Comparison of low-frequency data from co-located receivers using frequency dependent least-squares-subtraction scalars
Kevin W. Hall, Gary F. Margrave, Malcolm B. Bertram
Eight-trace shot gathers were created from a subset of the data collected during the Priddis low-frequency comparison test. For this study, we are only considering the 2-10 Hz EnviroVibe shots. The geophone data were decimated to a ten meter spacing to match the other datasets. The southernmost receiver station was dropped from the geophone and accelerometer data, as there was no seismometer to compare to for this station. Sixty seconds of seismometer data were extracted from the continuous data stream based on time of shot, de-biased to remove the resulting (sometimes large) zero Hz component, and re-sampled from 10 ms to 2 ms to match the other data. The resulting datasets were aligned based on cross-correlations, and then compared by filtering the traces with a 1 Hz wide sliding bandpass filter (0.1 Hz increment from 2-10 Hz), and calculating a least-squares-subtraction scalar (LSSS) for each bandpass filter step. In general, the integrated Sercel 428XL/DSU3 data is closest in overall amplitude to the raw Nanometrics/Trillium seismometer data. The Aries/geophone and Ion/VectorSeis data are roughly 108 times smaller than the seismometer data in amplitude. The LSSS depend on amplitude, frequency, phase, source-receiver offset, and quality of sensor placement in or on the ground.