Chirp display and manipulation

Subbottom Chirp Display and Manipulation

Enable subbottom operation on Menu tab of Options menu choice. By default this is turned off. It adds an icon to map window toolbar.

Open a base map
Open subbottom file(s) with button on map window toolbar.
The following windows will be open:
- Graph showing chirp records. This graph will initially show the entire record, and will probably require modification.
- Map display, showing location of subbottom records as you move through the chirp records
- Table display window for each chirp; this database will be created the first time the file opens. This will show the track on the map.

Limitations:

Program was last actively used about 5 years ago. Code cleanup is incomplete.
Does not consider layback of the fish compared to the GPS. When the software was developed, the fish was deployed on a boom beside the vessel, and the offset from the GPS was minimal.
Horizontal scale on the bottom of the display is incorrect. Location information is given
We removed options for two very old formats of subbottom data. Some of the current available opitons geared to those formats might not work

Chirp Graph.

The title bar shows the file name, line length, and the ship's heading in going from left to right along the profile. This assumes the file has a single straight survey line. If it does not, the

To adjust the display, pick parameters, and then pick the redraw options:

Redraw
Gain adjust up or down. Gain is applied to all records equally.
Redraw: refresh the display.
X dupe: spread out the display for short lines
X thinning: shows more of the record on screen.
Y thinning: shows more of the record on screen.
Reverse line: flip the left and right sides of the display.
Protractor--show in upper left corner of screen.
Fence
Show --how deep to show.
Options--opens popup menu, based on the number of samples.
TWTT
Immediate redraw
TVG: time variable gain. The surface returns will have a TVG of 1, the deepest will have the value set here, and there will be a linear gain between them. The correct value depends on attenuation with depth, which depends on the local geology.

Options--popup menu

Display options (many of these may no longer do anything)
Segment
Subset: subbottom record after segmenting, getting a smaller record, which might be easier to interpret if it is a straight line.
Index
Trace
Depth file create a new file, or open an existing file.
Digitize pick depths, or thicknesses.
Number of returns to show: this controls the depth display.

This has not been tested in quite some time. Fence option may do the same thing better.

Digitize Reflections

Start with options on the popup menu
You should save you files frequently, in case this options misbehaves, at least until you are sure that you understand how it works.
You can create a new file, or append to an existing file.
You should create a different file for each category (water depth, specific reflection, specific layer thickness)
Depths will be negative, and thicknesses will be positive.
The file will contain the source file name.

Open Database, Plot on maps, and Color code by z DB field.

TINs (Triangulated irregular networks), select the DBase table, and get a 3D view of the database with the digitized layers. The quality depends on having a number of parallel lines providing input data.

Trace: (may not be working correctly with JSF data)

Select chirp record number

Two graphs:

One shows the values of return intensity, with the two sets of chirp frequencies in different colors
One shows the values of display grayscale with the current gain, with the two sets of chirp frequencies in different colors

Display Options:

Pick frequency range
Pick first and last records. If you do not adjust this, you may see a severely subsampled image; this affects the horizontal resolution.
Top and base depth (m): lets you isolate the part of the record you want to see, and insure you get the best vertical resolution.

Depth from Chirps (single track echosounder).

Files that can be read:

EdgeTech files with a JSF extension. The only ones tested have two floats for each return.

Files no longer read:

Geo-Star Data Format.pdf, a two page document on "SEG-Y FORMAT FOR DIGITAL RECORDS". These have names like "8-28-09.10" which must be renamed to have a "GSDF" extension. The first time you open a GSDF file, the program will crash, but it will open correctly subsequently. The program will not be happy if the GPS data in the files is not correctly set (we have files with only one location repeated for every record). This option has not been tested recently.

Last revision 3/30/2021