System and method for observing plant canopy photosynthetically active radiation absorptivity

Abstract

The invention discloses a system and method for observing plant canopy photosynthetically active radiation absorptivity. The system comprises a first photosynthetically active radiation acquisition unit which is a first set distance away from the top of the canopy of a plant and located above the canopy of the plant, a second photosynthetically active radiation acquisition unit which is a second set distance away from the ground, and a data acquirer receiving data acquired by the first photosynthetically active radiation acquision unit and the second photosynthetically active radiation acquision unit. By the adoption of the system and method, automatic observing and recording can be achieved, cost, errors and man-made interference of manual measurement are reduced, real-time and long-time-series data can be obtained, and real-time automatic continuous plant canopy photosynthetically active radiation absorptivity observation can be achieved on the premise that universality is high, using is convenient and precision is high.

Description

technical field [0001] The invention relates to the technical field of plant remote sensing, and more particularly relates to an observation system and method for the absorption ratio of photosynthetically active radiation in a vegetation canopy. Background technique [0002] The ratio of the photosynthetically active radiation absorbed by vegetation to the photosynthetically active radiation reaching the top of the vegetation canopy is called the fraction of absorbed photosynthetically active radiation (FPAR). FPAR is an important input parameter for inversion of Gross Primary Productivity (GPP) by light utilization rate model, and FPAR can also be used as an indicator of vegetation coverage and change. The common FPAR retrieval method is to use the normalized difference vegetation index NDVI and MODIS Enhanced Vegetation Index (Enhanced Vegetation Index, EVI) to obtain. Within a certain range, there is a linear relationship between FPAR and NDVI. For example, in the CASA...

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Problems solved by technology

Among them, the main algorithm in NASA's FPAR product algorithm is to describe the spectral and directional characteristics of the canopy based on the 3D radiative transfer model. Considering the particularity of radiative transfer in the vegetation canopy, the 3D radiative transfer model is decomposed into two sub-models: When the radiation field in the layer is the radiation of the black body background and the radiation of the anisotropic emission source at the bottom of the canopy is considered separately, the reflectance and absorptivity of the canopy are considered as the weighted average of the two, and the accuracy of this calculation method is not high

Chen et al. also established the equations of FPAR, surface albedo, canopy porosity, and LAI based on the radiative transfer theory. The model considered the part of the photosynthetically active radiation reflected by the soil background that was absorbed by the canopy, and used this method for inversion In the NPP model, but this method does not take into account the reflection of photosynthetically active radiation by the vegetation canopy, and the calculation structure also has certain inaccuracies

Tao Xin combined the radiative transfer model and the geometric optics model to give the expression of FPAR. The parameters of this method are difficult to obtain and the calculation process is complicated.

In addition, the existing methods for observing the absorption ratio of photosynthetically active radiation are all realized by handheld devices, which cannot be observed in real time, automatically and continuously. Therefore, the data of daily and seasonal changes in FPAR cannot be obtained, which brings certain benefits to the verification and accuracy evaluation of FPAR. limitations

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