In many opto-electronic system, the requirements to the ability of optical filtering and optical frequency discrimination become higher and higher. If the traditional optical techniques are used, the problems of system stability, technical complications and costs of the system will be encountered. However, by using the high optical resolution technique based on atomic transitions, most of problems mentioned above can be overcome. When the atomic transition technique is used in the optical receiver, the same technique must be used in optical transmitter to control the laser frequency. In this way, an atomic transition controlled optical channel is formed. Here the function, principle and structure of an atomic controlled channel and some opto-electronic system using atomic channel technology are presented.

Na lidar, meteor radar and medium frequency (MF) radar are three significant techniques in measuring mesospheric horizontal wind fields and were extensively used nowadays. With the three instruments, simultaneous observations were operated for many nights in Hawaii from 2002 to 2005. The horizontal winds observations as long as 8 hours at two nights of July 9, 2002 and October 23, 2003 were chosen and analyzed to study the differences of the three techniques. It is found that the wind amplitudes observed by Na lidar and meteor radar are agreeable with each other normally, but both much larger than MF radar observations. The vertical variations of the nightly mean wind observations show that the three instruments could obtain consistent (evidently discrepant) wind observations when the wind amplitudes and the corresponding shear are weak (strong).

The middle and upper atmosphere temperature and wind fields are important parameters to study atmospheric dynamics. A sodium temperature/wind lidar system of University of Science and Technology of China (USTC), which can be used for the temperature and wind measurement with high resolution in the mesopause region (80~105 km) is presented briefly. Theory for measuring atmospheric temperature and wind of the lidar is discussed. The transmitter, receiver, photoelectric detecting subsystem, acquisition subsystem and timing control subsystem are described respectively. Finally, the temperature and wind results are given, while the temperature profile observed by sodium lidar is compared with SABER observed, the wind observed by sodium lidar is compared with ground-based meteor radar observed in Wuhan.

The first daytime sodium lidar observations in China were made in Wuhan (30°30′N, 114°E). In a long observation cycle lasting more than two days, the sodium layer presented strong diurnal variations. The sodium column density, layer width and centroid height, all presented 24 h periodic variations. The density variation at each height also presents a clear 24 h downward wave phase propagation. All these can be attributed to a prominent diurnal tidal wave perturbation, and the derived phase agrees very well with that obtained from the GSWM00 model. A large sodium diurnal variation was also presented in three other shorter daytime observations, while the mean diurnal variations of the sodium layer present a prominent structure of diurnal tidal wave propagation. These results agree with early reports, namely, that the diurnal tide component is the dominant tide wave over Wuhan.

Aerosol production and transmission over oceans are related to wind in some extent. Research on the relationship between wind speed and aerosol might increase the accuracy of forecast, which has important meaning to atmospheric model. The relationship between aerosol optical depth (AOD) and sea surface wind speed was explored using remotely sensed data from cloud-aerosol lidar with orthogonal polarization (CALIOP) on board CALIPSO satellite and collocated advanced microwave scanning radiometer (AMSR-E) on board AQUA satellite. Measurements in eight months (January, April, July and October, 2007 and 2008) were used to study the relationship between sea surface wind speed and AOD at the wavelength of 532 nm, and its changes with seasons and years. The results show that, in cloud free condition, aerosol optical depth over global ocean is related to sea surface wind speed. For wind speed less than 12 m/s, AOD increases with wind speed. For wind speed between 4 m/s and 12 m/s, AOD increases quasi-linearly with the increase in surface wind. For higher wind speed values, i.e. wind speed is more than 14 m/s, and the relationship shows a tendency toward leveling off.

For retrieving sea surface wind speed, good results were achived with CALIPSO lidar night data. During daytime, spaceborne lidar has a poor signal to noise ratio due to the irradiation of direct sunlight and the sky. Based on the existing retrieval model, sea surface wind speeds of day and night were retrieved using CALIPSO lidar 532 nm day and night single-shot data of January, April, July and October in 2007, with aerosol optical depth (AOD) for two-way atmospheric transmittance correction. The collocated version 7 AMSR-E sea surface wind speeds were used as the true values for comparison. The results show that, it is feasible to use CALIPSO daytime lidar data for sea surface wind speed retrieval, and the precision can be increased with the use of appropriate retrieval model.

The cloud vertical structure (CVS) acts an important aspect of cloud characteristics and atmospheric model. The vertical distribution statistics of clouds over China Sea and adjacent sea area were derived from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) level 2 version 3 lidar cloud layer data from 2007 to 2010. The results show that the cloud occurrence frequencies (COF) of single and multi-layer clouds over the mentioned area are different, and the layer-top-altitude (LTA) occurrence frequencies have obvious difference with latitude. High clouds (10~20 km) have high occurrence frequency near equator. Because there are some opacity clouds, the result of layer-number and LTA may be smaller than the real situation.

A Doppler lidar was reported in which the laser frequency is stabilized and the backscattered light frequency is discriminated by a multi-peak and less-peak atomic Faraday anomalous dispersion optical filter (FADOF), respectively. The transmission spectrum of FADOF is stable as it is based on an atomic transition, and slightly tunable with a magnet due to Zeeman effect. The high frequency stability of FADOF provides a high velocity accuracy, and the tunability of FADOF transmission spectrum makes the measurement range flexible. An experimental lidar system was described based on cesium FADOFs, and the experimental error is of 0.74 m/s over velocities ranging from -40 to 40 m/s.

