Lidar effective multiple-scattering coefficients in cirrus clouds

We delimit a regime, valid for most ground-based lidar probings of cirrus clouds, in which the field-of-view dependence of multiple scattering reaches a plateau. In this regime and assuming the phase function to be constant around pi, we formally demonstrate Platt's modification of the single-scattering lidar equation, with a parameter eta(P) accounting for the reduction of the effective scattering coefficient defined so that (1 - eta(P)) is the amount of energy scattered in the forward peak. Then, to cope with nonconstant backscattering functions, we discuss the introduction of an effective backscattering coefficient that is an average of the scattering probabilities around pi.     

Lidar ratio and depolarization ratio for cirrus clouds

We report on studies of the lidar and the depolarization ratios for cirrus clouds. The optical depth and effective lidar ratio are derived from the transmission of clouds, which is determined by comparing the backscattering signals at the cloud base and cloud top. The lidar signals were fitted to a background atmospheric density profile outside the cloud region to warrant the linear response of the return signals with the scattering media. An average lidar ratio, 29 +/- 12 sr, has been found for all clouds measured in 1999 and 2000. The height and temperature dependences ofthe lidar ratio, the optical depth, and the depolarization ratio were investigated and compared with results of LITE and PROBE. Cirrus clouds detected near the tropopause are usually optically thin and mostly subvisual. Clouds with the largest optical depths were found near 12 km with a temperature of approximately -55 degrees C. The multiple-scattering effect is considered for clouds with high optical depths, and this effect lowers the lidar ratios compared with a single-scattering condition. Lidar ratios are in the 20-40 range for clouds at heights of 12.5-15 km and are smaller than approximately 30 in height above 15 km. Clouds are usually optically thin for temperatures below approximately -65 degrees C, and in this region the optical depth tends to decrease with height. The depolarization ratio is found to increase with a height at 11-15 km and smaller than 0.3 above 16 km. The variation in the depolarization ratio with the lidar ratio was also reported. The lidar and depolarization ratios were discussed in terms of the types of hexagonal ice crystals.     

Lidar extinction methods applied to observations of obscurant events

The SRI four-wavelength (0.53-, 1.06-, 3.8-, and 10.6-microm) lidar system was used during the Smoke Week VI/SNOW-TWO field experiments to observe range-resolved backscatter and target-reflected laser energy along a horizontal path intersected by test obscurant aerosols. Collected data are analyzed in terms of extinction coefficients and transmissions along laser propagation paths using three different lidar signature methods.     

Simulations of the observation of clouds and aerosols with the Experimental Lidar in Space Equipment system

We carried out a simulation study for the observation of clouds and aerosols with the Japanese Experimental Lidar in Space Equipment (ELISE), which is a two-wavelength backscatter lidar with three detection channels. The National Space Development Agency of Japan plans to launch the ELISE on the Mission Demonstrate Satellite 2 (MDS-2). In the simulations, the lidar return signals for the ELISE are calculated for an artificial, two-dimensional atmospheric model including different types of clouds and aerosols. The signal detection processes are simulated realistically by inclusion of various sources of noise. The lidar signals that are generated are then used as input for simulations of data analysis with inversion algorithms to investigate retrieval of the optical properties of clouds and aerosols. The results demonstrate that the ELISE can provide global data on the structures and optical properties of clouds and aerosols. We also conducted an analysis of the effects of cloud inhomogeneity on retrievals from averaged lidar profiles. We show that the effects are significant for space lidar observations of optically thick broken clouds.     

Light tunneling in clouds

Solar radiation, traveling outside cloud water droplets, excites sharp resonances and surface waves by tunneling into the droplets. This effect contributes substantially to the total absorption (typically, of the order of 20%) and yields the major contribution to backscattering, producing the meteorological glory. Usual computational practices in atmospheric science misrepresent resonance contributions and cannot be relied on in the assessment of possible anomalies in cloud absorption.     

Lidar profiles of fish schools

A lidar system was used in a seawater tank to measure the average diffuse reflectivity of live sardines. Diffuse reflectivity was measured to be 10 % for a copolarized laser return and 3 % for a cross-polarized return. We used these calibration measurements to infer the density of sardines in areas of the Southern California Bight from vertical profiles obtained with the lidar mounted on a ship. Within schools densities up to ~0.01 kg m-3 were observed. During hourly survey periods total habitat densities up to ~2 x10-3 kg m-2 were observed.     

