Introduction to Hyperspectral Data and Analysis Using ENVI - Tutorial of ENVI Software - Completely GIS, GPS, and Remote Sensing Lecture Material - facegis.com
Introduction to Hyperspectral Data and Analysis Using ENVI

Overview of This Tutorial

This tutorial is designed to introduce you to the concepts of Imaging Spectrometry , hyperspectral images , and selected spectral processing basics using ENVI. For this exercise, we will use Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data to familiarize you with spatial and spectral browsing of imaging spectrometer data. We will start with 1995 AVIRIS radiance data for Cuprite, Nevada, USA, provided by Jet Propulsion Laboratory (JPL) and then compare the results of several reflectance calibration procedures. This tutorial is designed to be completed in two to four hours.

Files Used in This Tutorial

You must have the ENVI TUTORIALS & DATA CD-ROM mounted on your system to access the files used by this tutorial, or copy the files to your disk.

The files used in this tutorial are contained in the C95AVSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM.

The files listed below, along with their associated .hdr files, are required to run this exercise. Optional files listed below may also be used if more detailed calibration comparisons are desired. All image data files have been converted to integer format by multiplying the reflectance values by 1000 because of disk space considerations. A value of 1000 therefore represents apparent reflectance of 1.0.

Required Files

CUP95_RD.INT Cuprite AVIRIS radiance data. 400 samples x 350 lines x 50 bands (integer).
CUP95_AT.INT Cuprite ATREM-calibrated apparent reflectance data. 50 bands (integer).
CUP95CAL.SLI Spectral Library of calibration results for selected minerals (integer).
JPL1.SLI JPL Spectral Library in ENVI format.
USGS_MIN.SLI	USGS Spectral Library in ENVI format.

Optional Files

CUP95_FF.INT Cuprite Flat-Field-calibrated apparent reflectance data. 50 bands (Integer).
CUP95_IA.INT	Cuprite Internal Average Relative Reflectance (IARR) data. 50 bands (Integer).
CUP95_EL.INT	Cuprite Empirical Line calibrated apparent reflectance data. 50 bands (Integer).

Background: Imaging Spectrometry

Imaging spectrometers or "hyperspectral sensors" are remote sensing instruments that combine the spatial presentation of an imaging sensor with the analytical capabilities of a spectrometer. They may have up to several hundred narrow spectral bands with spectral resolution on the order of 10 nm or narrower (Goetz et al ., 1985). Imaging Spectrometers produce a complete spectrum for every pixel of the image (Figure 1). Compare this to broad-band multispectral scanners such as Landsat Thematic Mapper (TM), which only has 6 spectral bands and spectral resolution on the order of 100 nm or greater. The end result of the high spectral resolution of imaging spectrometers is that we can identify materials, where with broad-band sensors we could previously only discriminate between materials.

Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

Figure 1: The imaging spectrometer concept; hundreds of spectral images, thousands to millions of individual spectra (from Vane, 1985).


Introduction to Basic ENVI Functionality

This portion of the tutorial is designed to familiarize you with ENVI features that are useful for spectral processing of imaging spectrometer data.

Start ENVI

Before attempting to start the program, ensure that ENVI is properly installed as described in the installation guide.

  • To open ENVI in Unix, enter " envi " at the UNIX command line.
  • To open ENVI from a Windows or Macintosh system, d ouble-click on the ENVI icon.

The ENVI Main Menu appears when the program has successfully loaded and executed.

  1. Select File->Open Image File and navigate to the C95AVSUB subdirectory of the ENVI t utorial data directory .
  2. Choose CUP95_RD.INT as the input file name.

The file contains 50 bands (1.99 - 2.48 mm) of JPL-calibrated AVIRIS radiance for the Cuprite Mining District, Nevada, USA.

The Available Bands List dialog will appear, listing the 50 spectral band names.

