tailieunhanh - Biomass and Remote Sensing of Biomass Part 9

Tham khảo tài liệu 'biomass and remote sensing of biomass part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Introduction to Remote Sensing of Biomass 151 about 40 of the converted energy for dark respiration. Therefore the maximum photosynthetic efficiency is This result applies to c4 plants so-called because their first product of photosynthesis is 4-carbon sugar . For c3 plants like wheat and rice the efficiency is lower due to photorespiration effects. Remote sensing of radiation intensity Solar constant The average solar irradiance received outside the earth atmosphere is called Solar Constant. The intensity of solar radiation above the earth s atmosphere has nearly constant value unlike irradiance received at the ground. It s average value is 1367 W m2 though it shows some variation due to variations in solar activity. Annual fluctuations due to Earth-Sun distance give rise to a variation of of the extra-terrestrial irradiance and are given by Eo E0 1 2 365 D-3 2 where E0 is the mean value of solar constant D is the Julian days. Radiation reflected and received by the ground Radiation received at the ground surface is a combination of direct radiation which comes from the sun after passing through a path length in the transparent atmosphere and diffuse radiation which is radiation reflected by clouds and scattered by atmosphere in general. The contribution of diffuse radiation to irradiance received by ground depends on the atmospheric thickness moisture content cloud frequency turbidity of the atmosphere and angle of zenith. The radiation that is reflected from the ground is very small compared to that reflected from the clouds. Its value depends on the reflectance of different earth surface features. In many cases surface albedo is taken to be uniform across the land. Atmospheric effects Atmosphere plays a major role at attenuation and reflection of light that pass through it. Their main effects are reflection absorption and scattering depending on the wavelength and air mass ratio. .