Seismic coupling risk map
Seismic coupling risk map (Source: WesternGeco)
Vibroseis trucks are the most common form of seismic source in land surveys. These trucks move to shot points and the operator lowers the vibrator baseplate to place it in contact with the ground. The entire weight of the truck is then lifted onto this plate. The seismic signal is then sent into the ground by the action of the cylinders which exert force on the baseplate. It is important to maintain good contact with the baseplate and the earth’s surface, this is known as coupling. The quality of the recorded signal depends to a large extent on the baseplates contact with the ground. In addition to good contact, the surface needs to support the weight of the truck on the baseplate at each shot point.
A seismic coupling risk map is an integrated EO product that maps locations/areas that will be potentially a problem for coupling the base plate with the surface. Vibroseis operations are trying to achieve full and firm contact with the ground.
Managing this risk permits maximum vibrator quality data to be achieved in the field. This is monitored by sensors mounted on the shaker and the baseplate. If the baseplate is not coupled with the ground then it is no longer possible to transmit high fidelity vibrations into the ground. On soft ground, if the baseplate cannot be supported, it will break through the surface. This causes the controller to compensate by increasing the signal force which results in increased distortion of the emitted signal.
This integrated product is a cost map that aligns risk associated to each mapped feature mapped. A seismic coupling risk map will help geophysicists understand and plan for areas where the quality of the seismic signal will be impacted. The survey can be adjusted with offset points or infill to maintain the fold required by the client.
EO products such as soft ground mapping, lithology mapping and roughness mapping are the main inputs into the coupling risk map. These products provide a first look at the surface and can therefore help with planning mitigating the risk of point loading.
Known restrictions / limitations
Lifecycle stage and demand
Geographic coverage and demand
Global coverage (with a few restrictions see below). Demand in remote regions is high with exposed non vegetated surfaces best suited.
Input data sources
Optical: VHR1, VHR2, HR1, HR2, MR1
Spatial resolution and coverage
Spatial resolution: 1 m – 90 m pixel size
Minimum Mapping Unit (MMU)
Variable, but a 4 pixel area for Landsat data gives 3.6 km2 MMU
For optical satellite data with 0.5m spatial resolution this can be for example a MMU of 4 m².
Accuracy / constraints
Thematic accuracy: 80-90%
Spatial accuracy: The goal would be one pixel, but depends on reference data
Accuracy assessment approach & quality control measures
Stratified random points sampling approach utilizing in-situ measurements and any available published data or reports. Statistical confusion matrix with user’s and producer’s accuracy as well as kappa statistics for hydrological network and catchment area mapping.
Frequency / timeliness
Observation frequency: Archive data can be used although new acquisition may be a requirement in some situations. The frequency is constrained by client needs, satellite revisit and acquisition, but also processing requirements. Depending on the requirements of the customer the best suitable satellite sensor has to be chosen regarding spatial / spectral resolution as well as revisit frequency.
Timeliness of delivery: Delivery in time with project planning requirements. Archive data can be used to good effect if the prevailing conditions are known and the time of year is accounted for.
Delivery / output format
|Peer Reviewer:||Hatfield Consultants|
Seismic coupling risk map
# of Pages:
Internal – Project consortium and science partners
External – ESA
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