firstBreak: Time of first wave break

In emanuelhuber/RGPR: Ground-penetrating radar (GPR) data visualisation, processing and delineation

Time of first wave break

Description

Pick the time of the first wave break in each trace (trace-by-trace function).

Usage

## S4 method for signature 'GPR'
firstBreak(
  x,
  method = c("coppens", "threshold", "MER"),
  thr = NULL,
  w = NULL,
  ns = NULL,
  bet = NULL,
  shorten = TRUE
)

Arguments

x	[GPR class] An object of the class GPR
method	[character(1)] Method to be applied (either coppens, threshold or MER). "coppens" corresponds to the modified Coppens method, "threshold" to the threshold method, and "MER" to the modified energy ratio method.
thr	[numeric(1)] Threshold for the signal amplitude (in %) at which time zero is picked (only for the threshold method). thr ranges between 0 (0%) and 1 (100%).
w	[numeric(1)] Length of the short-term leading window in unit of time (only for method = "coppens" or method = "MER"). Recommended value: about one period of the first-arrival waveform.
ns	[numeric(1)] Length of the edge preserving smoothing window in unit of time (only for method = "coppens"). Recommended value: between one and two signal periods. When ns = NULL the value of ns is set to 1.5 * w.
bet	[numeric(1)] Stabilisation constant (only for method = "coppens"). Not critical. When bet = NULL the value of bet is set to 20% of the maximal signal amplitude.
shorten	[logical(1)] If TRUE, each trace is shortened by removing the samples that are 2 \times w after the maximum value (only for method = "coppens" or method = "MER"). You may set shorten = FALSE if the first wave break occurs after the maximum absolute amplitude time.

Details

The Modified Coppens's method (coppens) computes the energy ratio between a long term window (with increasing length) and a short-term leading window (fixed length). Edge-preserving smoothing is then applied and the first wave break is assigned to the sample in which the derivative of the output is largest.

The modified energy ratio method (MER) computes the energy ratio between a preceding and trailing windows of equal length. The energy ratio is then multiplied by the absolute values of the trace and the output to the power of three is returned.

In the threshold method ("threshold"), the sample before the first sample that is larger than the threshold times the maximum absolute amplitude is picked. Then the time of the first wave break is linearly interpolated between these two samples.

Value

[numeric(n)] The time of the first wave break for every traces in unit of time (n = ncol(x) = number of traces).

References

Modified Coppens method

Sabbione J.I. and Velis D. (2010) Automatic first-breaks picking: New strategies and algorithms. Geophysics, 75(4): 67-76.

Modified Energy Ratio (MER) method

Han L., Wong J., and John C. (2010) Time picking on noisy microseismograms. In: Proceedings of the GeoCanada 2010 Convention - Working with the Earth, Calgary, AB, Canada, p. 4

#' @examples data("frenkeLine00") fb <- firstbreak(frenkeLine00, w = 10) plot(seq_along(frenkeLine00), fb)

See Also

firstBreakToTime0 to convert time of first wave break into time-zero; time0 and setTime0 to set time-zero; estimateTime0 to estimate first wave break, convert it to time-zero and set time zero (all in one step); time0Cor to shift the traces such that they start at time-zero.

emanuelhuber/RGPR documentation built on May 13, 2024, 9:31 p.m.