3D ultra shallow seismic imaging of buried pipes using dense receiver array

Unlike imaging of geological structures, direct imaging of ultra shallow subsurface structures relies on the ability to focus non-planar backscattered energy. To that end we have conducted a controlled experiment where dense receiver array (Bachrach and Mukerji, 2001) was used to image buried objects in 3D. Specifically, we have produced and analyzed an image of 6 diameter pipe buried in a depth of ∼1.5m and carried out detailed velocity analysis of scattered wavefield using advanced imaging concepts. The following are our findings: 1. The key factor in successful imaging of shallow-buried small objects is the use of very dense receiver array which enable the capture of energy scattered from the objects through low velocity sand. 2. The ability to utilize conventional processing and imaging algorithms can be related to the good quality of the data. 3. The velocity resolution is very good and within +/- 10m/s. This suggests that monitoring velocity changes around buried object is feasible with standard velocity analysis techniques. 4. Data must be migrated in 3D for proper imaging of backscattered energy. 5. When large contrast in material properties is present, large wavelengths are also backscattered and can be used to improve image resolution.