SLiP. Source Line Processing

Transcription

1 SLiP Source Line Processing

2 What is SLiP SLiP (Source Line Processing) is Windows based software for computing source positions. SLiP has been specifically written for OBC type seismic surveys. It deals with high dynamics of OBC gun boats that do not tow streamers and can therefore turn very sharply to avoid obstructions. A vessel is generally positioned using a DGPS system. The arrays are positioned using an RGPS system and a range / angle system. Processing parameters In Slip most of the processing setup parameters are read from the p294 header. Observations, parsed from P294 files, are displayed in time series, gated, and filtered using a least squares polynomial of varying order and length. User-defined filtering parameters are also configurable for every individual node, thus providing extended flexibility during processing. CoS position To estimate the CoS (Centre of Source) SLiP employs non-linear parametric least squares adjustment in which the GPS antennae positions are taken as fixed. All sub-arrays for each source are considered to be part of a fixed object rotated either by array CMG, vessel heading or gun tow direction. The gun tow direction is calculated between the tow point on the vessel and the array mean position. Out of the three available headings, the gun tow direction appears to produce the smallest residuals most of the time. To evaluate the quality of solutions, SLiP utilizes standard statistical testing procedures. Many graphs and reports including residuals, error ellipses, variance factor, array offline, sub-array separations etc., are available to determine if solutions are acceptable. The difference between online source positions from Gator INS and SLiP solutions are shown in the graphs. Observations SLiP processes all observations in sequence, allowing operator to take full control over filtering, gating and final solution QC. Array mask, Vessel Speed, SP interval

3 The values are obtained from E records and used to detect possible anomalies which could affect further processing. Water Depth Our Portal Tool software can be used to receive tide + draft with high accuracy using DGPS system output. Gyros & Heading sensors Water depth is shown with tidal curve if selected. A shot depth in an SPS file is the actual water level at the location of the shot at the time of the shot. Depths are measured by an echo sounder sometimes 200 meters away from the actual shot location. Once you have an echo sounder line on each side of a source/receiver line, SLiP can interpolate water depths under source or at a ground station. Headings are displayed as overlay graph and difference graph. Each gyro or heading sensor output can be weighted before it comes into final solution. GPS Together with tide and draft correction SLiP will provide extremely accurate bathymetry. The GPS positions are linearly moved out. There is a straight line drawn between the first and last point and the coordinates are moved/rotated to that line. This is a good representation of reality as it clearly shows any deviations from a straight line.

4 Pair of observations is treated together. If you make an edit on the northing the easting is also automatically edited. GPS systems difference overlay graph is also provided. Gun Arrays A set of graphs is displayed: It is possible to filter, de-spike, and edit each observation, either range or bearing (angle) separately. Network Statistics After initial and user-defined filtering and edits, resulting solution is shown for verification. Tide Table Network Residuals Array Speed Heading Comparison Sub-Array separations Preplot DC and DI differences Network Statistics Final vs E-record comparison As a result of processing, following data sets are created: Source Line SPS & P1/90 Depth E file Each observation can also be retrieved as text file Depth corrected source and receiver SPS files

5 SLiP also makes it possible to insert tide into any SPS file with valid time stamp. System Requirements OS RAM HDD Windows XP, Windows Server 2000 or later 1Gb 10Mb + extra space for P2 files 1Gz and faster CPU Interfaces COM (or COM over USB) Ethernet 10Mb or faster Future Development SLiP is being developed to take advantage of tight integration with SeisLog survey database and bring latest user interface enhancements to a proper use. It is possible to develop a task for your specific requirements.