GE 5180 Exercise Digital topography and satellite imagery of volcanic edifices

Problem: How can topographic form (and satellite imagery) be used advantageously to help in the understanding of volcanic shape and the volcano itself?

Background information:Francis & Oppenheimer --Chapter 13Web Tutorial by Sorenson

Required Materials: PC with access to ENVI and ArcView and/or Surfer 8, such as ones in 211 or 709 Dow

Activities: 1. Select a volcano from Central America. The following ones have available data: Guatemala: Agua, Pacaya, Acatenango, San Pedro, Toliman, Atitlán, Cerro Quemado (Almolonga)El Salvador: Santa Ana, Izalco, San Salvador, San Vicente, Tecapa, San MiguelNicaragua: San Cristobal, Casita, Telica, Momotombo, Mombacho, ConcepcionEcuador: Tungurahua2. Download the needed DEM data in NAD 27 from its server address, as listed by Sorenson. This could also require more than one quadrangle and mosaicing.3. Display the DEM data as a shaded relief map. Experiment with different lighting and view angles.4. Look up the corresponding information from the GVN data base(Also note the Central America DVD from Smithsonian)5. Locate best (cloud-free) ASTER image from the archive of Central American Volcano ASTER data.6. Learn to display ASTER data as an RGB false color image. Select one RGB combination that shows details at the volcano7. Wrap this image on the digital topography.8. Use Google Earth and compare results. Comment on the comparison.9. Discuss the possible conclusions of your work with respect to the understanding of the volcano.Hints and other things to consider: This work should help you to find the boundaries of the volcanic edifice. What is the nature of the basement topography?Where are the vents of this vvolcano?What faults can be seen?Are stages of volcano growth obvious?Can you see individual volcanic units (lava flows, pyroclastic flows, debris avalanches, etc)?Anticipated outcomes: As a result of this activity, which might require a few hours of effort, you may be able to:Learn how to manipulate DEM data to examine topography.Learn how to interpret the topography of a volcano using DEM and satellite RS imagery.Learn a valuable preparatory activity for field work or remote sensing.

Instructions on how to locate and display ASTER images:

ASTER data are available in \\coe\slush\bluthdata\HistoricVolcanoes or \\coe\Faraday2\bluthdata\HistoricVolcanoes. All images are L1A processing level, unless they are in a folder which says L1B, L2 or DEM. L1A images contain raw digital numbers and do not have an associated map coordinate system. Daytime images have VNIR, SWIR, and TIR bands and are ~113,000 KB, and nighttime images have only SWIR and TIR and are ~36,000 KB. VNIR (Visible Near Infrared) are bands 1, 2, and 3N and have a spatial resolution of ~15m/pixel, SWIR (Shortwave Near Infrared) are bands 4, 5, 6, 7, 8, and 9 and have a spatial resolution of ~30m/pixel, and TIR (Thermal Infrared) are bands 10, 11, 12, 13, 14 and have a spatial resolution of ~90m/pixel. In order to locate the best cloud-free image, you will have to visually assess each image in ENVI. If you can’t locate the volcano in the ASTER image, you can use Google Earth to help you identify the volcano.

In ENVI, go to File Open Image File navigate to HistoricVolcanoes, display by Details, choose a daytime or nighttime image and click OPEN. Bands for daytime images load automatically into the Available Bands List, but for nighttime images you have to manually choose ImageData bands from the HDF Dataset Selection window.

To display any 3 band combination, in Available Bands window select on RGB Color, select R and click on a desired band, e.g. Band 3N, select G and click on a desired band, e.g. Band 2, select B and click on a desired band, e.g. Band 1, and click on LOAD RGB. Here is an example a 3-2-1 band combination of Pacaya volcano in Guatemala from 03 February 2004.

Instructions on how to georeference ASTER images:

In order to wrap an ASTER image on digital topography, you will need to associate the image with a map coordinate system by georeferencing the image.

In ENVI, open your cloud-free image and go to Map Georeference ASTER Georeference Data. In the Input ASTER Image window, select an input file. The first file in the list contains the VNIR bands (under File Information, should have Dims: 1400 x 4200 x 3), the third file in the list contains the SWIR bands (under File Information, should have Dims: 2048 x 2100 x 6), and the fourth file in the list contains TIR bands (under File Information, should have Dims: 700 x 700 x 5). If you only want the area around the volcano, click Spatial Subset Subset Using Image, and manually define an area around the volcano and click OK. The Pacaya example for georeferencing the VNIR is below.

In the Georeference ASTER Data window select Output Map Projection as UTM, Datum as North America 1927, and Units as Meters. The zone will automatically be recognized. Leave Number Warp Points X: 50, Y: 50. Enter an Output GCP (Ground Control Points) Filename and leave Perform Bow Tie Correction as Yes. Click OK.

