A typical scheme of LDV is shown in the literature.[1] LDV is based on the principle of laser interference, which requires the laser (He-Ne) with good monochromaticity and phase stability. The detection scheme of LDV is optical heterodyne detection, which requires the reference light with an MHz-level frequency shift produced through an acoustic-optic modulator (AOM). As a result, LDV, composed of high-performance phase-stable lasers, interference optics, AOMs, high-power drivers and complex high-frequency modulation and demodulation circuits, is much more delicate and expensive than REAL, which needs only a stable laser pointer, optical lenses and signal amplification circuits.