Display a Grayscale Image

  1. Use the scroll bar on the right side of the Available Bands List dialog to scroll through the list until Band 193 (2.2008 mm) is displayed.
  2. Click on Band 193 and then on the "Load" button at the bottom of the dialog.

An ENVI image display containing the selected band will appear.

  1. Position the red box outlining the zoom window by clicking the middle mouse button at the desired location in the Main Display window.

The zoom region will be automatically updated.

  1. Change the zoom factor by clicking the right mouse button in the zoom window to zoom up and the left button to zoom down.
  2. Clicking the middle mouse button in the zoom window centers the selected pixel.
  3. The zoom region can also be changed by dragging the red outlining box using the left mouse button.

Display a Color Image

  1. Load a color composite image by clicking on the "RGB Color" toggle button in the Available Bands List.
  2. Click sequentially on Band 183, Band 193, and Band 207 (2.10, 2.20, and 2.35 mm).
  3. Click "New" to start a new display.
  4. Click "Load RGB" at the bottom of the dialog.

The color image will be loaded into the new (second) image display.

Link Two Displays

Images are "linked" to allow simultaneous, identical user action on multiple images. Once linked, moving the zoom box, the scroll box, changing the zoom factor, or resizing any of the image windows causes the same actions to occur in the linked windows.

  1. Place the mouse cursor in the Display #1 Main Image window and click the right mouse button to activate the Display Menu and select Functions->Link->Link Displays.

The Link Displays dialog will appear (Figure 2). Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

  1. Use the arrow toggle buttons to set both displays to "Yes," and select Display #1 as the base image for the link by selecting it from the "Link Size/Position" menu.
  2. Click "OK" to enable the link.
  3. Position the Zoom window for Display #1 by clicking the left mouse button in the red Zoom Window outlining box in the #1 Main Image Display and dragging it to a new location.

Note how the Display #2 Zoom window updates to correspond with the first display.

"Multiple Dynamic Overlays" are available when two or more images are linked, allowing real-time overlay and toggling (flicker) of multiple grayscale or color images. Dynamic overlays are activated automatically when two or more windows are first linked.

  1. After linking, click the left mouse button in either of the linked images to cause a small portion of the second linked image (the overlay) to appear in the first image (the base).
  2. You can make a quick visual comparison of the images by repeatedly clicking and releasing the left mouse button, which causes the overlay area to "flicker."
  3. Change the size of the overlay by pressing the middle mouse button and dragging the corner of the overlay to the desired location.
  4. After trying the different possibilities, turn off dynamic linking in Display 1 by selecting Functions->Link->Dynamic Overlay Off.

Extract Spectral Profiles

ENVI's "Z" profile capabilities provide integrated spectral analysis. You can extract spectra from any multispectral data set including MSS, TM, and higher spectral dimension data such as GEOSCAN (24 bands), GERIS (63 bands), and AVIRIS (224 bands).

  1. Select Functions->Profiles->Z Profile in the Display 1 Main window.

Current Spectrum

The spectrum for the current cursor location will be plotted in a plot window. A vertical line on the plot is used to mark the wavelength position of the currently displayed band. If a color composite image is displayed, three colored lines will appear, one for each displayed band in the band's respective color (red, green, or blue).

  1. Move the cursor position in the Main or Zoom window.

The spectrum will be extracted and plotted for the new location.

  1. Browse the spectral profiles by clicking and holding the middle mouse button in the Zoom indicator box and dragging the box across the image.

The spectrum will be updated as the Zoom indicator box moves. Note that the spectra you are viewing are radiance--not reflectance--spectra, as you are currently working with Cuprite radiance data.

  1. Save spectra for comparison by choosing the appropriate option from the menu bar at the top of the plot window.

Collect Spectra

  1. Select Options->Collect Spectra in the Spectral Profile Window to accumulate spectra in this plot (Figure 3). Select Options->Replace Spectrum to return to the standard spectral browsing mode. Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

Optionally, to collect spectra in another plot window, open a new plot window and save image spectra from the Spectral Profile Window.

