Zhu Yadan, Liu Jiqiao, Chen Xiao, Zhu Xiaopeng, Bi Decang, Chen Weibiao
Opt Express. 2019 Oct 28;27(22):32679-32699. doi: 10.1364/OE.27.032679.
In this study, a 1.57-µm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was developed for CO measurements. This airborne IPDA LIDAR is integrated with a real-time frequency monitoring system, an integrated sensor for temperature, pressure, and humidity, an inertial navigation system, and a global positioning system. The random errors of the LIDAR system, which are caused by the signal noise, background noise, and detector noise, among other factors, are analyzed for different target reflectivities at a flight altitude of 8 km. After parametric optimization, the signal is unsaturated at high target reflectivity. Further, it can be detected at low target reflectivity by adjusting the detector gain. After the averaging of 148 shots, the relative random error (RRE) was 0.057% for a typical target reflectivity of 0.1 sr. Moreover, the systematic errors caused by the laser pulse energy, linewidth, spectral purity, and frequency drift, as well as the atmospheric parameters related to the flight experiments are also investigated. The relative system error (RSE) was 0.214% as determined based on an analysis of the systematic errors, which are primarily caused by the frequency drift. Two methods are proposed to reduce the RSE caused by the frequency drift. The first is the averaging of 148 shots, which can reduce the RSE to 0.096%. The other method involves calculating the integral weight function (IWF) using real-time frequency. However, this is a time-consuming and computationally intensive process. Hence, look-up tables for the absorption cross-section were created to overcome this issue, resulting in a decrease in the RSE to 0.096%. Using actual aircraft attitude angles, velocity, and position data from flight experiments, the relative errors (REs) in the IWF caused by the uncorrected integral path and Doppler shift were determined to be 0.273% and 0.479%, respectively. However, it was found that corrections to the integral path and Doppler shift based on accurate calculations of the IWF cause the airborne platform to turn in such a way that the REs are eliminated. Hence, this study confirms the validity of system parameters and provides a reference for other researchers who study similar IPDA LIDAR systems. Further, the sensitivity analysis of the airborne IPDA LIDAR system can provide a reference to future data inversions. Moreover, the proposed correction algorithms for the integral path and Doppler shift contribute to more accurate inversion results.
在本研究中，开发了一种用于一氧化碳（CO）测量的1.57微米机载双脉冲积分路径差分吸收（IPDA）光探测与测距（LIDAR）系统。该机载IPDA激光雷达集成了实时频率监测系统、温度、压力和湿度综合传感器、惯性导航系统以及全球定位系统。分析了在8千米飞行高度下，由信号噪声、背景噪声和探测器噪声等因素引起的激光雷达系统随机误差，针对不同目标反射率进行了分析。经过参数优化后，在高目标反射率下信号不饱和。此外，通过调整探测器增益，在低目标反射率下也能进行检测。在对148次测量进行平均后，对于典型目标反射率0.1球面度（sr），相对随机误差（RRE）为0.057%。此外，还研究了由激光脉冲能量、线宽、光谱纯度和频率漂移以及与飞行实验相关的大气参数引起的系统误差。基于对主要由频率漂移引起的系统误差的分析，确定相对系统误差（RSE）为0.214%。提出了两种方法来降低由频率漂移引起的RSE。第一种方法是对148次测量进行平均，可将RSE降低至0.096%。另一种方法是使用实时频率计算积分权重函数（IWF）。然而，这是一个耗时且计算量大的过程。因此，创建了吸收截面查找表来克服这个问题，使RSE降至0.096%。利用飞行实验中的实际飞机姿态角、速度和位置数据，确定未校正积分路径和多普勒频移在IWF中引起的相对误差（RE）分别为0.273%和0.479%。然而，发现基于IWF精确计算对积分路径和多普勒频移进行校正会使机载平台以消除RE的方式转向。因此，本研究证实了系统参数的有效性，并为研究类似IPDA激光雷达系统的其他研究人员提供了参考。此外，机载IPDA激光雷达系统的灵敏度分析可为未来的数据反演提供参考。而且，所提出的积分路径和多普勒频移校正算法有助于获得更准确的反演结果。
