Remote Sensing Image Processing using GRASS: Lesson 4

Contents: Display of satellite images (Landsat ETM+) in the UTM coordinate, production of vegetation index (NDVI) image (GUI-based manipulation) Display of elevation data (SRTM) in the latitude-longitude coordinate, mosaicing, 3D display Prodcution of ASTER NDVI in the UTM coordinate, calculation of brightness temperature using thermal band, 3D display (Application) Extraction of flooding area using temporal vegetation and water indies data, instructed by Dr. Masayasu MAKI

The image finally obtained in this Lesson 4

Creation of folder for MODIS data in the latitude-longitude coordinate

After starting GRASS, click the lower right button of "Projection values" in the GRASS window

1. Determination of LOCATION, MAPSET, DATABASE:

   LOCATION:  latlon2
   MAPSET:    PERMANENT
   DATABASE:  /home/student
   
   After filling the above information, "Esc" + "Enter"
   

2. Selection of projection: Latitude-longitude coordinate

   Please specify the coordinate system for location <utm>
   
   A   x,y
   B   Latitude-Longitude
   C   UTM
   D   Other Projection
   RETURN to cancel
   
   >B (after typing, "Enter")
   

3. Selection of datum:

   Do you wish to specify a geodetic datum for this location? (y/n) [y] y
   
   Please specify datum name
   Enter 'list' for the list of available datums
   or 'custom' if you wish to enter custom parameters
   Hit RETURN to cancel request
   
   >list
   
    (Many datum are displayed)
   Short Name  Long Name / Description
   
    (skip)
   tokyo   Tokyo       (bessl ellipsoid)
   wgs72   WGS_1972    (wgs72 ellipsoid)
   wgs84   WGS_1984    (wgs84 ellipsoid)
   
   Please specify datum name
   Enter 'list' for the list of available datums
   or 'custom' if you wish to enter custom parameters
   Hit RETURN to cancel request
   
   >wgs84
   
   Now select Datum Transformation Parameters
   Please think carefully about the area covered by your data
   and the accuracy you require before making your selection.
   
   Enter 'list' to see the list of available Parameter sets
   Enter the corresponding number, or <RETURN> to cancel request
   
   >list
   
   Number Details
   ---
   1    Used in whole wgs84 region
        (PROJ.4 Params towgs84=0.000,0.000,0.000)
        Default 3-Parameter Transformation (May not be optimum for older datums;
    use this only if no more appropriate options are available.)
   ---
   
    (skip)
   
   >1
   
   
                     DEFINE THE DEFAULT REGION
   
   
                ====== DEFAULT REGION ======
                | NORTH EDGE: 15          |
                |                          |
     WEST EDGE  |                          |EAST EDGE
     102    |                          |108
                | SOUTH EDGE: 10          |
                ============================
   
     PROJECTION: 3 (Latitude-Longitude)      ZONE: 0
   
                       GRID RESOLUTION
                           East-West:     0.00429
                         North-South:     0.00429
   
   
   After filling the above information, "Esc" + "Enter"
   

-> A window of GRASS will show up.

Move of MODIS image files

Notice: You can move the files either by using Explorer on Windows or by typing a command (mv) on Cygwin

Import and display of MODIS image files

Here, use Enhanced Vegetation Index (EVI) and Normalized Difference Water Index (NDWI) images in the latitude-longitude coordinate derived from MODIS images

1. Change of working directory: Move to the directory where the image files exist. (No need for GUI user)

   > cd /home/student/latlon2/PERMANENT
   

2. Import of image files (Easier to do so by using GUI)　←　Each file (e.g. 200-2004evi_cambodia.tif) is composed of 46 images

   > r.in.gdal input=2003-2004evi_cambodia.tif  output=evi
   > r.in.gdal input=2003-2004ndwi_cambodia.tif  output=ndwi
   

3. Display the imported images (Easier to do so by using GUI)

   > d.mon x0
   > d.rast evi.red
   
   > r.colors map=evi.red rules=evi (reading color table for EVI image)
   > d.rast evi.red
   

   Notice: Repeat the same process for evi.green, evi.blue, ..., evi.46, ndwi.red, ndwi.green, ..., ndwi.46

Extraction and count of "Water" pixels for each day

1. Import of image files (No need if you have completed this process in "Import and display of MODIS image files")

   > r.in.gdal input=2003-2004evi_cambodia.tif  output=evi
   > r.in.gdal input=2003-2004ndwi_cambodia.tif  output=ndwi
   

2. Selection of the area (No need if you have completed this process in "Creation of folder for MODIS data in the latitude-longitude coordinate")

   > g.region w=102 e=108 n=15 s=10 res=0.00429
   

3. Extraction of "Water" pixels (for each day)

   > r.mapcalc "water1=if(evi.red==0, 0, ndwi.red>=evi.red, 1)"
   　　　　　　　　　　　　　　　　　　・
   　　　　　　　　　　　　　　　　　　・
   　　　　　　　　　　　　　　　　　　・　
   > r.mapcalc "water46=if(evi.46==0, 0, ndwi.46>=evi.46, 1)"
   

4. Count of "Water" pixels (for each day)

   > r.stats -c input=water1
   　　　　　　　　　・
   　　　　　　　　　・
   　　　　　　　　　・　
   > r.stats -c input=water46
   
   (Example of output "r.stats -c input=water1")
   
   0 1231368  ← [0]: other,  [131368]: Total number of "other" pixels
   1 16206    ← [1]: water,  [16206]: Total number of "water" pixels
   * 383660
   

Display of maximun and minimun "water area" images

1. Display of the image files

   > d.mon x0
   > d.rast water??　← minimun "water area" image
   > d.mon x1
   > d.rast water???　← maximun "water area" image
   

Reference

• Introduction to GIS, Dr. Kenlo NASAHARA (NISHIDA, maiden name), Tsukuba University, Japan (written in Japanese)