“…The interferometry methods, including Fabry-Perot cavities and Mach-Zehnder interferometers, have complicated structures and high precision fabrication requirements [ 9 , 10 , 11 ]. In the correlation method, the traditional cross-correlation (TCC) is often used to process the output signals of two identical sensors in the measured region [ 12 , 13 , 14 ], which provides non-contact measurements with low cost for monitoring gas-solid and solid-liquid flows [ 15 , 16 , 17 , 18 ]. The image matching method, in which a high-speed camera captures a series of instantaneous images to calculate velocity, also belongs to the correlation methods [ 19 , 20 , 21 , 22 ].…”