Seismic Data Quality
Initial tests on whole shot gathers suggest that the frequency content of the data is better than expected, in line with what was predicted based on pre-cruise source modeling.
Amplitude spectrum for a typical shot gather (streamer two only) is shown above. The highest amplitudes are found within the frequency range from 5 to 80 Hz, but there also appears to significant signal beyond the notch at 120 kHz to frequencies just over 200 Hz.
Plots of shot gathers in t-x domain (below) after filtering using limited, 20 Hz frequency windows further indicate that the high frequency reflection signal is above the background noise level at all recorded frequencies (up to about 210 Hz) and can constructively be used during the imaging process.
Figure shows test of signal frequency content in shot gather 1300 (line 17008P, streamer 2) using limited frequency range windows. Note that reflection and diffraction signal is present in at all frequency ranges up to just over 200 Hz.
Our initial assessment indicates the quality of the recorded data is high. Most of the few noisey channels per streamer appear to have adequate signal to noise ratio to be useable after noise removal, amplitude balancing and frequency conditioning.
Example shot gather (line 1708P, shot 1300, streamer 2) after f-x filtering to remove low frequency swell noise on streamer.
One of the key factors contributing to the quality of a 3D MCS survey is the accurcy of the positioning achived for the sources and receivers. During our survey, contractors from NCS SubSea provided post-processing of the seismic navigation to generate processed U.K.O.O.A. P1/90 files as well as bin coverage maps to assess data fold as the survey progressed. This navigation processing was carried out using Concept Systems Sprint software package and the binning using Concept Systems Reflex. This navigation processing resulted in achieved positional accuracy of better than 3 m for receivers locations, better than 2 m for shot locations, and better than 1 m for the ship position. This level of accuracy is within standard industry specs for comparable programs.