Overview of This Tutorial

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Informations

• Publié par: Vaun
• Nombre de lectures: 50
• Langue: Slovak

Extrait

ENVI Tutorial:
TOPSAR Data and DEM Analysis








Table of Contents
OVERVIEW OF THIS TUTORIAL.....................................................................................................................................3
Background: TOPSAR Data ................................................................................................................................3
DISPLAY AND CONVERT DATA.......4
View TOPSAR Header ........................................................................................................................................4
Load and Display Raw C-Band Image..................................................................................................................4 splay Raw DEM Image......................................................................................................................5
Convert Data Units...............................5
Synthesize P- and L-Band Data...........................................................................................................................7
ANALYZE POLARIMETRIC SAR DATA ..............................................................................................................................8
Display Multi-frequency, Polarimetric SAR Images ................................................................................................8
Examine Polarization Signatures ................................................................................................8
Pedestal Height Image.......................................................................................................................................9
DISPLAY AND ANALYZE DEMS ...................................................................................................................................11
Display the Converted DEM..............................................................................................................................11
Exclude Bad DEM Values..................................................................................................................................11
Build Mask ........................................................................................................................................................................11
Apply Mask..................................................11
X and Y Elevation Profiles ................................................................................................................................12
Arbitrary Elevation Transect .............................................................................................................................13
Density Slice the DEM............................14 Tutorial: TOPSAR Data and DEM Analysis
Overlay Elevation Contours ..............................................................................................................................15
View 3D Perspective and Overlay Image ...........................................................................................................16
Smooth the DEM.............................................................................................................................................17
Generate Topographic Modeling Images...........................................................................................17
Goc Feature Image...............................................................................................................18

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ENVI Tutorial: TOPSAR Data and DEM Analysis Tutorial: TOPSAR Data and DEM Analysis
Overview of This Tutorial
This tutorial uses polarimetric synthetic aperture radar (SAR) data and a digital elevation model (DEM) of Tarrawarra,
Australia, generated from NASA Jet Propulsion Laboratory's (JPL's) Topographic Synthetic Aperture Radar (TOPSAR)
instrument, flown aboard a NASA DC-8 aircraft. The tutorial demonstrates input and display of the TOPSAR data and
display and analysis of the TOPSAR DEM using standard tools in ENVI. For the DEM, these include data input; gray scale
and color-density-sliced display; generation and overlay of elevation contours; use of ENVI’s X, Y, and arbitrary profiles
(transects) to generate terrain profiles; 3D perspective viewing and image overlay; and generation of topographic
modeling and feature images.

Files Used in This Tutorial
CD-ROM: Tutorial Data CD #1
Path: envidata\topsar

Required Files
File Description
ts0218_c.vvi C-Band VV-polarization image, integer format
ts0218_c.cor C-Band correlation image
ts0218_c.dem C-Band DEM image
ts0218_c.inc C-Band incidence angle image
ts0218_l.dat L-Band Stokes matrix data
ts0218_p.dat P-Band Stokes matrix

Background: TOPSAR Data
A full TOPSAR dataset from JPL includes polarimetric (quad-polarized) data for both P- and L-bands and a C-band VV-
polarization image. JPL generates a DEM from SAR interferometry using the C-band antenna. Also provided are the
correlation image and an incidence angle image generated from the C-band data.
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ENVI Tutorial: TOPSAR Data and DEM Analysis Tutorial: TOPSAR Data and DEM Analysis
Display and Convert Data
In this section of the tutorial, you will display TOPSAR data and convert them to physical parameters. Before attempting
to start the program, ensure that ENVI is properly installed as described in the installation guide.
View TOPSAR Header
1. From the ENVI main menu bar, select Radar → Open/Prepare Radar File → View AIRSAR/TOPSAR
Header. An AIRSAR/TOPSAR Input File selection dialog appears.

2. Navigate to envidata\topsar and select ts0218_c.vvi. The AIRSAR File Information dialog appears, listing
information from the embedded AIRSAR Integrated Processor headers.

3. Review the New Header, Parameter Header, and the Calibration Header sections.

4. Repeat Steps 2-3 for the DEM file ts0218_c.dem. View the TOPSAR DEM Header in place of the Calibration
Header.

5. Close the AIRSAR File Information dialog when you are finished.
Load and Display Raw C-Band Image
1. From the ENVI main menu bar, select Radar
→ TOPSAR Tools → Open TOPSAR File. A
file selection dialog appears.

2. Select ts0218_c.vvi and click Open. This
opens and displays the TOPSAR C-Band data
without converting to physical units (sigma
zero), utilizing the embedded TOPSAR header
to get the required file information. This also
loads the image into the Available Bands List.

You could also open this file by selecting
File → Open External File → Radar →
TOPSAR, or by selecting File → Open
Image File, but you have to manually
enter the file parameters with the latter
option.

3. In the Available Bands List, select the Gray
Scale radio button, and click Load Band to
load the image.

4. Examine the geometry and characteristics of
the image. Double-click inside the Image
window to start the Cursor Location/Value
tool. This is a ground-range, C-Band, VV-polarization image scaled to integer format. A scaling factor must be
applied to the data to convert to sigma zero (radar backscatter coefficient).

5. Observe the general magnitude of the pixel values.
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ENVI Tutorial: TOPSAR Data and DEM Analysis Tutorial: TOPSAR Data and DEM Analysis
Load and Display Raw DEM Image
1. From the ENVI main menu bar, select Radar → TOPSAR Tools → Open TOPSAR File. A file selection dialog
appears.

2. Select ts0218_c.dem and click Open. This
opens the TOPSAR DEM data, utilizing the
embedded AIRSAR/TOPSAR header to get the
required file information.

You could also open this file by selecting
File → Open Image File, but you have
to manually enter the file parameters.

3. In the Available Bands List, click Display #1
and select New Display. Click Load Band.

4. Double-click inside the Display #2 Image
window to start the Cursor Location/Value
tool. Observe the general magnitude of the
integer pixel values, which are in units of raw
digital numbers (DNs), as stored in the DEM
file.

5. From a Display group menu bar, select Tools
→ Link → Link Displays. The Link Displays
dialog appears. Click OK to link the two
images. Click in an Image window to toggle
between the two images.
Convert Data Units
1. From the ENVI main menu bar, select Radar → TOPSAR Tools → Convert TOPSAR Data. An Enter TOPSAR
Filename dialog appears.

2. Select ts0218_c.vvi and click Open. A TOPSAR Conversion Parameters dialog appears. ENVI automatically
identifies all of the TOPSAR data based on the TOPSAR file-naming convention. The VV Polarization, Correlation,
Incidence Angle, and DEM images are opened. The C-VV data are automatically converted to sigma zero, and
DEM data are converted to meters based upon values in the TOPSAR headers.

3. Click Spatial Subset and enter 1061 in the Line/To field. This will match the size of the C-band data and DEM
to the P- and L-band data. Click OK.

4. In the Enter Output Filename field of the TOPSAR Conversion Parameters dialog, enter topsar.img and click
OK. Four images are added to the Available Bands List:

VV Polarization