In Registration Parameters window, select Output Result to File, enter a filename, leave all default settings and click OK.

Open the georeferenced image in ENVI and display as an RGB.

Instructions on how to overlay an ASTER image on digital topography with ArcGIS:

In order to overlay an ASTER image on a DEM in ArcGIS, the ASTER image must (1) have the same projected coordinate system as the DEM, and (2) be in a format that ArcGIS can read. ArcGIS cannot read HDF files, so convert the image to an .IMG file (ERDAS IMAGINE).

In ENVI, open the georeferenced ASTER HDF file. Go to File Save File As ERDAS IMAGINE. Select the input file and spatial subset (optional), click OK, and in the Output Parameters window give the output file a name and click OK again.

To overlay the ASTER image on the DEM, launch ArcScene from the ArcGIS menu in the Start Menu. Add the ASTER image to the Table of Contents by clicking on the Add Data icon (black cross in the yellow triangle) on the Standard Toolbar. Select the georeferenced ASTER image and click Add. In the Table of Contents, right-click on layer name click on Properties click on Base Heights tab and click on the open folder icon to Obtain heights for layer from surface. Select the NAD27 DEM as the Surface and click Add. In Layer Properties window, click OK.

To change the RGB band combination in ArcGIS, in the Table of Contents, right-click on layer name click on Properties click on Symbology tab. Under Show, select RGB Composite and use dropdown arrows to change band combinations.

Instructions on how to overlay an ASTER image on digital topography with Surfer:

In order to overlay an ASTER image on a DEM in Surfer, the ASTER image must (1) have the same projected coordinate system as the DEM, and (2) be in a format that Surfer can read. Surfer cannot read HDF files, so convert the image to a TIFF file.

In ENVI, open the georeferenced ASTER HDF file. Go to File Save File As TIFF/GeoTIFF. Select the input file and spatial subset (optional), click OK, and in the Output Parameters window give the output file a name and click OK again.

In Surfer, to add the DEM as a Surface go to Map Surface select DEM as Grid file and click OK. To add the ASTER image as a Base Map go to Map Base Map and select the .TIF ASTER image and click Open.

The TIFF ASTER image has pixel coordinates, but it needs UTM coordinates in order to overlay it on the DEM, so you will have to manually change the x, y coordinates to UTM coordinates. You can either look in the metadata for the UL (Upper Left) corner coordinates and calculate the

LR (Lower Right) corner coordinates, or you can use the pixel locator in ENVI to manually get the corner coordinates.

To look at the metadata, with WordPad open the metadata .HDR file that was created with the georeferenced image. The UL (Upper Left) UTM map coordinates are given in “map info,” highlighted in yellow in the VNIR Pacaya example below. The first number is the easting (xmin coordinate) and the second number is the northing (ymax coordinate).

ENVI description = {Create Layer File Result [Fri Oct 05 13:18:31 2007]}samples = 4935lines = 4696bands = 3header offset = 0file type = ENVI Standarddata type = 4interleave = bsqsensor type = Unknownbyte order = 0map info = {UTM, 1.000, 1.000, 724964.927, 1629484.212, 1.5000000000e+001, 1.5000000000e+001, 15, North, North America 1983, units=Meters}wavelength units = Unknownband names = { Warp (ASTER VNIR Band1:AST_L1A_00302032004164215_20070119101622_8774.hdf), Warp (ASTER VNIR Band2:AST_L1A_00302032004164215_20070119101622_8774.hdf), Warp (ASTER VNIR Band3N:AST_L1A_00302032004164215_20070119101622_8774.hdf)}wavelength = {0.556000, 0.661000, 0.807000}

To calculate the LR coordinates, use the following equations,

LR easting = Xmax = xmin + (# samples * spatial resolution in x direction)LR northing = Ymin = ymax - (# lines * spatial resolution in y direction)

where samples (columns) and lines (rows) are found in the metadata (highlighted above in green) and spatial resolution in x direction = 14.9970 m and spatial resolution in y direction = 14.9968 m. Recall that the spatial resolution for the VNIR is ~15m/pixel.

Alternatively, open the georeferenced ASTER image in ENVI, and go to Tools Cursor Location/Value to use the cursor to manually get the UL and LR map coordinates of the entire image.

In Surfer, right-click on the ASTER image base map, and click on the Base Map tab to change the Image Coordinates to UTM map coordinates. This essentially converts the TIFF to a GeoTIFF.

To overlay ASTER image on the DEM, go to Edit Select All, then Map Overlay Maps.

The default display settings are not so pretty, so right-click on the composite image Properties change Resample Method to Nearest, change Overlay Resolution to 1024, and in Color Modulation select Use overlay color only and click OK.