  1. Select Options->New Window->Blank to open a new plot window to contain saved image spectra.
  2. Place the mouse cursor to the right of the right-most plot axis in the Z-Profile window and click the right mouse button.

The spectrum name will be displayed to the right of the plot.

  1. Click and hold the left mouse button on the first character of the spectrum name, drag the name to the new plot window, and release the mouse button.
  2. Select a new spectrum from the image by moving the current pixel location in either the Main Display or Zoom window and repeat the drag-and-drop process to build a collection of spectra in the new plot window.
  3. Once you have several plots in the plot window, select Options->Stack Data in the plot window.

The spectra will be offset vertically to allow interpretation.

  1. To change the color and line style of the different spectra, select Edit->Data Parameters in the new plot window.

Each spectrum is listed by name/location in the Data Parameters dialog.

  1. Select a line and change its properties as desired.
  2. When completed, click "Cancel" to close the dialog.
  3. Select File->Cancel to close the plots after completing this section.

Animate the Data

You can "animate" grayscale images to make the spatial occurrence of spectral differences more obvious.

  1. In the Main window of the grayscale image (Display #1), select Functions-> Interactive Analysis->Animation to create a "movie" using the Cuprite AVIRIS data.

The Animation Input Parameters dialog will appear, listing the bands (Figure 4). Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

  1. Choose a subset of the full set of bands for animation.
  2. Click "Clear" in the Animation Input Parameters dialog.
  3. Click either on the check boxes to the left of bands 12 - 31 (20 bands), or enter 12 and 31 in the text boxes next to the "Add Range" button and click on the button to select the spectral bands.
  4. Change the "Window Size" to 200 x 175 to reduce the size of the image to be animated (and thus increase the speed of the animation).
  5. Click "OK" to return to the Animation Input Parameters dialog.
  6. Click "OK" again to start the animation loading process.

The Animation window and the Animation Controls dialog will appear. The selected bands are loaded individually into the Animation widow. A status bar appears as each image is processed.

  • Cancel the animation in progress at any time by clicking "Cancel" in the status window.

Once all of the selected images have been loaded, the animation will start automatically. Selected bands are displayed sequentially.

 

 

 

The Animation Controls (Figure 5) are used to specify the animation characteristics.

  • The animation speed is varied from 0 to 100 using the slider bar labeled "Animation Speed." Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com
  • The "Update On/Off" button toggles the real-time Frame Number slider bar and display of the frame number. Toggling off this feature and setting the Animation Speed to 100 provides maximum animation performance.
  • Click on the "<-" button to display the animation from highest frame number to lowest.
  • Click on the "->" button to display the animation from lowest frame number to highest.
  • Click on the ">-<" button to allow the animation to proceed sequentially from low to high frame and back.
  • Click on the "-" button to pause the animation.
  • When paused, click and drag the slider labeled "Frame Number" to manually select the band to display.
  • Choose the "Cancel" button to end the animation.

Working With Cuprite Radiance Data

Continue this exercise using the images displayed in the first section.

  1. If you have quit ENVI and IDL, restart ENVI and select File->Open Image File.
  2. Navigate to the C95AVSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM. Choose CUP95_RD.INT as the input file name.

Load AVIRIS Radiance Data

  1. If you don't already have this image displayed, load a color composite image by clicking on the "RGB Color" toggle button in the Available Bands List.
  2. Click sequentially on Band 183, Band 193, and Band 207 and then "Load RGB" at the bottom of the dialog.

The color image will be loaded into the current image display.

Extract Radiance Spectra

To extract selected image radiance spectra for specific targets in the AVIRIS radiance data.

