CEE 6150 Digital Image Processing 1 Lab 3: Image data sources

Searching for Image data on the web Locating U.S. satellite and aircraft image data (free). EarthExplorer: http://earthexplorer.usgs.gov/ AVIRIS: http://aviris.jpl.nasa.gov/ This lab introduces the search engines for free image data collected by U.S. satellites and aircraft using the EarthExplorer and AVIRIS web tools. Since we will be dealing with spectral data, the two systems of greatest interest are the two hyperspectral imaging systems, AVIRIS and Hyperion, but we will also consider multispectral imagery from the Operational Land Imager.

GOAL: locate and identify imagery from the AVIRIS (aircraft) and Hyperion (EO-1 satellite) and the OLI (Landsat-8) systems covering the same area during the same time period. Area of Interest: A scene containing desert and agricultural land just northwest of the Salton

Sea, near Mecca and Thermal, CA.

Characteristics:

• Hyperion is a hyperspectral imaging system flying on the EO-1 satellite. It is considered to be a research system – a test of hyperspectral imaging from space. While it was used to collect data worldwide, the data are sparse in time and space, collected only at the specific request of researchers . The Hyperion data are also relatively noisy and this will be apparent in the radiometrically corrected data.

• The AVIRIS (Airborne Visible InfraRed Imaging Spectrometer) is an imaging spectrometer flown on aircraft, usually at high altitude (20 km or 60,000 ft). AVIRIS is also considered to be a research system, however the system is well calibrated and the radiometric and geometric corrections are generally excellent. AVIRIS is based in Southern California, and most of the flights are within flight range of the base. Thus, the preponderance of imagery is in California and adjacent states. We will use imagery from 2013 since those data have been atmospherically corrected. The AVIRIS data will serve as a reference data set.

• The OLI (Operational Land Imager) is an operational satellite imaging system, and the newest in the Landsat Series. It is a polar orbiting system designed to provide repeat coverage worldwide at 16 day intervals. The system is well-calibrated and provides frequent, predictable coverage.

Procedure: 1. Search for Hyperion data. The Hyperion data availability will constrain our search. We

will limit our search to data collected in 2013, since the best calibration for both the AVIRIS and the OLI are from that year.

2. Search for AVIRIS data that coincide with the Hyperion data. The AVIRIS is flown in this region rather frequently, and there is a good chance that there will be data that are roughly coincident with the Hyperion scenes that are available. Select the AVIRIS scene that best matches a Hyperion scene in location and time.

3. Search for OLI data. Since the OLI data are collected on a predictable schedule, it is likely that there will be data available within 2-3 weeks of the AVIRIS scene.

CEE 6150 Digital Image Processing 2 Lab 3: Image data sources

Select Hyperion scenes that meet selection criteria 4. Log in to EarthExplorer: http://earthexplorer.usgs.gov/ 5. Under the Search Criteria tab

a. In the map area, drag and zoom to the general location. Navigate to Southern California and zoom in to a region around the Salton Sea (the large lake).

b. Under Coordinates, select Use Map. This will define a polygon that spans the extent of the map area.

c. Zoom out one level. This will allow you to see the polygon vertices.

d. Refine the selected area by adjusting the polygon vertices. You may also add or delete vertices.

e. Under Date Range limit the search period to 2013 6. Under the Data Sets tab, select EO-1 > EO-1 Hyperion 7. Under the Additional Criteria tab:

a. Select the acceptable cloud cover level, e.g., < 30% b. Select the processing level, L1R

• Level 1R (L1R) = Radiometric corrections to compensate for variations due to detector sensitivity. This processing level is only available for Hyperion data. L1R products are provided in HDF format.

• Level 1Gst (L1Gst) = Radiometric and systematic geometric corrections derived from spacecraft ephemeris data have been applied while employing a 90-meter Digital Elevation Model (DEM) for topographic accuracy. L1Gst scenes are provided in GeoTIFF format.

• Level 1T (L1T) = Radiometric and systematic geometric corrections incorporating ground control points. L1T scenes are provided in GeoTIFF format.

8. Under the Results tab you will get a list of all the images meeting the selected criteria. To get a visual of the locations, select the Show Results Control dropdown menu, and select Show all Footprints …

This will display all of the available scenes as colored boxes on the map. Alternatively, select Show All Browse …

This will display browse images of the available scenes on the map. 9. If necessary, return to the Search Criteria tab and adjust the boundaries of the polygon

or the selection criteria to refine the selection. 10. Repeat steps G and H until you have settled on a small set of scenes. 11. Of the scenes, note the dates of those that include the town of Mecca at the NW end of

the Salton Sea. (It will be easier to compare the images if they are close in time.) 12. Return to the Search Criteria and note the Lat/Long of the NW and SE points. 13. Leave the page in place and open a new browser window for the AVIRIS search that

follows.

CEE 6150 Digital Image Processing 3 Lab 3: Image data sources

Select & identify an AVIRIS scene 1. Log in to 2. the AVIRIS web site http://aviris.jpl.nasa.gov/ 3. Navigate to the data page: Select Data > Get AVIRIS data 4. Choose data from 2006 to present http://aviris.jpl.nasa.gov/alt_locator/ 5. Use the locator tool to isolate data from 2013 for the area NE of the Salton Sea. 6. Limit the dates :

Year >= 2013 AND Year <= 2013; Month >= 7 AND Month <= 9

7. Adjust the polygon to outline the area NW of the Salton Sea 8. Select Update Map

Each scene that covers the outlined area will be displayed on the map. The map will zoom out to show the extent of the flight line.

9. Clicking within the shaded area delineating the flight line will bring up a text box describing the data. Clicking on the image name (e.g., f130924t01p00r06) will display a quick look image.

10. Identify the scenes that cover the area just NW of the Salton Sea.

Select & identify an OLI scene The criterion here is to find the OLI scene that is closest to the date of the AVIRIS image.

1. Return to EarthExplorer page used in the Hyperion data search. 2. Under the Data Sets tab, select Landsat CDR > Land Surface Reflectance –L8 OLI/TIRS

You can search for data from more than one system at a time. There is no need to redefine the search area or remove Hyperion from the search list.

3. Adjust the search criteria (map, time range) as necessary to refine the search. 4. You may want to reduce the date range to bracket the AVIRIS dates more closely. The

OLI imagery returns to the same point every two weeks, and the selected area appears in scenes from adjacent orbits. Also, since the TIRS data are included, the nighttime imagery is also included.

5. The black images are nighttime images. 6. Clouds appear as blue-green masses in the daytime images.

Select the combination of images that:

1. Over lap to cover both agriculture and desert. 2. Have minimal or no cloud cover over the area of interest. 3. With a minimum time difference between collection dates.