USGS

Venus Mapping White Paper

Open-File Report 95-519


Appendix 1

Calculation of Backscatter Coefficients from Magellan Images Using the MGN_DATA Program

1. Obtain the program by anonymous ftp from ceps.nasm.edu (192.138.170.27). The material is in /pub/venus. The ftp directory contains the source code, mgn_data.f, along with a compiled version made using the static options to allow the code to run on machines that do not have Fortran installed. This program was set up on a Sun Sparc workstation but should be VAX-compatible with some adjustments to the read statements that access the CD-ROM.

2. Compile the program on your machine using [f77 -e -o mgn_data mgn_data.f], or just use the already compiled version if your machine will accept it.

3. Mount a CD-ROM with the desired image product.

5. Using whatever display program you choose, set up one of the framelets such that you can read the (x,y) pixel locations of points within the image.

6. From the CD-ROM directory of the chosen MIDR, run the compiled program in a separate window.

7. The program will ask for (a) a destination file path and name for the output log file, (b) what type of incidence angle profile this image used, (c) whether this is a C-MIDR or F-MIDR, and (d) the name of the framelet label file you want to work with. Version 2 of this program now permits all four DLAP modes to be selected (left, right, stereo, Maxwell).

8. Once it gets the mapping information from the image header, the program allows you to select corner points of boxes within the framelet. It will then report the (latitude, longitude) boundaries of the box, the range of incidence angles, and the mean and standard deviation of all non-zero pixels. The output average echo is in backscatter cross section per unit area (backscatter coefficient) and has had the Muhleman correction taken out. The values in parentheses following the mean echo, in decibels, are the coefficients at plus and minus one standard deviation, also in decibels.

For each box you may also add a one-line annotation to indicate the terrain type on the log file.

A sample run of the program and its output follows.


EXAMPLE OF A SESSION WITH MGN_DATA

/cdrom/c130n045: 3>mgn_data

Name of the data log file (in single quotes)?

'/home/campbell/guide/logfile'

Input label file from a Magellan CD-ROM?

c1f28.lbl

Specify DLAP for this image:

Left-looking: l

Right-looking: r

Cycle 3 Maxwell: m

Stereo: s

l

Is this an F-MIDR or a C-MIDR (c or f)?

c

Upper left (x,y) and lower right (x,y) of box?

248,18,313,82

Description of site for log file (s. quotes)?

'Plains Unit 1'

Box coordinates:

Upper left lat, lon: 30.99926 43.50247

Upper right lat, lon: 30.99926 43.66403

Lower left lat, lon: 30.86304 43.50522

Lower right lat, lon: 30.86304 43.66654

Range of angle across the box: 41.71 41.76

Number of non-zero points in box: 4290

Mean and standard deviation of SAR: 0.0153 0.0039

Mean SAR echo in decibels: -18.140 (-19.397, -17.166)

Would you like another box?

y

Upper left (x,y) and lower right (x,y) of box? 241,269,270,291

Description of site for log file (s. quotes)?

'Bright Lava Flow'

Box coordinates:

Upper left lat, lon: 30.46505 43.49583

Upper right lat, lon: 30.46505 43.56751

Lower left lat, lon: 30.41822 43.49676

Lower right lat, lon: 30.41822 43.56841

Range of angle across the box: 41.92 41.94

Number of non-zero points in box: 690

Mean and standard deviation of SAR: 0.1660 0.0376

Mean SAR echo in decibels: -7.799 ( -8.914, -6.912)

Would you like another box?

y

Upper left (x,y) and lower right (x,y) of box? 383,137,458,188

Description of site for log file (s. quotes)?

'Moderate Lava Flow'

Box coordinates:

Upper left lat, lon: 30.74599 43.84222

Upper right lat, lon: 30.74599 44.02813

Lower left lat, lon: 30.63744 43.84400

Lower right lat, lon: 30.63744 44.02971

Range of angle across the box: 41.81 41.85

Number of non-zero points in box: 3952

Mean and standard deviation of SAR: 0.0758 0.0199

Mean SAR echo in decibels: -11.202 (-12.522, -10.191)

Would you like another box?

N


OUTPUT OF MGN_DATA RUN

Data from Magellan Image Framelet: C1F28.IMG

Part of Magellan Image: C1-MIDR.30N045;201

Pixel scale of image (m): 225.000

Plains Unit

Box pixel boundaries (x1,y1,x2,y2): 248 18 313 82

Box coordinates:

Upper left lat, lon: 30.99926 43.50247

Upper right lat, lon: 30.99926 43.66403

Lower left lat, lon: 30.86304 43.50522

Lower right lat, lon: 30.86304 43.66654

Range of angle across the box: 41.71 41.76

Number of non-zero points in box: 4290

Mean and standard deviation of SAR: 0.0153 0.0039

Mean SAR echo in decibels: -18.140 (-19.397, -17.166)

Bright Lava Flow

Box pixel boundaries (x1,y1,x2,y2): 241 269 270 291

Box coordinates:

Upper left lat, lon: 30.46505 43.49583

Upper right lat, lon: 30.46505 43.56751

Lower left lat, lon: 30.41822 43.49676

Lower right lat, lon: 30.41822 43.56841

Range of angle across the box: 41.92 41.94

Number of non-zero points in box: 690

Mean and standard deviation of SAR: 0.1660 0.0376

Mean SAR echo in decibels: -7.799 ( -8.914, -6.912)

Moderate Lava Flow

Box pixel boundaries (x1,y1,x2,y2): 383 137 458 188

Box coordinates:

Upper left lat, lon: 30.74599 43.84222

Upper right lat, lon: 30.74599 44.02813

Lower left lat, lon: 30.63744 43.84400

Lower right lat, lon: 30.63744 44.02971

Range of angle across the box: 41.81 41.85

Number of non-zero points in box: 3952

Mean and standard deviation of SAR: 0.0758 0.0199

Mean SAR echo in decibels: -11.202 (-12.522, -10.191)