January 13, 2004
D. M. Fitzgerald, G. A. Zarillo & S. Johnston
Fig. 5. Migration of inlet thalwag at New Pass, Florida (from Irish and Lillycrop, 1997).
whereas higher frequencies yield better resolution. A recent advance in sub-bottom
seismic technology is the frequency swept or Chip system. Chirp technology re-
duces the trade-off between signal range and image resolution. The Chirp system's
frequency sonar system emits a broadband FM source pulse having low frequencies
for depth penetration into the sub-bottom and higher frequencies for high vertical
resolution. The typical Chip data acquisition unit controls all data transmission,
recording and signal processing including analogue to digital conversion, compres-
sion of the FM pulse and spherical divergence correction. The recorded signal is the
output of the correlation filter used for pulse compression and is usually stored in
industry standard SEG-Y format.
A series of hydrophones trailed behind the boat receives the return signal. Simi-
lar to GPR, energy that penetrates the sediment is reflected off changes in lithology