Subbottom Chirp Display and Manipulation
Enable subbottom operation on
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
- 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.
- Program was last actively used about 5 years ago. Code cleanup is
- 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
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
- 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
- Protractor--show in upper left corner of screen.
- Show --how deep to show.
- Options--opens popup menu, based on the number of samples.
- 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.
- Display options (many of these
may no longer do anything)
- Subset: subbottom record
after segmenting, getting a smaller record, which might be easier
to interpret if it is a straight line.
- 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.
- 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
- 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.
|| 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
- 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
- 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
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