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Compare band combinations

In this lesson, you'll take an initial look at the burn scar using Landsat 8 imagery. After acquainting yourself with the study area, you'll change the band combination of the imagery to better see the burned areas. Then, you'll create a custom combination to emphasize burn scars.

Open the project

Before you begin your analysis, you'll download and open a project package containing the raw data for your assignment.

  1. Go to the Montana Fires item details page.

    Montana Fires is a project package. Project packages contain all maps, data, folders, and toolboxes for a project.

  2. Click Download and save the file.

    Montana Fires item details page

    Next, you'll open the project inArcGIS Pro.

    Note:

    You can also click Open in ArcGIS Pro to open the project directly in ArcGIS Pro.

  3. Start ArcGIS Pro. If prompted, sign in using your licensed ArcGIS account.
    Note:

    If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.

    When you open ArcGIS Pro, you're given the option to create a new project or open an existing one. If you've created a project before, you'll see a list of recent projects.

  4. Click Open another project (if you've used ArcGIS Pro before) or Open an existing project (if you haven't.)

    Next, you'll search for the project you downloaded.

  5. In the Open Project window, browse to the location where you downloaded the Montana Fires project package. Double-click the package to open it.

    Default project

    The project opens with three layers in the Contents pane. The first two are imagery layers and are turned off. The third layer is a polygon feature class showing the extent of Glacier National Park in Montana, which comprises more than a million acres. Fires are a natural part of the regional ecology, but it is critical for forest management services to track their extent.

Enhance the imagery

Now that you've accessed the project data, you'll look at and enhance the imagery. The project came with two Landsat 8 imagery layers, clipped to a study area around two particular wildfires: the Thompson Fire and the Reynolds Creek Fire. Both images were captured in August of different years.

  1. In the Contents pane, check the box next to the 2014 layer to turn it on. Right-click the layer and click Zoom To Layer.

    2014 default

    The image is dark and difficult to see. You'll adjust the brightness, contrast, and gamma to better see the image. Brightness determines whether an image is lighter or darker. Contrast determines how distinguishable features are from one another. Gamma determines the relationship between how an image detects light and its actual luminescence. Increasing all of these will improve the visibility of the image.

  2. In the Contents pane, click the 2014 layer to select it.
  3. On the ribbon at the top of the application, click the Appearance tab. In the Enhancement group, increase the Layer Brightness to 20, the Layer Contrast to 25, and the Layer Gamma to 1.8.

    Enhancement

    The changes occur immediately on the image.

    2014 corrected

    You can now see the environment in more detail. The mountainous terrain is marked by valleys and lakes. Some of the peaks are snowcapped while others are obscured by cloud cover. Since this image was taken in August, the mountains may have glaciers or permanent snow. The terrain also appears to have ample vegetation. The type of vegetation and the slope of the mountains affect fire, particularly the speed at which it spreads. This is what the area looked like in 2014, before the Reynolds Creek and Thompson fires. Next, you'll take a look at the 2015 imagery.

  4. In the Contents pane, uncheck the 2014 layer to turn it off. Check the 2015 layer to turn it on.

    2015 default

    The default appearance of the 2015 image is clearer than the 2014 image was, but it could still use some brightness, contrast, and gamma correction.

  5. In the Contents pane, click the 2015 layer to select it.
  6. On the Appearance tab, increase the Layer Brightness to 10, the Layer Contrast to 15, and the Layer Gamma to 1.5.

    2015 corrected

    The 2015 imagery has two distinct differences from the 2014 imagery. First, a large gray cloud covers the central-southern portion of the image. This cloud is actually smoke from the Thompson fire, which was still burning when this image was taken.

    Thompson fire

    Secondly, to the upper left of the lake in the central-northern part of the image is a long reddish streak. This is the burn scar of the Reynolds Creek fire, which had stopped burning by the time this image was taken.

    Reynolds Creek fire

    While both fires are visible, their exact boundaries are unclear. Next, you'll change the band combination of the imagery to emphasize the fires.

View different band combinations

Landsat imagery measures ranges of wavelengths of the electromagnetic spectrum, including some that are invisible to the human eye. These ranges are called "spectral bands." The bands are described in the following table:

Number Name What this band shows best

1

Coastal Aerosol

Shallow water, fine dust particles

2

Blue

Deep water, atmosphere

3

Green

Vegetation

4

Red

Man-made objects, soil, vegetation

5

Near Infrared

Shorelines, vegetation

6

Shortwave Infrared 1

Cloud penetration, soil and vegetation moisture

7

Shortwave Infrared 2

Improved cloud penetration, soil and vegetation moisture

8

Panchromatic

Black-and-white imagery, crisper detail

9

Cirrus

Cirrus clouds

10

Thermal Infrared 1

Thermal mapping, estimated soil moisture

11

Thermal Infrared 2

Improved thermal mapping, estimated soil moisture

Bands 2, 3, and 4 (Blue, Green, and Red) make up the spectrum of light visible to the human eye. The Natural Color band combination, which your imagery currently uses, combines these three bands to approximate how imagery would look to a person. Next, you'll change the band combination to emphasize the fires and better see their boundaries.

