44 sample plots were selected from the whole image. The mean value of the band in each plot was used for building the relationship.

Sample plots, the back ground are original image and landsat 7 (right side)

Sample plots, the back ground are original image and landsat 7 (right side)

Here is for mean value for each plots

## (Intercept)     (slope) 
##  -5852.5607    130.2715 
##   cor 
## 0.959 
##  P.value 
## 1.47e-24

## (Intercept)     (slope) 
##  -1068.6356    146.1588 
##   cor 
## 0.926 
##  P.value 
## 2.04e-19

## (Intercept)     (slope) 
##   -1421.218     102.133 
##   cor 
## 0.941 
##  P.value 
## 2.01e-21
## Nonlinear regression model
##   model: ORI ~ a + b * L7_ori^2 + c * L7_ori
##    data: band4
##         a         b         c 
## 12399.697     2.545  -265.752 
##  residual sum-of-squares: 4149616
## 
## Number of iterations to convergence: 1 
## Achieved convergence tolerance: 8.063e-08