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3.) The Tx antenna is placed in the back part of the unit (between main antenna and wheel
connectors) and Rx antenna is placed in the front part of the unit (between main antenna
connector and unit noose);
4.) The Tx antenna of the first unit (immovable) and Rx antenna of the second unit
(moveable) are used for CDP method;
5.) Here and below the CDP result graph is called as Hodograph and looks like on Fig.
14.2;
6.) The immovable unit direction is opposite to the Hodograph direction (unit noose
backward, unit back ahead), but moveable unit direction coincides to Hodograph direction;
7.) Hodograph starting point is the Tx antenna position of immovable unit;
8.) Here and below the distance between the Tx antenna of immovable unit and the Rx
antenna of moveable unit is called starting offset;
9.) The stepped mode is used for the data acquisition in CDP method;
10.) The moveable unit is shifting for a fixed step size (10-20 cm), one acquired trace =
one step;
11.) The total Hodograph distance has to be 2 times greater than measuring depth;
12.) The Hodograph profile distance has to be entered to profiles settings as Length of
profile, where “From” value is equal to starting offset and “To” value is distance between
starting point (Tx antenna position of immovable unit) and the Rx antenna of moveable
unit (or number of steps multiplied by step size plus starting offset).
When antennas are spaced apart, reflected signal amplitudes drop down considerably;
therefore it is advisable to specify in
Output parameters
Menu
/
Normalizing factor
/
Entire trace
option.
Fig. 16.2. Type profile shot using Common Depth Point technique.
Three signals are clearly visible on the provided profile, namely:
1 – Air wave path signal. Always appears as an inclined straight line.
2 – Signal path reflected from the first layer interface.
3 – Signal path refracted at the first layer interface and reflected from the
second layer interface.
Important!
After you finished sounding and saved the file, be sure to enter the initial
and final antenna spacing in
Output parameters
.
