Hydro camp 2008 Sub-bottom Processing


The data was collected with a Knudsen 3.5 kHz chirp echo sounder and stored in the Knudsen KEB format (binary format).  The web site is:  http://www.knudsenengineering.com/html/company/archives2002.htm

The following are the steps in the sub-bottom processing, the command lines are shown in italics:


1.  Convert Knudsen format to OMG Gloria format using command line:

knud2glo \

-omg -VX  -min16_LF 0 -max16_LF 16000  -min16_HF 0 -max16_HF 16000  -out line1 -in line1.keb

The variables are defined as follows:

-omg   specifies format

-VX  version

-min16_LF         specifies where to start for low frequency

-min16_HF        specifies where to start for high frequency

-max16_LF        specifies where to end for low frequency

-max16_HF       specifies where to end for high frequency

-out                     specifies output file name

-in                        specifies input file name

 

2.  View merged data:

swathed line1.merged

The following is an example of the image generated:

 

In this screen you can use the SS (sidescan) function key.  The default image that is shown is the high frequency, by using channel button it will switch to low frequency:





To enhance the image use the log/lin function which uses a logarithmic conversion.  This does not change anything in the file and is strictly for viewing.  You may also look at the bottom pick as selected by the Knudsen for each frequency.  By using the space bar, it allows you to scroll through. 




3.  Covert from 16 bit to 8 bit data:    

k16to8 \

-log -in line1.merged.16_data -out line1.merged.ss_data -min16 100 -max16 16000

The variables are defined as follows:

-log              convert using logarithmic

-in                input line

-out              output line

-min16         minimum

-max16        maximum

At this stage it is a good time to restrict the levels that you are converting.  The following images are of  linear conversions with different minimum and maximum parameters:



Linear conversion with minimum 0 and maximum 16,000



Linear conversion with minimum 0 and maximum 1000



Logarithmic conversion with minimum 100 maximum 5000


4.  Apply "Course Made Good" to file to determine proper position for transducer:

useCMG line1.merged

The CMG command uses the GPS positions to the merged line to give the heading.

5.  Merge navigation file to account for offset:

mergeNav  -delay 0.0 -ahead -2.0 -right 0.0 -below 0.0 line1.merged

Will use above heading to apply correction for the offset of the transducer from the GPS antenna.

6 .  Merge multibeam depth and attitude data:

mergeOtherSonarData \

-in line1.merged -userealTWTT -replace_depth -replace_attitude -draft -0.30 -auto_delay /em3002/*.mergedhttp://start.ubuntu.com/8.04/

This command uses the more correct depths as collected by the multibeam sonar.  The variables are defined as follows:

-in line1.merged                                  input merged file

-userealTWTT                                       use real two way travel time

-replace_depth                                     replaces the Knudsen bottom pick with the multibeam derived bottom pick

-replace_attitude                                 uses multibeam bottom pick in the sub-bottom merged file

-draft -3.0                                             indicates difference between the Knudsen and the multibeam

-auto_delay/em3002/*.merged         corrects for time offsets between the Knudsen and multibeam systems

 

7.  Make plot of profile time vs depth:

makeSeisPlot -mindepth 0 -maxdepth 70 -below -nosam 700 -out kseis/line1.LF -lf -in line1.merged

The variables are defined as follows:

-mindepth 0               minimum depth you want to see in your final profile

-maxdepth70             maximum depth you want to see in your final profile

-below                          indicates that you only want to see the data below the bottom pick

-nosam 700                 indicates the number of samples used

-lf                                  indicates the low frequency transducer

-in line1.merged         sub-bottom merged line


8.  View plot:

jview -seis -initstr 255 0 -autoj line1.LF &

9.  Create file containing boundary of line limits:

getBounds line1.merged

10.  Make blank grid for viewing navigation:

make_blank -boundsof *.merged

11.  Select Projection Area:

jview image.r4 -navlook line1.nav -pickrot


The first step is to identify a 'box' that is oriented along the direction of the sub-bottom line.  This is done using the pickrot option in jview.  As shown in the first image, you can identify the red survey line.  The second image shows the 'bounding' box being manipulate using the arrow keys.  The third image shows the 'bounding' box encapsulating the survey line.
















12.  Make plot of profile projected by position vs depth:

makeSeisPlot \ -nosam 750 -lf -mindepth 0 maxdepth 100 -map Box.header0 -pixel 10  -fill_map_gap \ -first 0 -last 100000 -out line1.map.LF -in  line1.merged

This command line allows the profile to be projected on a vertical plane.   The variables are defined as follows:

-nosam 750                                  indicates the number of samples used

-lf                                                   indicates the low frequency transducer

-mindepth 0 maxdepth 100      minimum and maximum depth of final profile

-map Box.header0

-pixel 10

-fill_map_gap                                attempt to fill any gaps in the data

-first 0

-last 10000                                   first and last options enable you to identify the starting and ending ping in the line

 

13.  View profile plot:

jview -seis -initstr 255 0 -autoj $4.map$3.LF

14.  Convert to gif:

mk_annotated_gif $SUBDIR $LINE_NUMBER

stretchacres -pgm -low 0 -high 255 -invert -in line1.LF -out line1.pgm

convert -flip -rotate 90 line1.pgm line1.gif