Ultrasonic Guided Waves-Based Monitoring of Rail Head: Laboratory and Field Tests

Table 2

Mother wavelet, number of largest wavelet coefficients, and statistical features considered in the rail head algorithm monitoring system.

Mother wavelet #	Mother wavelet	#	# of largest coefficients retained(1)	Feature #	Statistical Feature
a	“db4”	I	6–6	1	RMS_o
b	db7^′	II	6–10	2	ppk_ o
c	db10^′	III	10–6	3	CF_ o
d	“coif4”	IV	10–10	4	RMS_ w
e	“sym5”			5	ppk_ w
f	sym7^′			6	CF_ w
				7	RMS_ r
				8	ppk_ r
				9	CF_ r
				10	Area_ FFT
				11	RMS_FFT

(1)The first number refers to the decomposition level 2 or 4 when the high-frequency bandwidth or the low-frequency bandwidth is considered, respectively. The second number refers to the decomposition level 3 or 5 when the high-frequency bandwidth or the low-frequency bandwidth is considered, respectively.