  1. In the Main Display window, select Functions->Interactive Analysis->Pixel Locator.
  2. Position the zoom window over Stonewall Playa, centered around the pixel at sample 590, line 570 by entering these pixel coordinates in the Pixel Locator and clicking "Apply".
  3. Extract the radiance spectrum for this location using the Z-Profile function and save in a new plot window.
  4. Extract radiance spectra for the following locations and load into the same plot window for comparison (Figure 6).
  5. Location Name Sample

    (with offset)

    Line

    (with offset)

    Stonewall Playa 590 570
    Varnished Tuff 435 555
    Silica Cap 494 514
    Opalite Zone with Alunite 531 541
    Strongly Argillized Zone with Kaolinite 502 589
    Buddingtonite Zone 448 505
    Calcite 260 613
  6. Change the colors of the individual plots if necessary by selecting Edit-> Data Parameters and making the appropriate changes in the subsequent dialog. Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

Compare the Radiance Spectra

Note how similar the radiance spectra appear. The overall shape of the spectra is caused by the typical combined solar/atmospheric response.

  • To offset data for comparison of spectral features, select Options->Stack Data in the ENVI Plot Window.

Note small absorption features (minima) near 2.2 micrometers that may be attributable to surface mineralogy.

Load Spectral Library Reflectance Spectra

Now compare apparent reflectance spectra from the image to selected library reflectance spectra.

  1. Select Spectral Tools->Spectral Libraries->Spectral Library Viewer.
  2. When the Spectral Library Input File dialog appears, click "Open New File" and select JPL1.SLI from the list.
  3. Click "OK".

JPL1.SLI will appear in the "Select Input File" field of the dialog.

  1. Click on the file name and click "OK" to open the Spectral Library Viewer dialog (Figure 7).
  2. Plot the following spectra in the Spectral Library Viewer window by clicking on the appropriate mineral name in the list of spectra:Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com
  3. ALUNITE SO-4A
  4. BUDDINGTONITE FELDS TS-11A
  5. CALCITE C-3D
  6. KAOLINITE WELL ORDERED PS-1A
  7. If desired, change the X-Axis scale by choosing Plot Parameters from the Edit menu and entering the values 2.0 and 2.5 for the range.

This will allow direct visual comparison of radiance (Figure 6) and reflectance (Figure 8), though the Y-axes will not have the same scale.

  1. Click "Cancel" to close the Plot Parameters dialog.

Compare Image and Library Spectra

  • Visually compare and contrast the corresponding AVIRIS radiance spectra with the laboratory measurements for alunite, buddingtonite, calcite, and kaolinite.

Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

Note how difficult it is to visually identify the minerals by comparing features in the radiance spectra to absorption features shown in the laboratory spectra.

Note the effect of the superimposed convex-upward solar-atmospheric signature in the AVIRIS radiance data on visual identification.

Close the Windows

  • When you are finished with this section, close all of the plot windows by choosing Basic Tools ->Display Controls ->Close All Plot Windows from the ENVI Main Menu.

Comparison of Radiance and ATREM Reflectance

In this portion of the tutorial you will extract selected image radiance spectra and compare them to ATREM apparent reflectance spectra for specific targets in the AVIRIS radiance data.

Background: ATREM Calibration

The ATmospheric REMoval Program (ATREM) is a radiative transfer model-based technique for deriving scaled surface reflectance from AVIRIS data without a priori knowledge of surface characteristics (Gao and Goetz, 1990, CSES, 1992). It utilizes the 0.94 and 1.1 micrometer water vapor bands to calculate water vapor on a pixel-by-pixel basis from the AVIRIS data, the solar irradiance curve above the atmosphere, and transmittance spectra for each of the atmospheric gases CO2, O3, N2O, CO, CH4, and O2. At the time this tutorial was released, ATREM ran only on UNIX hardware. It can be obtained via anonymous ftp from cses.colorado.edu or by contacting the Center for the Study of Earth from Space at 303-492-5086. The ATREM-calibrated data used for this tutorial were reduced to apparent reflectance using ATREM 1.3.1.

  • ATREM is not included as part of ENVI, but is publicly available. The other calibration methods examined in this tutorial and described here are implemented within ENVI.

Continue or Restart ENVI

Continue this exercise using the images displayed in the first section.

