Defining Keywords

The SEG-Y Viewer is used to examine SEG-Y files and to specify the location of certain critical keywords during data loading.

Defining keywords is one of the most important steps performed during data loading.  You need to define keywords so that SeisWare can extract crucial information from the headers of  the SEG-Y file.  

How do I define a keyword?

To load data, you need to specify where certain information is kept in the headers of the SEG‑Y file. We call the information that you need "Keywords".

1. Define the keywords required for the line you are loading.
   
   For 2D lines, you must define keywords for:

• Shot Sequence Number (shot point)
• CDP
• Coordinate X
• Coordinate Y

• Line Sequence Number (Inline)
• Trace Sequence Number (Crossline)
• Coordinate X
• Coordinate Y 

• EBCDIC Header:  The EBCDIC header has important information about a line, such as a company name, a line name, processing type and formats, and the Keyword byte offsets.
• Binary Header: Some important settings are here, such as the sample rate of the data.
• Trace Data: The actual seismic data is stored here.
• Trace Header: The Keywords are stored here.

Keywords are stored in the Trace Header Data View, but can be in any of the listed Formats.  Try switching among the file formats to see how the values change. You will usually see the Keywords in integer (32 bit), or one of the IBM or IEEE floating-point formats.

You can see how the Keyword values change when you scroll () through the traces, use the arrows (), or enter a trace number.

Note: The Data View type must be Trace Data or Trace Header before the Trace Number field is active.

2. Once all of the keywords have been defined, you will see displayed in the white box on the right side of the SEG-Y Viewer. Check that they are defined correctly, with appropriate values and decimal places.
   
   
3. From the File menu, select Save Keywords As.  
   
   
4. Enter a Keyword file name that you will remember and click .  SeisWare automatically adds the .kwd extension to the file name.
   
   
5. Close the SEG-Y Viewer.
   

Defining the CDP

The CDP number normally increases by 1 as the trace number increases by 1. As a result, the graph of the CDP Number increases with a constant slope. Scroll through the traces to find the CDP, then graph the value to ensure that the number increases for the entire file.  

1. Click on the CDP and ensure that the cursor is blinking within the number.  
   
   
2. Click the graph icon  at the top of the SEG-Y Viewer. SeisWare opens the Graph Header Word window.
   
   
    
   
   
   
3. Click  to graph all traces in the file. Check that the graph has a constant slope.  Close the SeisWare Graph.  
   
   
4. To define the Keyword, click on the key icon  . SeisWare opens the Add Keyword window.
   
   
   
   
   
   
5. From the drop-down list beside Key Name, select "CDP Number" and click .
   
   

Defining the Shot Sequence Number

To search for the Shot Sequence Number, switch to the Trace Header view, scroll through the traces one by one, and look for a number that increments by 0.5.  Because some formats do not have decimals, the shot sequence might increase by an integer value, for example, 50 or 500.  If you scroll through a few traces and don’t see a number that increments by such an amount, change the file Format and try again. When you identify the shot sequence number, you need to graph it to ensure that the values increment constantly for the entire file.

1. Click on the Shot Sequence Number and ensure that the cursor is blinking within the number.  
   
   
2. Click the graph icon  at the top of the SEG-Y Viewer. SeisWare opens the Graph Header Word window.  
   
   
3. Click  to  graph all traces in the file. Check that the graph has a constant slope.  
   
   
4. Close the SeisWare Graph. 
   
   
5. To define the Keyword, click on the key icon .  SeisWare opens the Add Keyword window.
   
   
   
   
   
   
6. From the drop-down list beside Key Name, select "Shot Sequence Number" and click .
   
   
7. If the Shot Sequence Number is increasing by an integer such as 5, you need to select a scale factor of 0.1 to correct this. In this case, because the shot sequence number does increase by 5, enter a scale factor of 0.1.
   
   

Defining the Line Sequence Number

The Line Sequence Number only changes after you scroll through all traces for the line.  You might have to scroll through many traces before the Line Sequence Number increments by 1.  Scroll through the traces to find the Line Sequence Number, then graph the value to ensure that the number increases for the entire file.  

1. Click on the Line Sequence Number and ensure that the cursor is blinking within the number.  
   
   
2. Click the graph icon  at the top of the SEG-Y Viewer. SeisWare opens the Graph Header Word window.
   
   
    
   
   
   
3. Enter in "2000" in the Last Trace field to limit the number of traces to graph and click . Check that the Line Sequence Number graph resembles a step function with a constant slope.  Each step represents a different line.
   
   
4.  Close the SeisWare Graph.  
   
   
5. To define the Keyword, click on the key icon  . SeisWare opens the Add Keyword window.
   
   
   
   
   
   
6. From the drop-down list beside Key Name, select "Line Sequence Number" and click .
   

Defining the Trace Sequence Number

The Trace Sequence Number increase by 1 until the Line Sequence Number increments, then the Trace Sequence Number drops to its starting point and begins increasing again. Scroll through the traces to find the Trace Sequence Number, then graph the value to ensure that the number increases for the entire file.  

1. Click on the Trace Sequence Number and ensure that the cursor is blinking within the number.
   
   
2. Click the graph icon  at the top of the SEG-Y Viewer. SeisWare opens the Graph Header Word window.
   
   
    
   
   
   
3. Enter in "2000" in the Last Trace field to limit the number of traces to graph and click . Check that the Trace Sequence Number graph resembles a saw tooth.  Every increasing spike represents an increasing trace number within the 3D survey.  
   
   
4. Close the SeisWare Graph.  
   
   
5. To define the Keyword, click on the key icon  . SeisWare opens the Add Keyword window.
   
   
   
   
   
   
6. From the drop-down list beside Key Name, select "Trace Sequence Number" and click .
   
   

Defining the Coordinate X and Coordinate Y

If the data is from Canada the Coordinate X value will have six digits and the Coordinate Y value will have seven digits. These keywords can be found side by side in the SEG-Y viewer.  If you have seven and eight digit numbers, you will need to apply a scale factor of 0.1. The graphs for these Keywords have an increasing or decreasing slope. They are usually linear, although they can have bends if the lines are crooked.

1. Click on the Coordinate X ensure that the cursor is blinking within the number.  
   
   
2. Click the graph icon  at the top of the SEG-Y Viewer. SeisWare opens the Graph Header Word window.  
   
   
3. Click  to  graph all traces in the file. Check the graph. 
• Sample 2D Coordinate X
• Sample 3D Coordinate X
• Sample Coordinate Y
• Sample 3D Coordinate Y
  
4. Close the SeisWare Graph. 
   
   
5. To define the Keyword, click on the key icon .  SeisWare opens the Add Keyword window.
   
   
    
   
   
6. From the drop-down list beside Key Name, select "Coordinate X"  or "Coordinate Y" and click .
   

Also See

• SEG-Y Viewer