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VIBRATORS
Vertical vibrators (Figure 1) produce an asymmetric radiation pattern of P-waves and S-waves. Horizontal vibrators produce weak P-waves and robust S-waves.
VIBRATORS
Vertical vibrators (Figure 1) produce an asymmetric radiation pattern of P-waves and S-waves. Horizontal vibrators produce weak P-waves and robust S-waves.
Figure 1: Vibrator base plate
Vibrators are designed in two basic groups: buggymounted and truck-mounted units. The buggy vibrator
(Figure 2) is usually more mobile and causes less damage off-road than a truck-mounted vibrator. Most buggy vibrators are pivoted, or swivel behind the cab, and many can also pivot vertically behind the cab. This maneuverability and flexibility allows for less environmental impact and improved ease of use. On the downside, buggy vibrators must be trucked (Figure 3) and can get stuck in fine sand. The truckmounted vibrator (Figure 4) is more efficient for roadwork and use around more developed areas. The truck-mounted vibrator does not perform as well offroad as a buggy, so vibrator choice is usually dictated by the project logistics.
Sweep Definition
The sweep is defined by
1. Its length
2. Its frequency range
3. Its frequency variation function (up, down, linear, exponential, etc…)
4. Its Amplitude variation function
5. Its initial phase
The need for correlation
The output correlated trace peaks occur at reflection times when the reference sweep lines up with the reflected waveform as shown in fig 6.
