Demonstrating tools in SAGA GIS to analyze Burned areas from Forest Fires

Introduction

In recent years forest fires have increased globally at a rapid rate destroying many hectares of vegetation, ecosystems and landscapes (Parajuli, 2019). Being able to analyse forest fires in multiple open source applications like SAGA GIS will benefit anyone looking to study the results of forest fires. Being able to manipulate raster files in many open source software will allow you as a user to to be able to pick and choose what software is better suited for your needs.

Downloading Saga

This tutorial uses the newest version of SAGA GIS, Version 8.4.1 64bit which can be downloaded here: https://sourceforge.net/projects/saga-gis/files/latest/download

Downloading Imagery from USGS

The first thing we will do to start off the tutorial will be finding data to run our analysis on. This tutorials imagery is found through USGS Earth Explorer. To actually download the data you have to make an account which is sound on the top right hand corner of the page, click login and it will bring you to a sign in page. At the Bottom it will ask if you want to Create New Account? This only requires a Username and Password of your choice. Once completed your able to start downloading imagery.

Selecting an Area of Interest

When selecting an area of interest in Earth Explorer it gives you many options of how to find the imagery you want. Your able to search for a selected name, search through states or feature types. In this tutorial we will be creating a polygon to choose our selected area.

Underneath the Geocode section you will see the Polygon tab. Select the tab and then go to your area of interest. Ours is Fort McMurry, you'll then left click to create the four corners of the polygon. The coordinates do not have to match but roughly in the same area.

Choosing a Date Range

Underneath the Polygon tab you'll see a tab for Date Range. We will be looking at before and after the Fort McMurray Fire so we will need dates before and after the fire started and finished. The dates I selected were 05/05/2015 to 10/10/17.

Cloud Cover

Beside the Date Range tab is the Cloud Cover tab. This tab allows you to reduce the amount of imagery that is unusable due to cloud cover. 28% was the selected out of cloud cover allowed. After selecting the amount you can click on the Data Sets button to bring you to your search results.

Imagery Selection After Fire

Before getting to results page you'll have to select the data sets you want. The files we want are found in the Landsat > Landsat Collection 2 Level-1 > Landsat 8-9 OLI/TIRS C2 L2. Once selected, click results.

When choosing imagery we want the clearest image we can find. Too see what each image looks like select the button you can see highlighted in the image below. As seen in the image below, the dates 2017/09/04 with path 42 and rows 020 and 021 were very clear so they were chosen for the analysis.

Imagery Selection Before Fire

When selecting the imagery for before the fire, 2015/05/10 had the clearest imagery that matched after the fires path and row.

Downloading the Imagery

To download your selected imagery, on each image you will have to select the download button which can be seen highlighted in red.

Then a download options window will open up and you will select Product Options. Then the image below will appear and you will be downloading all files, so selecting the entire bundle, as seen in red.

Converting Files

Some computers may have a hard time opening a Tar file. If you are unable to open the downloaded file, you may need to download a Tar file opener. For this tutorial we be using Winzip as the extension because windows does not know how to open Tar files. To download click this link:

https://www.winzip.com/en/pages/download/winzip/?lang=en&hd=Download%20Zip%20Opener%20Program%20With%20Ease&x-target=ppc&promo=ppc&gclid=CjwKCAiAp7GcBhA0EiwA9U0mtndQCHoDBslB2Ano7laabRDk7K2uevxb9LbHyebSrkqR614vUW11ZxoCUpIQAvD_BwE

Once the application opens - find your tar files in your files and then drag them into the window pane. Once in WINZIP select the unzip tab shown below and then click My PC or Cloud to unzip the files to a specified location on your PC. Then we you go back into your files, the folders will be accessible.

Downloading Files into SAGA

To download multiple files into SAGA you can either select them from your files in the bottom window pane or you can go through Geoprocessing > Imagery > Landsat > Landsat Import with Options which allows you to select from all your files. Beside files select the 3 dots to open file manager. Selecting imagery from after the fire we will be adding six files, Bands B4, B5 and B10 from row 42 and Path 20 and 21.

Highlighted in red in the row and path.

Once both after fire imagery is uploaded you'll be able to see the images in the right map pane. If not able to see you can right click on the bands you want and add to map. Adding them to the same map will over lap them.

After this is completed do the same process for the before fire imagery for both paths.

Mosaicking Two Rasters Together

This is just a demonstration of how to mosaic two rasters together for both before and after fire. If you want access a longer area of interest you can add the two sets of before imagery and after imagery. You'll find this tool in Geoprocessing > Grid > Grid Systems > Mosaicking.

When the mosaicking window opens for each band you'll add the two path and row selections together. So Band 4's Path 42 and rows 20 and 21 will be merged together for each band. Just select the two bands and hit the single arrow to move the over and then hit okay.

After for each band you'll want to rename them so your able to differentiate. I renames all bands After fire B4, After fire B5, etc. Then hit okay.

Then you'll want to rename the Grid so you know what your working on.

Then for each Grid for before and after the fire you'll want to rename as well to Before fire Mosaic and After fire Mosaic.

The results for Band 4 before and after will look like this in the map pane.

Fire Extent

To get the fire extent first we will clip the grids together. Go to Geoprocessing > Grid > Grid System > Clip Grid. Select the first grid to work with which will be After fire Mosaic.

Then move all three bands over selecting the double arrows. And select okay.

This should be what the window looks like after adding the bands.

Under the options panel you'll want to make sure the extent is the same as your map. If everything matches up select okay.

Too see what was just created. Select After Fire B10 and add to map.

The imagery below is the After Fire B10 New Grid.

The new grid will appear in your data manager and you will want to rename the grid to Clipped Grid.

Adding the new clipped layers to the map pane.

Below are the results of the fire extent for before and after the Fort McMurray Fire.

Difference of Before and After Fire

Geoprocessing > Grid > Calculus > Grid Difference

Object Based Image Segmentation

Geoprocessing > Imagery > Segmentation > OBIA > Object Based Image Segmentation

Calculating Area of Fire