SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
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EXERCISE 1 –
Preparing ASTER images
In this exercise, we will begin to work with ASTER images, the goal being to transform the data into
a product usable image interpretation / classification.
Create a composite RGB image
1. Image preparation
We will work with the visible and near infrared bands (VNIR), which have a horizontal spatial
resolution of 15 meters. They are numbered like so and have the following characteristics:
A. Composite bands:
i. We will create a composite image using three bands: V1,V2, y V3N.
1. In ArcCatalog
open the following directory:
C:/Taller_SERVIR/1_ASTER/ASTER_images
2. Review the properties of the individual ASTER bands:
a. Right click on a band and select Properties, which will open up
a window like the one below that shows you the information
about the band you are about to manipulate.
b.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
After revising this information, fill in the table below:
Wavelength
Band
Visible and near infrared V1, V2, V3N & V3B
(VNIR)
Shortwave infrared (SWIR)
Thermal infrared (TIR)
Resolution
15 m
Q. How many composite RGB images could one obtain using the data in this folder?
A.
Q. What date were these scenes taken?
A.
Q. What spatial reference do these data have?
A.
After this, we’ll open ArcMap , and create a composite RGB images with different bands:
1. First we’ll add the three bands to our data view in ArcMap by using the “Add Data”
button
or by dragging them in from ArcCatalog (make sure they’re from the
same date and scene). Note: Save this project in: C:/Taller_SERVIR/1_ASTER/
ASTER_images, with a name like “AST_dd-m_year_1”
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
2. Now we will group together these three individual bands into one image. To do this,
open ArcToolbox
, and Data Management Tools, Raster, Raster Processing.
Double click Composite Bands.
3. We will now fill in the Input Rasters section with the layers in order (V1, V2, V3N),
and name the new image so that it reflects the place and date, using “.img” as an
extension.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
4. Now we have an image composite with three bands. We can change the order of the
bands to see the image in different color combinations. Right click on the image and
select Properties/ Symbology
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
5. Repeat the same steps using the VNIR bands for the other scene.
Note: to maintain a little more order Turing these processes, you can remove
the original bands from ArcMap. You should also differentiate the names of
the composite images even if they have the same date and general location.
6. Observe the images’ characteristics.
a. What can you make out in the image so far?
b. What numerical value(s) do clouds have?
c. What numerical value(s) does water have?
d. Identify some differences between the characteristics of the two composite
images.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
7. Now we want to eliminate the “0” values around each image. We will use the Copy
Raster tool found in: ArcToolbox/Data Management Tools/Raster/Raster Dataset
After this process, we will have images without blank data surrounding them.
8. Now we will proceed to improve the visual quality of these images. Using spectral
stretching, we will manipulate the histograms of each image in order to find a
combination that leaves the two images with more comparable colors; however, this
process will not change the numerical values of the images.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
What is a histogram?
In this case, it is a graph that
represents the quantity of
pixels of each digital number
per band.
Example of a histogram with different levels of contrast
Right click on the image and select “Properties.” In the window that opens, click on the
“Symbology” tab. Under Stretch select “Histograms.”
Imagen con estiramiento
Imagen con estiramiento
Image with stretching
Image without stretching
Note: You can also adjust the color stretching by changing the
number of Standard Deviations. Try with different options.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
B. Elaborating a mosaic (ArcMap)
After generating the RGB composites, we can construct a mosaic, which will allow us to
work with the two images together as one (as they look on the screen). To do this, we’ll
use the Mosaic to New Raster tool, found in: ArcToolbox/Data Management
Tools/Raster/Raster Dataset
In the “Mosaic to New Raster” window, choose the images to be joined.
• In Output location, indicate the folder in which the new output will be saved
C:/Taller_SERVIR/1_ASTER/ ASTER_images
• Raster dataset name: type the name of the mosaic to be generated
“AST_pa_2006”
• Coordinate system: click on the icon to the right, select “Import” and navigate
to any of the bands that you were originally working with (this process will
import the same geographic reference used in those rasters)
• Cell size: type 15 (since the image is has a resolution of 15 meters)
• Number of Bands: 3
•
Follow the screenshot above to fill in the rest of the fields. Click
When this process finishes, we’ll have one new RGB image composed of the two original
images (previously individual), containing their original characteristics.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
Mosaic Q. How would you define a mosaic?
A.
Q. What happens when you change the position of each band?
A.
Activity:
Eliminate the values around the color mosaic and describe the steps taken:
1.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
C. Build a model:
Now we will carry out the same processes above in a summarized form.
