Research On Model And Application Of Photosynthetically Active Radiation Estimation Based On Radiation Transfer Theory

Photosynthetically active radiation is the part of solar radiation used by plants for photosynthesis.Its wavelength range is 0.4-0.7?m.It is the energy source for photosynthesis of plants.It has an important influence on the growth and development of plants,and it is also a key parameters of terrestrial ecosystem model and climate model.Accurate estimation of photosynthetically active radiation has important significance and value for the study of ecology,agronomy,and climatology.At present,the estimation of photosynthetically active radiation is more dependent on ground observation data,and the sparse site causes uncertainty in its spatial distribution.At the same time,the estimation accuracy obtained by interpolation is also difficult to meet the needs of practical applications.Therefore,a new estimation model based on remote sensing and meteorological data can improve the spatial resolution and estimation accuracy of photosynthetically active radiation.On the basis of summarizing related researches of the predecessors,this paper uses the MODIS and meteorological data to establish a segmented radiation transmission model for estimating photosynthetically active radiation based on the radiation transmission theory.Using the ground observation data to verify the accuracy of the model,and inversion of the spatial pattern of photosynthetically active radiation in Beijing-Tianj in-Hebei Region.The main research contents and conclusions are as follows:(1)Based on the radiative transfer equation,refer to the Bird clear sky model to calculate the clear-air solar radiation,and consider the Stephens method for the effect of cloud on photosynthetically active radiation,using MODIS's water vapor,ozone,aerosol optical thickness,cloud optical thickness,etc.These datas are input parameters,and a segmented radiation transmission model for estimating photosynthetically active radiation under sunny,cloudy and cloudy conditions is constructed.(2)Select the radiation data from the meteorological observation station in the area to verify the model's estimation accuracy.The correlation coefficient between photosynthetically active radiation and actual observations estimated in this paper is between 0.80-0.89,the root mean square error is between 15.84-20.91 W/m2,and the relative average deviation is between 6.56-16.23%.The percentage error is between 8.19-13.73%.The model has the highest accuracy in estimating photosynthetically active radiation in sunny days,followed by cloudy and cloudy days.The main reason is that only the optical thickness of the cloud is taken into account when estimating the effect of clouds on photosynthetically active radiation,and the cloud structure and cloudiness are ignored,resulting in a slightly larger estimation error in cloudy conditions.The overall estimation accuracy of each site is higher in the northwest than in the southeast,which is mainly affected by air quality and cloud conditions.(3)The photosynthetically active radiation of Beijing-Tianjin-Hebei region in 2016 was between 1730.07 and 2678.30MJ/m2.The overall spatial distribution of the high-level northwest high in the southeast,the mountain slope is higher than the shady slope.Among them,the annual photosynthetically active radiation of the Bashang plateau is about 2600MJ/m2,that of the dam area is about 2400MJ/m2,and that of the Taihang Mountains is about 2300-2400MJ/m2,and the vast plain area is about 2000-2100MJ/m2.This spatial pattern is mainly influenced by the combination of geography,topography and atmospheric conditions.The photosynthetically active radiation of Beijing-Tianjin-Hebei region experienced significant seasonal changes.The photosynthetically active radiation in January was between 4.04-117.74MJ/m2,in April was between 151.40-321.07MJ/m2,in July was between 299.98-412.62MJ/m2,in October was between 27.77-127.25MJ/m2.The discrete degree of each month was April>July>October>January.Compared with the related research in the same region,the estimated photosynthetically active radiation was slightly lower.The main reason was that in recent years,the fog in the Beijing-Tianjin-Hebei region has become more and more serious,and the increase in aerosols has increased the weakening effect of solar radiation.In addition,more rainy weather in this year results in lower values of photosynthetically active radiation.