  1. If you have quit ENVI and IDL, restart ENVI and select File->Open Image File and navigate to the C95AVSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM.
  2. Choose CUP95_RD.INT as the input file name.

Load Radiance Data and Start the Z Profiler

  1. If not already loaded, load a color composite image by clicking on the "RGB Color" toggle button in the Available Bands List.
  2. Click sequentially on Band 183, Band 193, and Band 207.
  3. Click "Load RGB" at the bottom of the dialog.

The color image will be loaded into the current image display.

  1. Extract the radiance spectrum by selecting Functions->Profiles->Z Profile in the Main display.
  2. Move the Z-Profile window to the bottom of the screen for easy access.

Load ATREM Apparent Reflectance Data and Start the Z Profiler

Now open a second AVIRIS data set.

  1. Select File->Open Image File and choose CUP95_AT.INT as the second input file name.

This is 50 bands (1.99 - 2.48 mm) of AVIRIS data calibrated to apparent reflectance using the atmospheric model "ATREM" to process the AVIRIS radiance data. The 50 band names will be added to the Available Bands List.

  1. Use the scroll bar on the right side of the Available Bands List dialog to scroll through the list until Band 193 of CUP95_AT.INT is listed.
  2. Click on the "gray scale" toggle button and select band 193.
  3. Click "New" and then "Load" to start a second ENVI image display and load the selected band.
  4. Extract the radiance spectrum by selecting Functions->Profiles->Z Profile in the Main window.
  5. Move the Z-Profile window to the bottom of the screen next to the Z-Profile from the radiance data for easy comparison.

Link Images and Compare Spectra

  1. Link the two AVIRIS images together by selecting Functions->Link from the #1 Display Main window and clicking "OK" in the subsequent Link Displays dialog.
  2. Now turn the dynamic overlay off in Display #1 by selecting Functions->Link->Dynamic Overlay Off.
  3. Once the images are linked and the overlay is turned off, positioning the current pixel in one image (either by clicking the center mouse button in the image, dragging the zoom indicator box using the left mouse button, or by using the Pixel Locator) will also position the cursor in the second image.

The Z profiles for both images will change to show the radiance and apparent reflectance spectra at the current location.

  1. Position the zoom window over Stonewall Playa, centered around the pixel at sample 590, line 570 (use the Pixel Locator dialog found in the Interactive Analysis cascading menu under the Functions menu).

Visually compare both radiance and apparent reflectance spectrum for this location using the two Z-Profiles.

  • If you wish, save the radiance spectrum in one new plot window and the reflectance spectrum in a second new plot window.
  • Use the middle mouse button to the left of the Y-axis to scale spectra to fit in the window.
  • Now extract radiance and apparent reflectance spectra for the following locations and visually compare.
  • Location Name Sample

    (with offset)

    Line

    (with offset)

    Stonewall Playa 590 570
    Varnished Tuff 435 555
    Silica Cap 494 514
    Opalite Zone with Alunite 531 541
    Strongly Argillized Zone with Kaolinite 502 589
    Buddingtonite Zone 448 505
    Calcite 260 613
  • Select Options->Stack Data to offset data vertically for comparison.
  • If you wish, load the corresponding spectral library spectra into the apparent reflectance plot window for direct comparison of image apparent reflectance spectra (Figure 9) with laboratory spectra.

Close the Windows

  • When you are finished with this section, close all of the plot windows by choosing Basic Tools->Display Controls->Close All Plot Windows.
  • Close all of the displays by choosing Basic Tools ->Display Controls ->Close all Displays.

Compare Different Calibrations

Background: Calibration

This section of the tutorial compares several image apparent reflectance spectra. You will use a spectral library of apparent reflectance spectra generated using ENVI's "Flat Field Calibration," "Internal Average Relative Reflectance (IARR) Calibration," and "Empirical Line Calibration" functions to compare the characteristics of the various calibration methodologies. The calibration techniques used are briefly described below.

