Sparse Frequencies Data Inversion: an Application to a Near Surface Experiment

With an objective to invert for the subsurface velocity in the near surface rather than developing an image, we substitute the commonly used broadband acquisition scenario with a novel narrow band acquisition at coarse shot locations. We conduct the acquisition of narrow band seismic data, with an effect of 3 simultaneous sources vibrating at different bands (14-15 Hz, 24-25 Hz, and 49-50 Hz) of the frequency spectrum. The separation of the shot gathers corresponding to the simultaneous sources becomes natural as the shots fall in different bands of the frequency spectrum. The narrow band acquisition allows us to inject more energy of these frequencies using the same conventional vibrator sweep time (6 seconds). We mute regions of low signal-to-noise ratio, and then insert the data into a frequency domain waveform inversion algorithm. The inverted model down to 250 meters depth showed structure corresponding to a low velocity zone at around 80 meter depth. For comparison a conventional full sweep acquisition (30-170 Hz) at a dense shot spacing we recorded. We migrated this conventional dataset using the inverted model. The agreement between the inverted model and the image, extracted from the two independent datasets, supports the accuracy of the inverted model.