Making Angle-Angle tables using MFE

Bruce Appelgate

18 March 1999

Here's a cookbook that was used to create angle angle tables using the program MFE:

The images and .doc file are in directory $DP/mfe_tutor

1. Convert MR1 data to tts format:

mr12tts < MR19618601.00 > $RAW/MR19618601.00.tts

2. Start mfe using a dummy mapping function and preexisting attributes:

mfe MR19618601.00.tts -pmf dummymap -smf dummymap \
-attr ew9605.mfe.5000m.attr &

The top wfe window will display the mapping function file (your angle-angle table), and the bottom window will be empty.

See image mfe_01.jpg

3. Check out the acoustic attributes by using the pull-down menus to select

Attributes -> Acoustic

Select a range of pings to operate on. Thirty pings seems to be a good number, and for this example I selected pings 160 - 190.

Reasonable settings for other parameters include:

See image mfe_02.jpg

When pau changing attributes, click on Apply

4. Generate the bathymetry for this ping range by using the pull-down menus to select "Generate"

The bathymetry soundings for each ping will be stacked in the lower window. Also shown are a series of horizontal blue lines, which represent the depth of each ping's bottom detect. In this example, the bottom detects of all the pings are nearly identical, so they appear to be a single blue line in the figure.

See image mfe_03.jpg

5. Now you can make an angle-angle table.

The big assumption here is that the seafloor is flat in the across-track direction. How will you know? By using data from a spot that you *know* is flat, either a priori or a posteriori. Wow, those are impressive words. Use the pull-down menus to select

"Function -> Flatten"

The top window will display a second function that represents the mapping function required to force the bathymetry points be flat (at the depth of the system's bottom detect). The original MF is now displayed in red. The "flattened" file is now active, and displayed in black. In MFE, the active MF is always displayed in black.

When multiple MF files are displayed on the top window, each is identified by color and name in the corener of the top window. See, "original" is red and "flattened" is black.

The bottom window shows the bathymetry points migrated to their new, recalculated common depth. For each ping, this depth is equal to that ping's bottom detect (blue line).

See image mfe_04.jpg

6. The next big step is to filter the flattened MF

In order to do this well you delete any obvious outlying points from the the flattened MF.

Use the pull-down menu to select

"Function -> Delete"

Delete points by moving the mouse over an offending point and clicking on the left mouse button. Click on as many points as you want, and when you're done click on the right mouse button to exit the deletion mode.

To see how the example was edited, see mfe_05.jpg

7. Now its time to do the filtering.

Use the pull-down menu to select

Function -> Filter

This will bring up the filter attributes panel. For 30 pings, I found that good results were obtained using an angle width of 10.0 with an angle overlap of 0.5.

Click on "Filter" when you're set up.

See image mfe_06.jpg

8. The filtered MF will be made active in the upper MFE window, shown in image mfe_07.jpg in black. Note that this MF is also identified in the list of functions in the upper window.

See image mfe_07.jpg

9. The filtered MF may still need to be edited.
Points can be deleted by using

"Function -> Delete"

Points can be added by using

"Function -> Add"

To see how I cleaned up this example, see image mfe_08.jpg

10. Now its time to see how well your filtered MF performs on the range of pings you originally selected. Recalculate the bathymetry using the new MF by selecting

"Generate"

Remeber that the active MF is shown in black in the upper window. The active MF is the one that's used to generate the bathymetry.-- . The active MF is the one that's used to generate the bathymetry. If you want to make a different MF active, select

"Function -> Activate -> function_name"

The newly calculated bathymetry is shown in the bottom panel. If it appears flat, you've done your job.

See image mfe_09.jpg

The next step is to test your new MF on an several data files using btyp. Sometimes an MF appears to be OK in MFE, but doesn't work well universally. In that case you need to select a different range of pings, or perhaps data from a different hour file, and repeat the steps above. Sometimes you get a good MF the first time, sometimes it takes many iterations. Good luck.