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Office Based QC/First Lines QC (FLQC) Services
With effective communication systems now
available on many seismic crews and vessels, it is often feasible to transfer
data from the field directly to an office-based environment where a detailed QC
can be carried out.
WTW is able to offer office-based QC of
a subset of the full dataset, or, where file sizes are not too large, the whole
dataset as work progresses, via transfer of data to WTW’s ftp site. Clients are
allocated a secure password protected folder area for upload of data. For large
files, WTW can provide a compression utility which will typically compress (losslessly)
UKOoA P1 data by a factor of 80-100 times, as opposed to the 10-15 times
achievable using standard compression utilities.
Office-based QC services are useful for
First Lines QC (FLQC) where data for the first 3-5 lines acquired on the survey
are uploaded as they become available, thoroughly checked out and a report sent
to the client/ field crew usually within 24 hours. This may be followed up by
QC of additional sample lines as the survey progresses.
A typical FLQC scenario would consist
of:
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P2 compliance checks using Quest’s PXCheck utility
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P1 compliance checks using Quest’s PXCheck utility
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P1 and P2 data inspection
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WTW processing and QC of the sample lines, with QC plots
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Reverse engineering of selected observation data from contractor P1 files
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Comparison of WTW processed data and contractor data via comparison plots
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Analysis of differences
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Report of results
Typical “Conclusion” section from an
FLQC report:
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The port outer streamer was towing around 12
metres further forward than the other streamers for all lines checked.
Presumably this was known on board and was a function of the towing mechanics?
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rGPS range data for all lines checked exhibited
spikes and jumps, causing some difficulty from time to time in optimal
positioning of sources. On some lines the situation was exacerbated by
malfunctioning source acoustic transponders.
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Reverse-engineered rGPS range data to sources
for all lines checked exhibited bias with respect to raw, filtered and
WTW-finalised data. The biases were consistent in size with the Contractor not
having used slant-range correction from rGPS vessel antennae to float antennae.
rGPS
range offsets seen during an FLQC project. Contractor most likely did not apply
slant-range correction.
Comparison examples between WTW-processed
data and Contractor P1 data, in-line/cross line.
FLQC methodology can be extended to the whole dataset, of
required, with detailed office-based QC being carried out either during
acquisition or post-mission, as required.
WTW and Associates is a member of the
IAGC
and is registered with
FPAL.
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