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.


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.


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.

Files that can be read:

Files no longer read:

Last revision 3/30/2021