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.

Limitations:

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