Getting heavy noise after terrain correction with snappy

Schinken · December 1, 2020, 11:52pm

Good evening,
I am currently trying to find objects in sentinel data through a python script on a novice level. The problem I keep running into is after my terrain correction I get heavy noise in the .tif.

This is the code I am working with:

github.com

Schinkenspicker/Questions/blob/main/geotiffeditor.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "# works in snap36 env with python 3.6\n",
    "# analog to tutorial pdf\n",
    "\n",
    "import numpy as np\n",
    "import matplotlib\n",
    "import matplotlib.pyplot as plt\n",
    "import matplotlib.colors as colors\n",
    "import os\n",
    "\n",
    "import snappy\n",
    "from snappy import Product\n",
    "from snappy import ProductIO\n",

This file has been truncated. show original

If I open the original file directly in SNAP it looks like this, which makes detections easy:

After I run it through the code I get lots of noise and it looks like this if saved and opened in SNAP again:

Is there a way to keep the easily distinguishable form of the first picture even after the terrain correction or remove the noise through other means?

On another note: why can I do the terrain correction with the “Intensity_VV” but not “Intensity_VH”. It just gives me the following error:

AttributeError: ‘NoneType’ object has no attribute ‘getRasterWidth’

Thank you for your time.

ABraun · December 2, 2020, 7:36am

is it just a matter of color stretching?
Please make sure in the color manipulation tab that you apply the same min/max values to the terrain corrected band as in the first image.

Schinken · December 3, 2020, 2:24am

Thank you for your answer.

You are right, It seems it was because I used the min,max from the tutorial. Is there an option in snappy to just take one, kinda like in SNAP itself, don’t know where he takes the min,max from or just randomly assings them.

Could you also please help me with the other question, why can’t I do the terrain correction with the Intensity_VH and instead I just get the error ‘NoneType’ object has no attribute ‘getRasterWidth’

Thank you for your time.

ABraun · December 3, 2020, 7:49am

Maybe this is a misunderstanding. The min/max values are only a visual parameter wich allows you to enhance the contrast of the image when you display it. The pixel values of the rasters are not affected by the processing. So if you apply 100000 as vmax to plot it in snappy, you have to enter this in SNAP as well to get the same image visualization there.

Aout the missing VH band: You specify
parameters.put('sourceBands', "Intensity_VV")

in your script, so only this one is processed in the terrain correction.