即时/准即时u-v覆盖的光学综合孔径成像分析

介绍了即时/准即时u-v覆盖的光学综合孔径成像技术实时/准实时观测的优点,并以LBT为实例进行了成像分析.对LBT采用快速傅里叶变换、卷积与反卷积算法获得系统的点扩展函数(PSF)与光学传递函数(OTF);探讨了全局传递函数及其对成像效果的影响,说明了即时/准即时u-v覆盖成像特性;用实验仿真的方法验证了全局传递函数在满足准即时u-v覆盖成像的要求情况下能够对天体目标进行较好的图像恢复.     

采用多狭缝条纹管实现激光三维成像

为了实现高清晰,高准确的近距离和中距离探测,介绍了一种采用多狭缝条纹管实现激光三维成像的方法.多狭缝条纹管作为成像系统的核心器件,对成像准确起主要影响.通过对成像原理的分析以及条纹管参数之间的关系推导,对多狭缝条纹管的技术指标进行了计算和设计,得出了电子光学系统的主要设计指标.     

Development of a tunable IR lidar system

A differential absorption lidar system (DIAL) based on a continuously tunable optical parametric amplifier (OPA) pumped by a Nd : YAG laser (200 mJ at λ=355 nm) operating at a maximum pulse repetition rate of 100 Hz has been developed. The system provides continuously tunable coherent radiation in the Visible–near IR range (0.4–2.5 μm), allowing to perform DIAL measurements in a spectral region where most of atmospheric constituents and pollutants display absorption lines. The spectral width of the OPA system is line-narrowed by using a master oscillator dye laser as seeder, achieving a linewidth of 0.04 cm⁻¹ (FWHM), a spectral purity larger than 99% and a frequency stability better than 1 pm h⁻¹, with an output energy in the IR of 1–10 mJ. The OPA system was used to perform DIAL measurements in the lower troposphere. Preliminary results in terms of water vapor content and aerosol backscattering profiles are presented and discussed.     

激光云高仪对那曲地区大气边界层高度的探测分析

2014年7月至8月在第三次青藏高原大气科学试验的支持下,分析了夏季那曲地区大气边界层高度日变化特征.采用激光云高仪通过后向散射信号梯度法求得大气边界层高度,将云顶高度判定为边界层高度时,那曲地区对流边界层高度最高可达3800m,在夜间稳定边界层情况下,最低只有40m.采用无线电探空仪数据,利用位温梯度法、相对湿度梯度法求得大气边界层高度.利用云高仪与探空仪同步实验40天得到的有效数据,对后向散射信号梯度法与位温梯度法得到的大气边界层高度的相关性进行分析,相关系数达0.78,标准偏差为738.84m.对8组较为异常量据的再分析发现云高仪在晴空探测大气时信噪比存在一定的不足.对比早、晚测量结果可知,那曲地区大气边界层高度日变化大,是由于该地区地处内陆海拔较高,夏季日照辐射相对平原地区较强,对流和气温强烈的日变化引起大气层结日变化较大.     

微脉冲激光雷达水平探测气溶胶两种反演算法对比与误差分析

大气气溶胶对人类健康、环境和气候系统具有重要的影响。微脉冲激光雷达(MPL)是一种新型的探测大气气溶胶水平分布的有效工具,而消光系数的反演和误差分析是其数据处理的重要内容。为了探测近地面大气气溶胶的水平分布情况,采用分段斜率法和Fernald算法对合肥地区实测MPL水平数据进行了消光系数反演,并将反演结果进行了对比和误差分析。误差分析表明,分段斜率法和Fernald算法的误差分别主要来源于其理论模型和多个假设条件。虽然分段斜率法和Fernald算法应用于大气水平消光系数的反演都仍存在一定的问题,精确度有待提高,但都能在一定程度上反映出气溶胶粒子的时空分布特征,与前向散射能见度仪的测量结果相关性都能达到95%以上,具有一定的可行性。且相对来说,Fernald法更适用于大气非均匀分布情况下消光系数的反演。     

New technique to simulate angular patterns of polarized signals from multiply scattering media in MFOV and CCD lidars

We present a semi-analytical approach to determine angular patterns of a polarized intensity that form lidar signals from multiply scattering media registered by a monostatic multiple-field-of-view receiver or CCD camera for any polarization state of incident light and any analyzer state at a receiver. Multiply scattering media with a highly forward elongated phase functions are considered. The model of lidar signal formation includes the single near-backscattering and small-angle multiple scattering of light. The developed approach allows computation and analysis of polarized images, including the Mueller matrix images, formed by the laser light backscattered by multiply scattering media, for example, from atmospheric clouds, ocean waters, tissue, etc.     

CO2激光成像雷达距离分辨率测距精度的分析与实验研究

分析了脉冲外差体制CO₂激光成像雷达系统的目标距离分辨率、测距精度和误差的主要来源.对于单个光脉冲测距来讲,信噪比(SNR)起伏引起的探测误差、脉冲前沿触发等概率分布以及脉冲建立时间的随机性等是激光脉冲外差测距的主要随机误差,其它随机误差在数量级上可忽略不计.同时利用现有的CO₂激光脉冲外差探测系统,进行了远目标测距对比实验,观测到了2355 m目标脉冲回波信号,并精确测量出CO₂光脉冲飞行的往返时间,该实验数据可用做系统误差的校正和补偿.     

Optical monitoring of volcanic sulphur dioxide emissions—comparison between four different remote-sensing spectroscopic techniques

The emissions of sulphur dioxide from the Italian volcanoes Mt. Etna and Stromboli were studied in ship-borne underpasses of their plumes. Four different optical spectroscopy techniques were used and inter-compared. All techniques utilise the absorption signature of the gas in the wavelength region of around 300 nm. A differential absorption lidar was employed in active gas concentration assessment. In parallel, a differential optical absorption spectroscopy system (DOAS) provided spectrally resolved absorption spectra. In one configuration the DOAS used a vertically looking telescope and the absorption of the sky-light was studied, while a different DOAS implementation utilised the sun disc as the light source in slant-angle, long-path absorption measurements. Parallel measurements with the customary correlation spectroscopy method were also performed. Path length Monte Carlo simulations of the down-welling radiation through the volcanic plume at different sun altitude and azimuth angles have been performed taking into account also the effects of other geometric parameters as the plume height and extension. The results are discussed with special emphasis on systematic effects due to scattering.     

Development of lasers for spaceborne Doppler wind lidar applications

During the course of years, various activities have been carried out at CESI (incorporating now former CISE Innovative Technologies labs) on Doppler wind lidar (DWL) for spaceborne applications. Historically, the first activities were related to the development of a CO₂ laser transmitter for the DWL development with coherent (heterodyne) detection technique. More recently, efforts have been directed to the technology of neodymium solid-state laser transmitter with direct detection (edge technique). Presently, a work in course involves a team of European firms including CESI and is devoted to the breadboarding of a diode-pumped UV laser for DWL application.     

Mie散射激光雷达研究大气边界层特性

基于Mie散射大气激光雷达,应用Klett算法对回波信号进行了反演,得到大气消光系数和后向散射系数。然后,通过对大气后向散射系数曲线进行拟合得到大气边界层混合层高度以及卷夹层厚度等特征参数。对比雷达实测数据与探空气球所测数据,证明二者存在较好相关性。基于实测数据讨论了四川盆地大气边界层特性对气候的影响。