ERDAS Top of Atmosphere Correction
To do this calculation the Spatial Model extension was used with a *.gmdx file.
Select the Spatial Model file to use. This tutorial does not go into the creation of these files. You will need to learn to model this which is why for the beginner the costly atmospheric correction extension should be used or the data should be corrected in PCI. This correction requires a bit of math in modeller and research into appropriate correction values.
When you downloaded the data a metafile should have been included (MTL.txt) For the next dialogue box you will need to open this file and locate the following information.
SUN_ELEVATION = 22.16728313
REFLECTANCE_MULT_BAND_1 = 2.0000E-05
REFLECTANCE_MULT_BAND_2 = 2.0000E-05
REFLECTANCE_MULT_BAND_3 = 2.0000E-05
REFLECTANCE_MULT_BAND_4 = 2.0000E-05
REFLECTANCE_MULT_BAND_5 = 2.0000E-05
REFLECTANCE_MULT_BAND_6 = 2.0000E-05
REFLECTANCE_MULT_BAND_7 = 2.0000E-05
REFLECTANCE_MULT_BAND_8 = 2.0000E-05
REFLECTANCE_MULT_BAND_9 = 2.0000E-05
REFLECTANCE_ADD_BAND_1 = -0.100000
REFLECTANCE_ADD_BAND_2 = -0.100000
REFLECTANCE_ADD_BAND_3 = -0.100000
REFLECTANCE_ADD_BAND_4 = -0.100000
REFLECTANCE_ADD_BAND_5 = -0.100000
REFLECTANCE_ADD_BAND_6 = -0.100000
REFLECTANCE_ADD_BAND_7 = -0.100000
REFLECTANCE_ADD_BAND_8 = -0.100000
REFLECTANCE_ADD_BAND_9 = -0.100000
Although there are multiples of the Reflectance information, it is fairly clear that all values are the same. You input this data into the following dialogue as shown below.
If you select edit it will show you a workflow model. Otherwise select Run
The process dialogue box will open and show the progress.
Now if you look at your TOA Reflectance values. They should all be between 0 and 1.
I stopped here because I ran into all negative results.
We can rescale this to reduce the file size and give a distinct range to the values.