, Tg is the gaseous transmittance, Sa is the spherical albedo, and A is the cloud/surface system albedo. As the flux,E0×cos(θs)TdTg/(1-Sa×A), passes through the cloud/surface system, it is further reduced by a factor A. The solar flux reaching the ocean surface is then given by
E=Eclear(1 –A)(1 –As)-1(1-Sa×A)-1
where As is the albedo of the ocean surface andEclear=E0cos(θs)TdTg is the solar flux that would reach the surface if the cloud/surface system were nonreflecting and non-absorbing.
Known issues
1. A limited set of satellite-to-in-situ match-up validation results are available for SeaWiFS from the validation tool of the SeaWiFS Bio-Optical Archive and Storage System (SeaBASS). And the result shows a mean bias of 7.87348 and a mean absolute error(MAE) of 8.03692.
2. As detailed in Frouin, Franz, and Werdell (2002), however, the validity of the PAR product improves with temporal compositing. The PAR product is primarily intended for use as a Level-3 product, where data have been composited over weekly to monthly time-scales.
3. It is worth noting that the products here are mainly used to estimate the PAR of the global ocean. When estimating the PAR of a regional area, it is necessary to use the measured PAR data to verify the applicability of the products presented here.
Reference
Frouin, R., McPherson, J., Ueyoshi, K., & Franz, B. A. A time series of photosynthetically available radiation at the ocean surface from SeaWiFS and MODIS data. Remote Sensing of the Marine Environment II., 2012,8525:852519 DOI: 10.1117/12.981264
Frouin, R., Franz, B. A., & Werdell, P. J. The SeaWiFS PAR product. ,In: S.B. Hooker and E.R. Firestone, Algorithm Updates for the Fourth SeaWiFS Data Reprocessing, NASA Tech. Memo. 2003-206892, Volume 22, NASA Goddard Space Flight Center, Greenbelt, Maryland, 46-50.The SeaWiFS PAR product, 2002.
Frouin, Robert, and Rachel T. Pinker. Estimating Photosynthetically Active Radiation (PAR) at the earth's surface from satellite observations. Remote Sensing of Environment, 1995,51(1):98-107. DOI: 10.1016/0034-4257(94)00068-X
All the contents of this page are quoted from NASA. All project documentation and related publications can be found at the website: https://oceancolor.gsfc.nasa.gov/