Using ASTER 15 m data

• ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is an imaging instrument flying on Terra, a satellite launched in December 1999 as part of NASA's Earth Observing System (EOS). ASTER is a cooperative effort between NASA, Japan’s Ministry of Economy, Trade and Industry (METI) and Japan's Earth Remote Sensing Data Analysis Center (ERSDAC). ASTER is being used to obtain detailed maps of land surface temperature, reflectance and elevation. ASTER captures high spatial resolution data in 14 bands, from the visible to the thermal infrared wavelengths; and provides stereo viewing capability for digital elevation model creation. For more information please see http://asterweb.jpl.nasa.gov/index.asp. ASTER L1B data is available on-demand via the USGS Global Visualization Viewer (http://glovis.usgs.gov).

• The following analysis was done using software from Wimsoft (http://wimsoft.com).

 

Table 1. ASTER bands

Band	Bandwidth (nm)	Pixel Size (m)	Remarks
VNIR = visible near-infrared
1	520 - 600	15
2	630 - 690	15
3N	760 - 860	15	N = normal
3B	760 - 860	15	B = backward looking at 26.7˚
SWIR = shortwave infrared
4	1600 - 1700	30
5	2145 - 2185	30
6	2185 - 2225	30
7	2235 - 2285	30
8	2295 - 2365	30
9	2360 - 2430	30
TIR = thermal infrared
10	8125 - 8475	90
11	8475 - 8825	90
12	8925 - 9275	90
13	1025 - 1095	90
14	1095 - 1165	90

Detailed instructions for ordering and processing ASTER data are given in Exercises_ASTER.pdf. A few examples are shown below.

1        Venice lagoon

The RGB composite was created from ASTER VNIR bands 1, 2 and 3N. ASTER does not have a real blue band and therefore the created RGB image does not look like a true-color image. Below is a small subset of a RGB image of the Venice lagoon of 2006/08/17. You can see a cloud of high reflectance due to suspended sediments just south of the city of Venice. The full size image is quite large (> 28 MB) and can be opened by clicking at the subset image below.

 

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The full image as well as images from other dates are available at http://spg.ucsd.edu/Satellite_Data/Venice.

A WAM utility wam_turbidity_aster calculates relative turbidity by subtracting ASTER band 2 from band 1. Itis convenient to represent turbidity as a grayscale image with turbid areas dark (black) and clear areas light (white). Note the high turbidity cloud south of Venice. You can notice that even the full resolution coastlines are not accurate for the 15-m ASTER data..

 

2        San Diego

 

A RGB composite from ASTER bands 1, 2 and 3N of the San Diego area on 2005/11/16 is shown below. The full size image is quite large (> 20 MB) and can be opened by clicking at the subset image below.

 

 

Outflow from the Los Buenos creek, affected by the Mexican sewage treatment plant can be seen on this image.  Increased turbidity in the outflow plume is shown below.

 

 

 

Aster images are suitable for visualization with Google Earth (http://earth.google.com/download-earth.html). After you have installed Google Earth, you can create a KML file for your ASTER (it is easy to create, see Exercises_ASTER.pdf) and then just clicking on the KML file starts Google Earth that would load your specified image. The ASTER PNG file will overlay the original Google Earth image of the area. The PNG file is about 27-30 MB in size and may take a while to download. In the screen shot example below, the Google earth data is in the top part and the overlaid ASTER data below it. As you can see, the navigation of the ASTER data is excellent and the two parts match very well. This way you can read, for example, the place names from Google Earth.

 

 

You can try to load the full ASTER image of the San Diego area into Google Earth with the following KML file and the Venice image with the following KML file. Please be patient as after Google Earth starts (which is slow) it takes another minute or more to load and overlay the ASTER image.

 

It should be noted that ASTER was designed for land applications and therefore the sensitivity of its VNIR bands is not sufficient to see much structure in the open ocean. However, in near-shore turbid environments ASTER data can be useful.