CWP and EO: GPP with LUE
Gross primary productivity (GPP) colloquially called "photosynthesis" is estimated in WaPOR with the Light Use Efficiency model.
In the LUE model, the relationship between light and photosynthesis rate is assumed linear, where the LUEmax parameter guides the slope of this relationship. Weather parameters (air temperature, air humidity, radiation intensity, soil moisture) act as stress factors to reduce LUEmax.
The light that goes to photosynthesis, photosynthetically active radiation, PAR, is another weather input. The ability of a plant to absorb PAR is driven by the plant's greenness and physiological state, expressed in the parameter fraction of absorbed PAR, fAPAR. fAPAR can be derived from NDVI.
Reading task:
Please, go through sub-section 2.1.6 Net primary productivity (raw pdf pp 42-47, document pp 30-37) of the WaPOR v2 methodology.
Take a look at Figure 24 (raw pdf p 76, document p 64) shows the fAPAR = f(NDVI) equation.
Answer the following questions:
- Do you have all the necessary information to reproduce the LUE equation used by WaPOR?
- what is the fAPAR from NDVI equation?
- what is the value of the PAR to total solar light fraction?
- what is the LUEmax value?
- how are temperature, radiation, humidity stress factors derived?
- how is soil moisture stress factor derived?
- What do the following three parameters represent in equation 34:
- εCO2, εAR, εRES
- which of them are related to vegetation and which to the environment?
- can the EO be used to retrieve them?