CHIRP Data Processing Methods for Optimal Value in Lake and Reservoir Studies

Acoustic geophysical surveying often precedes sediment coring in studies of extant lakes and reservoirs. Compressed high-intensity radiated pulse (CHIRP) acoustic reflection data acquired in lakes are generally recorded as an amplitude envelope for each trace. This format allows real-time imaging and optimizes on-site planning for sediment coring. However, the amplitude envelope format limits post-processing, so signal-to-noise ratio improvements using typical vendor visualization software are restricted to gain, band-pass filtering, and muting functions. The resultant images often provide a usable representation of the shallow sub-bottom geology, but additional signal processing (e.g., migration, weighted trace mixing, and frequency-space deconvolution) can significantly improve overall image quality and enhance the detection of subtle structural and stratigraphic features. To overcome limitations associated with the amplitude envelope format, we present a methodology to produce a simplified, but representative, simulated reflection amplitude waveform that can be imported into data processing software for the widest range of signal-to-noise enhancements. We provide examples of our workflow from Jackson Lake (Grand Teton National Park, WY), a natural lake that has been converted into a reservoir with complex stratal and structural characteristics. We compare the results of the workflow with actual reflection data and note the benefits of using the true reflection waveform data where possible.