  1. In the Contents pane, click the 2015 layer to select it.

    Natural Color bands

    Beneath the layer name are the bands the image currently uses: the Blue, Green, and Red bands that encompass visible light. The Red and Green bands emphasize vegetation, which can be useful for seeing fires because of the contrast between highly vegetated areas untouched by fire and areas where vegetation has been destroyed by fire. Using another band that emphasizes vegetation, like Near Infrared (band 5), could improve the contrast.

  2. On the Appearance tab, in the Rendering group, click Band Combination and choose Color Infrared.

    Band Combination

    The image changes to show the new band combination. In the Contents pane, the bands beneath the layer name also change, indicating that this image combines Near Infrared, Red, and Green bands (3, 4, and 5).

    2015 Infrared

    In this image, vegetation appears as red. Both fire areas appear as dark brown. Compared to the original image, the fires appear more clearly, especially the Reynolds Creek fire north of the lake. However, the Thompson fire is still obscured somewhat by smoke. Next, you'll try a band combination using the Shortwave Infrared bands (6 and 7), which penetrate clouds.

  3. On the Appearance tab, click Band Combination and choose Land/Water Interface.

    2015 SWIR

    The bands beneath the layer in the Contents pane change to both Shortwave Infrared bands and the Near Infrared band, meaning this image combines bands 5, 6, and 7. Although the main purpose of this combination is to delineate land and water, it also penetrates haze (or, in this case, smoke). Almost no smoke appears around the Thompson fire, making its boundaries much clearer. However, the burned areas appear orange while the surrounding mountain slopes appear yellow. This makes the Reynolds Creek fire, which spreads into the mountains, more difficult to see.

  4. Click Band Combination again and choose Vegetation Analysis.

    2015 Vegetation

    This combination uses the Red, Near Infrared, and Shortwave Infrared 1 bands (4, 5, 6). It thus combines the emphasis of vegetation from the Color Infrared combination with some of the haze penetration of the Land/Water Interface combination. Although some smoke is visible around the Thompson fire and the Reynolds Creek fire blends somewhat into the mountain slopes, these issues are less severe than in the previous combinations.

    If the haze could be reduced just a little more, this image would probably be the best for digitizing the burn scars. However, none of the remaining default band combinations improves on the three you looked at. To tailor the imagery to your needs, you'll create a custom band combination.

Create a custom band combination

So far, you've used preconfigured band combinations. Next, you'll choose your own bands to create a custom band combination that will improve on the Vegetation Analysis band combination by further reducing haze.

  1. In the Contents pane, locate the 2015 layer.

    Vegetation Analysis bands

    The Vegetation Analysis band combination uses the Shortwave Infrared 1 band to reduce haze and the Near Infrared and Red bands to emphasize vegetation. Switching Shortwave Infrared 1 to Shortwave Infrared 2 would improve the haze (or cloud) penetration.

    Note:

    Since bands like Near Infrared and Shortwave Infrared cannot be seen, imagery displays them as RGB (Red Green Blue) composites. This means that red light or color is used to display the imagery in the band with which it's associated, and so on for the green and blue bands. Any band can be used in any of the three composite colors, which is why it's possible to have the Red band displayed using blue light. The color of the symbol and the first word indicates the composite color, while the second word indicates the band.

  2. Right-click the ShortWaveInfrared_1 band and choose ShortWaveInfrared2.

    ShortWave Infrared 2

    Note:

    The Panchromatic band (band 8) and both Thermal Infrared bands (bands 10 and 11) have been removed from the data, which is why they do not appear in the list of bands.

    The band automatically changes, as does the image on the map. Since the change was between two similar wavelengths, the differences on the map are not incredibly obvious, but change did occur. Next, you'll replace the Red band with the Blue band.

  3. Right-click the Blue color and choose Blue.

    Blue band

    The image on the map changes slightly. Although still visible, the haze has been reduced.

    2015 custom

    To easily access this band combination in the future, you'll save it as one of the default combinations on the Appearance tab.

  4. On the Appearance tab, click Band Combination and choose Custom.

    The Custom Band Combination window opens.

  5. For the Red color, choose ShortWaveInfrared_2. For the Green color, choose NearInfrared. For the Blue color, choose Blue.

    Custom Band Combination

  6. Name the custom band combination Burn Scar Analysis and click Add.

    The band combination is added to the drop-down menu when you click the Band Combination button, allowing you to quickly apply it to other imagery (or reapply it to this image if you change the band combination again).

    Note:

    You can remove custom band combinations from the list only after starting a new session of ArcGIS Pro.

  7. Save the project.

In this lesson, you displayed imagery of two fires in Glacier National Park, first as a natural color image and then using other band combinations that emphasized the burned areas better. Ultimately, you created a custom band combination specifically meant to highlight burn scars. Although this custom combination is more suitable for deriving exact burn scar boundaries, it still requires some visual interpretation in order to determine what is burned and what is not. In the next lesson, you'll use a mathematical formula called a "burn index" to calculate burned areas quantitatively, providing an even more exact measure of where the fires raged.