\(l_{1}=ln\left[\frac{\ \text{fr}_{PHU,1}}{\text{fr}_{LAI,1}}-\text{fr}_{PHU,1}\right]+l_{2}\bullet\text{fr}_{PHU,1}\) (4)
\(l_{2}=\frac{\left(\ln\left[\frac{\ \text{fr}_{PHU,1}}{\text{fr}_{LAI,1}}-\text{fr}_{PHU,1}\right]-ln\left[\frac{\ \text{fr}_{PHU,2}}{\text{fr}_{LAI,2}}-\text{fr}_{PHU,2}\right]\right)}{\text{fr}_{PHU,2}-\text{fr}_{PHU,1}}\) (5)