茶叶中生物碱的分析方法概述

在查阅1907年以来国内外所有关于茶叶生物碱分析方法研究文献的基础上,结合茶叶中的生物碱及其分析方法现状,对茶叶中咖啡碱、可可碱、茶碱等生物碱的主要分析方法进行了系统地介绍,并对分光光度法、近红外光谱法、薄层色谱法、高效液相色谱法、毛细管电泳法和质谱法等主要分析方法的特点进行了评述,提出对茶叶中生物碱测定方法实行标准化,是实现茶叶生物碱准确定量分析和提高茶叶品质质量的重要途径与保证.     

Glory of clouds in the near infrared

Spectrally resolved visible and infrared images of marine stratus clouds were acquired from the NASA ER-2 high-altitude aircraft during the 1987 First International Cloud Climatology Program Regional Experiment. The images were obtained by cross-track scanning radiometers. Data images at nearinfrared wavelengths show frequent and readily apparent brightness features that are due to glory single scattering. The observations and subsequent analysis by radiative transfer calculations show that the glory is a significant feature of near-infrared solar reflectance from water clouds. Glory observations and calculations based on in-cloud microphysics measurements agree well. The most dramatic difference from the visible glory is that the scattering angles are significantly larger in the near infrared. The glory is also apparently more distinct in the near infrared than in the visible, as scattering size parameters are in a range that effectively produces a glory feature, and also there is less obscuration bymultipe-scattering reflectance because of absorption of radiation by droplets in the near infrared. For both the visible and the near infrared, the principal factors that wash out the glory are dispersion and, to a lesser degree, the effective radius of the cloud droplet-size distribution. The obscuration by multiple scattering in optically thick clouds is secondary. Rather than being a novelty, glory observations would be an accurate and unambiguous technique to sense the droplet size of water clouds remotely.     

Lidar frequency modulation vibrometry in the presence of speckle

We report laboratory target vibration measurements that use an easily aligned and adjusted fiber-based 1.5-microm heterodyne lidar. The targets are simple spherically curved retroreflectors with well-controlled vibration frequencies and amplitudes. A rotating ground-glass screen creates Gaussian speckle. We wish to understand the modulated and fast-fading lidar returns seen from real target. We frequency demodulated the recorded laboratory data by phase differencing to provide estimates of dphi/dt, where phi is the phase of the received carrier-plus-noise phasor. Experimental results for signal strength and signal-to-noise ratio, for specific target modulation parameters, agree well with our recently developed dphi/dt correlation-function theory.     

茶叶中色素的测试方法概述

在参阅1907年以来国内外关于茶叶色素分析的150余篇文献的基础上,对茶叶中色素的分析方法做了较系统的比较与研究,并针对茶叶色素的特点,就茶叶样品的前处理方法及目前常用的分析方法(主要包括Roberts法、柱层析法、高效液相色谱法和毛细管电泳法等)进行了评述,建议对茶叶色素测定的前处理,测定条件及最佳测试方法实行标准化,以确保测试结果的可比性、可靠性.     

一台监测高空钠层的激光雷达系统

介绍了一台监测高空钠层的激光雷达,通过共振荧光方法探测80-110km高度的钠层密度。雷达系统使用直径为1m的大口径接收望远镜,由Nd：YAG激光器泵浦染料激光器,波长589nm,脉冲激光能量77mJ。文中详细介绍了系统结构及光束自动调整、波长校正等系统特征技术,最后给出系统实测结果并分析。     

Approximations of polydispersed extinction

A method to evaluate the polydispersed extinction efficiency rapidly is presented. The method can be used for any shape for which a monodisperse code or expression is known and any polydispersion for which a second moment inverse can be computed. Integration can be performed over any interval of the distribution function. Additionally, and if required, arbitrary accuracy can be obtained. This approach is applied to spheres and randomly oriented spheroids with nth-order log-normal and modified gamma particle distributions.     

移动式机动车激光测速仪的校准

针对移动式红外机动车激光测速仪的测量原理,详细描述了一种基于时间延迟的校准方法.采用虚拟仪器技术的机动车激光测速仪校准系统,能够将激光测速仪发射的905nm测量脉冲激光光束进行特定时间量的延迟以模拟其在空气中对应的传播距离,完成机动车激光测速仪在(20～250)km/h时速范围内任意速度值的实验室准确校准,模拟速度不确定度优于0.5%(k=2).