I encountered a disruptive problem while following a step-by-step guide of the Land cover supervised classification from a document accessed from https://arset.gsfc.nasa.gov/sites/default/files/land/webinars/Advanced_Land_Classification/supervised_exercise_v2.pdf


I downloaded a Landsat 8 image from the Glovis website – [Path 43, row 33] for date 22nd September, 2015.

I unzipped the folder it was saved in to extract the contents using 7-zip folder.

1st Purpose was to convert the image to Top of Atmosphere (TOA) reflectance

In the Pre-processing icon of the Semi-automatic Classification(SCP) panel, in the part ‘Directory containing Landsat bands’ I put the folder containing the 11 bands of my downloaded Landsat 8 image.

In the ‘Select MTL file’ I manually input my .MTL text file that is the same directory folder of my Landsat 8 bands (it didn’t appear automatically as the documents says in pg.2, I don’t know why).

My metadata appeared anyway, for all 11 bands. I clicked the run icon at the bottom right to run the process.

It really took some time to run in my Windows 7 Starter 32 bit Dell Laptop; using Qgis 2.18.11 ‘Las Palmas’. Anyway, this is where the problems started.

I then proceeded to click on the ‘Band set’ icon located at the top of the SCP toolbar.(pg.3 of the exercise).

Bands 2-7 appeared, in tandem with the exercise. I clicked on ‘Create raster of band set (stack bands) then I clicked on the ‘Run’ icon at bottom right.

This process didn’t take long as the other one of converting to TOA reflectance.

However, the result, which is supposed to be a Bstack_raster.tif image was the astonishing bit. I got a Bstack_raster.tif image alright, but the issue was that it was pitch black.

The Problem:

My Bstack_raster.tif image was pitch black. So I right-clicked it and went to its Properties section – to ‘Style’ in order to display it in a usable color combination.

I put band 5 in the red band, band 4 in the green band and band 3 in the blue band. My contrast enhancement was set to ‘Stretch to MinMax’.

I then clicked ‘Load’ (in the section under Load min/max values) and then clicked ‘Ok’ but my Bstack_raster.tif image was still pitch black.

From my personal overview, the reason is because all my ‘min’ values in the red, green and blue band sections read ‘nan’. Yet, I have followed each step diligently in the exercise.

Troubleshooting efforts:

I have tried to backtrack all my steps above to see any errors but none identified so far.

I have repeated the same process thrice with the same results.

I have followed all the steps of pg.1-4 of the exercise without omission.

Problem Statement:

Please advice to convert the pitch black Bstack_raster.tif image to a usable color combination as shown in pg.4 of the exercise. A converted image of TOA is detrimental for my further uses.

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