高频共振预探测多脉冲激光测距方法

在无合作目标激光测距中,提出了一种高频共振预探测和多脉冲相关处理对远目标距离进行高精度测量的技术方案.脉冲回波光电流信号经高频共振预探测电路进行放大滤波处理并转换为包含高精度定时特征点的高信噪比的双极性衰减振荡脉冲信号;之后利用多脉冲相关处理构造出的新脉冲函数进一步改善其信噪比.理论计算结果表明:最小可探测光脉冲电流仅为17 nA,与直接探测脉冲方法相比信噪比可提高60倍;在回波光电流脉冲峰值1:10000的动态范围内,走离误差小于0.1 ps.根据此原理研制出了脉冲激光测距仪,仪器在激光发射平均功率约为1 mW时,无合作目标测程大于2000 m,在1.5—300 m范围内测距精度达到±(3 mm+2 ppm),远目标测距精度为±(10 mm+10 ppm).该测距仪系统已用于全站仪产品中.

Multi-pulse laser ranging method for pre-detection with high frequency resonance

Based on the measurement principle of pulse time-of-flight, non-cooperative target ranging technology using a pulsed laser diode (LD) as a light source has received widespread attention in recent years. Using leading edge timing method to directly detect pulses, its measuring range is about a few tens of meters and only a cm-level single-shot accuracy could be reached due to the limitations of its pulse width and eye-safe laser power of the LD, which cannot meet the needs of most applications. Especially, in order to increase its receiver channel bandwidth from hundreds of MHz to even a few GHz to reduce its work error, its distance measurement accuracy and ranging distance are significantly degraded as its signal-to-noise ratio (SNR) decreases. When a target is out of its measuring range, the back diffused laser pulse signal with an SNR of much less than 1 will be too weak to be extracted even with digital correlation processing technology.
In this paper, using a pre-detection with high frequency resonance and multi-pulse correlation processing, a new ranging method to solve long ranging targets with high precision is proposed for the first time. Through the pre-detection circuit with high frequency resonance, a pulsed photocurrent signal is amplified and filtered, and then converted into a bipolar attenuation oscillation signal. Thereafter, its SNR is further improved by a new pulse function constructed through multi-pulse correlation processing. The peak of the new pulse is constant and its zero crossing point is found to be the timing point to calculate the target distance. The method has a better SNR and a high timing accuracy. And the detected ranging distance could be increased over one thousand meters or more. Theoretical calculation results show that the minimum detectable peak current of light pulse is around 17 nA in the method. Comparing with the direct pulse detection method, its SNR can increase 60 times. When a received peak of a photocurrent pulse is within a dynamic range of 1:10000, its work error is less than 0.1 ps. A pulsed laser rangefinder is developed based on the principle. And its average laser emission power is about 1 mW. Its measurement ranging without cooperative target is greater than 2000 m. Its distance measurement accuracy increases up to ± (3 mm+2 ppm) in a range of 1.5-300 m. For a long ranging target, its distance measurement accuracy is ± (10 mm+10 ppm). The rangefinder system is used in a total station product and can be used to measure large-scale engineering structures (such as roads, bridges, dams, tunnels, subways, etc.), building structures and industrial sites.