Flat Field CalibrationIntroduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

The "Flat Field Calibration" technique is used to normalize images to an area of known "flat" reflectance (Goetz and Srivastava, 1985; Roberts et al. , 1986). The method requires that you locate a large, spectrally flat, spectrally uniform area in the AVIRIS data, usually defined as a Region of Interest (ROI). The radiance spectrum from this area is assumed to be composed of primarily atmospheric effects and the solar spectrum. The average AVIRIS radiance spectrum from the ROI is used as the reference spectrum, which is then divided into the spectrum at each pixel of the image. The result is apparent reflectance data that can be compared with laboratory spectra.

Internal Average Relative Reflectance (IARR)

The IARR calibration technique is used to normalize images to a scene average spectrum. This is particularly effective for reducing imaging spectrometer data to "relative reflectance" in an area where no ground measurements exist and little is known about the scene (Kruse et al. , 1985; Kruse, 1988). It works best for arid areas with no vegetation. The IARR calibration is performed by calculating an average spectrum for the entire AVIRIS scene and using this as the reference spectrum. Apparent reflectance is calculated for each pixel of the image by dividing the reference spectrum into the spectrum for each pixel.

Empirical Line Calibration

The Empirical Line calibration technique is used to force image data to match selected field reflectance spectra (Roberts et al. , 1985; Conel et al. , 1987; Kruse et al. , 1990). This method requires ground measurements and/or knowledge. Two or more ground targets are identified and reflectance is measured in the field. Usually the targets consist of at least one light and one dark area. The same two targets are identified in the AVIRIS images and average spectra are extracted for Regions of Interest. A linear regression is calculated between the field reflectance spectra and the image radiance spectra to determine a linear transform from radiance to reflectance for each band of the AVIRIS data set. Gains and offsets calculated in the regression are applied to the radiance spectra for each pixel to produce apparent reflectance on a pixel-by-pixel basis.

Continue or Restart ENVI and Select Spectral Library of Calibration Results Spectra

  1. If you have quit ENVI and IDL, restart ENVI and select Spectral Tools->Spectral Libraries->Spectral Library Viewer.

The Spectral Library Input File dialog will appear to allow selection of a spectral library.

  1. Click "Open New File" at the bottom center of the dialog to start a standard file selection dialog.
  2. Navigate to the C95AVSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM, and select the file CUP95CAL.SLI .

This is the spectral library containing the results from the various calibration methods.

  1. In the Spectral Library Input File dialog, select the open library file name and click "OK".

The Spectral Library Viewer will appear with a list of the calibrated spectra (Figure 10).

Introduction to Hyperspectral Data and Analysis Using ENVI - facegis.comIntroduction to Hyperspectral Data and Analysis Using ENVI - facegis.com

Select Calibrated Spectra from Spectral Library

  1. Select the ATREM, Flat Field, IARR, and Empirical Line calibrated spectra for the mineral Alunite by clicking on the appropriate check boxes next to the names in the list.

The spectra will be plotted in a Spectral Library Viewer plot (Figure 11). Visually compare the various calibrations and note and compare their characteristics.

  1. Attempt to explain some of the differences in terms of the calibration methodology used (see the brief descriptions above of the various methods).
  2. When finished, select Options->Clear Plots in the menu bar at the top of the Spectral Library Viewer to clear the spectra.

Compare Calibrated Spectra

  • Repeat the procedure for the minerals kaolinite, buddingtonite, calcite, and silica.

What general conclusions can you draw about the quality of the different calibration procedures?

  • You can also compare the laboratory spectra for these minerals to the AVIRIS spectra by opening the JPL1.SLI or the USGS_MIN.SLI spectral libraries, plotting the corresponding spectra, and dragging and dropping into the Spectral Library Viewer plot for direct comparison.

Optional: Browse Calibrated Data Files

The calibrated data files for all of the different calibrations are available for spectral browsing if desired. All files have been converted to integer format by multiplying the reflectance values by 1000 because of disk space considerations. Values of 1000 in the data indicate apparent reflectances of 1.0.

