Table 8.

Attributes used in the study and the effects of these attributes.

Group	No	Attributes	Laser effect	Acoustic effect	Equation
Basic statistical properties	1	feat_mean: Mean	Permanent shifts in reflection power	Average power of echoes
	2	feat_std: Standard deviation	Can increase with multiple reflections/complexity	Room modes/fluctuation increases with multiple echoes
	3	feat_var: Variance	Carries the same information as Std on a gridded scale	Conveys same information as std on a squared scale
	4	feat_median: Median: The middle of the ordinal data	Resistant to noise and outliers	Robust center tendency in noisy recordings
	5	feat_mad: Median Absolute Deviation	Resistant to single photon jumps/interference and specular peaks	Resistant to outliers such as sudden impacts
Amplitude/range & energy content	6	feat_min: Minimum values	Deep pits; ghosting/blocking traces	Absorption/cancellation zones
	7	feat_max: Maximum values	Peak scattering; bright spots	Strong early echo/resonance peak
	8	feat_ptp: Peak-to-peak:	Dynamic range; varies with orientation/material	Dynamic range; sensitive to source-target geometry
	9	feat_rms: Root-mean-square	Effective photon count level	Effective acoustic power
	10	feat_energy: Energy	Total power; energy in the scan patch	Total power; secondary echo intensity
Shape/trend	11	feat_slope: Linear slope:	Local increase/decrease trend in the scan	Power Trend within the window (early to late echo)
	12	feat_skew: Skewness	Asymmetric scattering (single dominant reflection)	Asymmetric echo distribution
	13	feat_kurt: Kurtosis	Spiked peak/multi-peak structures	Narrow resonances/sharp peak behavior
Time dependence	14	feat_ac1 Autocorrelation coefficients	Short-scale periodicity; scan pattern	Short delay echo dependence
	15	feat_ac2 Autocorrelation coefficients	Longer short-period effects	Room modes/early-mid echoes
Spectral summaries (Fast Fourier Transform-FFT based)	16	feat_spec_centroid: Spectral center of mass	Energy “center of gravity”; shifts with geometry	Energy shift to HF; material/distance effect
	17	feat_spec_spread: Spectral spread	Bandwidth; scene complexity	Bandwidth; echo richness
	18	feat_spec_entropy: Spectral entropy	Spectral non-uniformity; multiple scattering	Spectral non-uniformity; multiple echoes/scatter
	19	feat_dom_freq_bin: Dominant frequency component	Dominant “scan-frequency” component	Dominant frequency (Hz); position/resonance effect
	20	feat_dom_power: Dominant power	Strength of dominant component	Strength of dominant component
	21	feat_rolloff85_bin: 85% spectral roll-off component	Energy threshold; HF content limit	Energy threshold; limit of reach to HF