© November 2000
Bottom Detection and Re-alignment
Klick to enlarge Figure 1: 4 kHz Parasound echo traces. Due to insufficient heave compensation the bottom first break and later returns show a wavy incoherence. Also crosstalk from a second acoustic system is present, showing as a slanting series of stripes mixed with the Parasound signals. Klick to enlarge Figure 2: 4 kHz Parasound echo traces after time-frequency detection and re-alignment. The time-frequency algorithm can tell crosstalk from genuine signal. Coherency is restored.
After successful detection, break-times along neighboring traces are filtered with a median filter for re-alignment. The overall improvement is best seen in a detail from the same profile. Figures 3 and 4 show examples from the sloping bottom later in the profile. The rather complex sub-bottom structure below the upper turbidite layers is well resolved after re-alignment.
Klick to enlarge Figure 3: Original 4 kHz Parasound echogram suffering from insufficient heave compensation. Klick to enlarge Figure 4: 4 kHz Parasound echogram after re-alignment with the time-frequency detector. Figure 5: Echo from a Parasound record, its time frequency spectrum is shown in figure 6. Klick to enlarge Figure 6: 3-D Sonogram of a Parasound echo. The sonogram was calculated in a frequency band from 2 to 7 kHz, the time axis starts with the first break. Later returns from the sub-bottom sediments have lost energy and shift towards lower frequencies. |