  1. Open and load the files listed in the table below if desired.
  2. File Type File Name
    ATREM CUP95_AT.INT
    Flat Field CUP95_FF.INT
    IARR CUP95_IA.INT
    Emp. Line CUP95_EL.INT
  3. Use the Z-profiling and multiple linked images to compare apparent reflectance spectra for specific areas of interest.
  4. After comparison of all of the calibration methods for a variety of minerals, which calibration method(s) best reproduce(s) the laboratory spectra for all minerals? Is there one best calibration method

Exit ENVI

  • When you have finished your ENVI session, click "Quit" or "Exit" on the ENVI Main Menu, then type exit at the IDL command prompt.

If you are using ENVI RT, quitting ENVI will take you back to your operating system.


References

Conel, J. E., Green, R. O., Vane, G., Bruegge, C. J., Alley, R. E., and Curtiss, B., J., 1987, Airborne imaging spectrometer-2: radiometric spectral characteristics and comparison of ways to compensate for the atmosphere: in Proceedings, SPIE, v. 834, p. 140 - 157.

CSES (Center for the Study of Earth from Space), 1992, ATmospheric REMoval Program (ATREM), version 1.1, University of Colorado, Boulder, 24 p.

Gao, B. C., and Goetz, A. F. H., 1990, Column atmospheric water vapor and vegetation liquid water retrievals from airborne imaging spectrometer data: Journal of Geophysical Research, v. 95, no. D4, p. 3549-3564.

Goetz, A. F. H., Vane, G., Solomon, J. E., and Rock, B. N., 1985, Imaging spectrometry for Earth remote sensing: Science, v. 211, p. 1147 - 1153.

Goetz, A. F. H., and Srivastava, V., 1985, Mineralogical mapping in the Cuprite Mining District, Nevada: in Proceedings of the Airborne Imaging Spectrometer Data Analysis Workshop, JPL Publication 85-41, Jet Propulsion Laboratory, Pasadena, CA, p. 22-29.

Kruse F. A., Raines, G. l., and Watson, K., 1985, Analytical techniques for extracting geologic information from multichannel airborne spectroradiometer and airborne imaging spectrometer data: in Proceedings, 4th Thematic Conference on Remote Sensing for Exploration Geology, Environmental Research Institute of Michigan (ERIM), Ann Arbor, p. 309 - 324.

Kruse, F. A., 1988, use of Airborne Imaging Spectrometer data to map minerals associated with hydrothermally altered rocks in the northern Grapevine Mountains, Nevada and California: Remote Sensing of Environment, v. 24, no. 1, p. 31 - 51.

Kruse, F. A., Kierein-Young, K. S., and Boardman, J. W., 1990, Mineral mapping at Cuprite, Nevada with a 63 channel imaging spectrometer: Photogrammetric Engineering and Remote Sensing, v. 56, no. 1, p. 83-92.

Roberts, D. A., Yamaguchi, Y., and Lyon, R. J. P., 1985, Calibration of Airborne Imaging Spectrometer data to percent reflectance using field measurements: in Proceedings, Nineteenth International Symposium on Remote Sensing of Environment, Ann Arbor, MI, October 21-25, 1985.

Roberts, D. A., Yamaguchi, Y., and Lyon, R. J. P., 1986, Comparison of various techniques for calibration of AIS data: in Proceedings, 2nd AIS workshop, JPL Publication 86-35, Jet Propulsion Laboratory, Pasadena, CA, p. 21-30.

Vane, Gregg, and Goetz, 1985, Introduction to the proceedings of the Airborne Imaging Spectrometer (AIS) data analysis workshop: in Proceedings of the Airborne Imaging Spectrometer Data Analysis Workshop, JPL Publication 85-41, Jet Propulsion Laboratory, Pasadena, CA p. 1 - 21.

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