When there is a large number of data that require the same exact processing steps, it
is often more efficient to construct models to automate such processes. Upon
documenting each step needed for certain analyses, we can take advantage of this
software to systematically prepare these satellite images for our use, without having
to repeat steps over and over again.
•
•
•
•
First, right click on ArcToolbox
and select “New Toolbox.” We’ll create a new toolbox
named “Modelo”
In this new toolbox, right click again and select New/ “Model”
A new window should open up where we will edit our new model.
Here we will bring in all of the steps realized earlier in this exercise. Briefly, these were:
o Add the 3 bands per scene
o Composite these bands to make RGB images
o Combine these images to make one mosaic
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
o Eliminate the value “0”
1. To start, we’ll add
the data view.
the three bands from each scene (V1, V2 and V3) to
2. In order to make these layers more legible, we can edit the name in the Table
of contents as shown below.
3. Then we will add these bands to the model, simply by selecting all six and
dragging them into the empty model window.
4. Now we will add the first tool to the model: “Composite bands”, which is
found in ArcToolbox/Data Management Tools/Raster/Raster Processing.
Just select the tool and drag it to the model window. We’ll do this twice since
there are two scenes.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
5. Using the model connection icon
, connect the three bands to the
“Composite band” tool. Make sure the order in which you connect these
bands is correct.
6. Review each composite band tool (double click on the Bellow box) to make
sure that the output file, folder and name are appropriate.
(C:/Taller_SERVIR/1_ASTER/ ASTER_images). Again, we will do this
for both scenes.
Note: Here you can verify that the bands are in the correct order.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
7. Add the next tool Mosaic to New Raster, which is found in ArcToolbox
Data Management Tools/Raster/Raster Dataset/
/
8. Select the connection tool
to make the outputs of the composite bands the
inputs of the Mosaic to New Raster tool.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
9. Revise the parameters in the “Mosaic to New Raster” box, and fill in the
remaining parameters as shown below:
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
10. Now we will eliminate all of the “0” values around the resulting mosaic. To
do this, drag the “Copy Raster” tool into the model window. This tool should
be in ArcToolbox/ Data Management Tools/Raster/Raster Dataset/.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
11. Once again, we’ll select the connection tool
Mosaic to new raster to the “Copy raster” tool.
to connect the output of
12. Edit the “Copy Raster” parameters by double clicking on its box. We will use
the same parameters used in the previous step.
13. In the final result of the mosaic, right click and select “Add to display”. This
will make the result of “Copy Raster” appear in the data view alter the model
is run successfully.
14. Run the model by clicking the “Model” menu and selecting “Run Entire
Model”.
15. The final product should appear in the ArcMap data view. Is this what you
were expecting?
16. Play with the band combination in the image properties.
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
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SERVIR Workshop: Disaster Management and Response to Extreme Events
Preparing ASTER images
Review of spectral bands in different optical sensors MSS
I
0.40
TM / ETM+
ASTER
0.50
0.55
1: 0.433 0.453
0.70
1: 0.50 0.60
1: 0.45 0.52
2: 0.52 0.60
2: 0.60 0.70
BLUE
GREEN
0.60
0.65
II
Near IR
3: 0.63 0.69
2: 0.63 - 0.69
4: 0.63 - 0.69
1: 0.620 - 0.670
4: 0.76 0.90
3: 0.76 - 0.86
5: 0.775 0.805
15: 0.743 - 0.753
6: 0.845 - 0.89
2: 0.841 - 0.876
7: 1.2 - 1.3
5: 1.23 - 1.25
Mid IR
5: 1.55 1.75
1.55
1.60
1.65
7: 2.08 2.35
2.30
3.00
8.00
8: 1.55 - 1.75
4: 1.6 - 1.7
2.10
2.20
IV.
11: 0.526 - 0.536
4: 0.80 1.10
0.80
0.85
III
3: 0.459 - 0.479
1: 0.52 - 0.6
2: 0.45 - 0.515
3: 0.525 0.605
3: 0.70 0.80
0.75
1.20
1.30
MODIS
VIOLET
VIOLET
0.45
ALI
5: 2.145 6: 2.185 7: 2.235 8: 2.295 9: 2.360 -
2.185
2.225
2.285
2.365
2.430
6: 1.628 - 1.652
9: 2.08 - 2.35
7: 2.105 - 2.155
TIR
10: 8.125 - 8.475
11: 8.475 - 8.825
12: 8.925 - 9.275
6: 10.4 12.5
13: 10.25 - 10.95
14: 10.95 - 11.65
14.00
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