Lim Hyung-Chul, Park Jong Uk, Choi Mansoo, Park Eunseo, Sung Ki-Pyoung, Jo Jung Hyun
Korea Astronomy and Space Science Institute, Daejeon 34055, Korea.
Sensors (Basel). 2022 Apr 25;22(9):3293. doi: 10.3390/s22093293.
A laser altimeter using code modulation techniques receives a backscattered pulse wider than the transmitted rectangular pulse when scanning a rough or sloped target surface. This leads to degrading the ranging performance in terms of signal-to-noise ratio (SNR) and detection probability. Unlike the pulsed techniques, little work has focused on the pulse broadening effect of the code modulation techniques. In this study, mathematical models were derived to investigate the pulse broadening effect on the ranging performance of a return-to-zero pseudorandom noise (RZPN) laser altimeter. Considering that the impulse response can be approximated by a Gaussian function, the analytical waveform was derived using a new flat-topped multi-Gaussian beam (FMGB) model. The closed-form expressions were also analytically derived for a peak cross-correlation, SNR, and detection probability in terms of the pulse broadening effect. With the use of a three-dimensional model of asteroid Itokawa for practical surface profiles, the analytical expressions were validated by comparing to the results obtained from numerical simulations. It was also demonstrated that the pulse broadening effect dropped down the peak cross-correlation and then deteriorated the ranging performance. These analytical expressions will play an important role in not only designing a laser altimeter using the RZPN code modulation technique but also analyzing its ranging performance.
当扫描粗糙或倾斜的目标表面时，采用码调制技术的激光高度计接收到的后向散射脉冲比发射的矩形脉冲更宽。这会导致在信噪比（SNR）和检测概率方面降低测距性能。与脉冲技术不同，很少有工作关注码调制技术的脉冲展宽效应。在本研究中，推导了数学模型以研究脉冲展宽对归零伪随机噪声（RZPN）激光高度计测距性能的影响。考虑到脉冲响应可以用高斯函数近似，使用新的平顶多高斯光束（FMGB）模型推导了解析波形。还针对脉冲展宽效应，解析推导了峰值互相关、SNR和检测概率的闭式表达式。通过使用糸川小行星的三维模型来模拟实际表面轮廓，将解析表达式与数值模拟结果进行比较，从而对其进行了验证。还证明了脉冲展宽效应降低了峰值互相关，进而恶化了测距性能。这些解析表达式不仅在使用RZPN码调制技术设计激光高度计方面，而且在分析其测距性能方面都将发挥重要作用。