Doppler lidar observation carried out in the southern suburbs of Beijing from March 21, to April 19, 2011, was presented focusing on analysis of the aerosol extinction coefficient retrieved by the Fernald method. Combined with data obtained by the radiosonde at the same period, it illustrates the characteristics and changes of aerosols in the boundary layer and lower stratosphere. Observational data indicates that in the cloudless and clear day, aerosol extinction coefficient descends gradually from low to high altitude. In cloudy weather, aerosol extinction coefficient increases at the cloud layer. In addition, the low-altitude aerosol extinction coefficient has apparent diurnal variation characteristics that aerosol extinction coefficient in the morning is lower than that of evening. During the experiment, the mean optical thickness from the ground to 10 km is 0.52.

Doppler wind lidar is able to measure atmospheric wind field with high spatial and temporal resolution. A mobile Doppler wind lidar for wind profile and three-dimension wind field measurements was developed by Ocean University of China and then operated by China Meteorological Administration. In order to verify the measurement performance of the lidar, a synchronous observation campaign with the mobile lidar and radiosonde was carried out in the Spring of 2011 and obtained 55 intercomparison measurements. It introduces the synchronous observation campaign, shows a case study of wind profile intercomparison by lidar and radiosonde, and statistically analyzes all the intercomparison measurements. The results of the synchronous intercomparison show that the root mean square deviation of wind speed measured by lidar and radiosonde is 2.76 m/s. By means of analyzing the deviation, the wind profiles measured by lidar are proved to be accurate.

Based on Fernald’s and Klett’s method, a new expression of the atmospheric extinction coefficient boundary value was presented. This expression was a formula that has two more terms than Collis’ method. The absolute value of the two terms may account for 78.2% of the term in Collis’ method and have opposite sign. Taking the two terms into consideration, aerosol optical depth (AOD) derived by lidar is closer to the observed one by sun-photometer. With the change of reference height, the derived AOD ranging from 0.20 to 0.25 and the variance is about 0.003, showing that this approach is independent from reference height and relatively stable. 424 clear sky data were selected in the inversion. AOD derived by lidar is 7.4% bigger than the observed one. The correlation coefficient is 0.932, the relative error is 10.9%, the absolute error is 0.03 and the variance is 0.02. The approach has a better performance when AOD is less than 0.45.

In order to understand the spatial and temporal variations of cirrus over semi-arid areas in Northwest of China, macrophysical and optical characteristics of cirrus clouds were observed by micro pulse lidar (MPL-4B) over Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL, 35
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N, 104
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E). The structures and optical properties of the cirrus clouds as well as their spatial and temporal variations were discussed and analyzed. The results show that cirrus clouds change from thin to thick, observed ranging from 7 to 10 km, with a mean thickness of (2.0±0.5) km. During this period, the samples have temperature between -51℃ and -39℃. The cloud optical depth increases and then decreases with increasing geometrical depth, ranging from 0.084 to 1.649, with a mean value of 0.651±0.403. Lidar ratio of cirrus clouds is (17±17) sr and it’s found that lidar ratio of optically thin cirrus is larger than that of thick cirrus. Thin cirrus clouds with ambient temperature below -45℃ occurr above 8.6 km and its thickness is lower than 1.8 km. The lidar ratio of thin cirrus is between 5 and 69 sr.

To compare the consistency of cloud base heights measured by some instruments, the Meteorological Observation Center of China Meteorological Administration firstly organized a nearly 5-month campaign employing four ceilometers, two infrared cloud measuring systems, one Total-Sky-Imager and one cloud radar. The campaign was carried at the observation field within the campus of Nanjing University of Information Sciences & Technology. Preliminary analysis of 3-month cloud base heights obtained from most of the above instruments shows that the data among 3 ceilometers are comparatively consistent, the consistency between the two infrared cloud measuring systems is slightly worse than that from ceilometers, the consistency of observed cloud base height of the first cloud layer between cloud radar and ceilometers is comparatively low, but is much better than that between cloud radar and infrared cloud measuring system.

A Raman lidar was developed for atmospheric CO2 measurements in the low troposphere in Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. Combined with real atmospheric condition, atmospheric CO2 uncertainty was analyzed using the Raman lidar measurement cases and observation results by CO2 analyzer. Analyzed results show that the lidar reveals fine stability and higher accuracy. For example, it’s uncertainty can be limited within 1.2 ppm up to 1km altitude and 2.5 ppm up to 2 km altitude under good weather condition.

For monitoring the atmospheric aerosol, a micropulse lidar (MPL) system was developed by Shandong Academy of Sciences Institute of Oceanographic Instrumentation (SDIOI) to investigate structural and optical properties of clouds and aerosol. The structure and main technical parameters of the MPL are introduced. The transmitter is based on a diode-pumped Nd:YAG laser which delivers up to 6 μJ pulse energy at a pulse repetition rate of 2.5 kHz. The receiver utilizes a commercial 20 cm diameter Schmidt-Cassegrain telescope, a 0.5 nm narrowband interference filter, and a photon counting PMT detector. The system observed tropospheric atmospheric aerosol of Qingdao and the results show that the system can measure the tropospheric aerosol continuously and well reflect the space and time distribution of aerosol.

Following the trend in the world, a 512 channels ICCD was used as ocean lidar’s detector. With a 70 μJ single pulse energy, 355 nm laser and the 512 channels ICCD, the performance of airborne ocean lidar was simulated in laboratory. The water sample was put in 5 m and the fluorescence signal was collected with a 100 mm diameter lens. The experimental result shows a good signal noise ratio. Based on the simulation experimental results, it can be included that a real airborne ocean lidar with a 20 Hz, 80 mJ single pulse energy, and 200 mm diameter collection telescope has nearly the same performance with the lab lidar system.

The lidar geometric factor describes the overlap between the laser beam and the receiver of field of view in differential absorption lidar. It is an important system parameter in differential absorption lidar. An experimental determination method of the lidar geometric factor is presented based on the comparison of aerosol scattering ratio profile derived from the signals measured by differential absorption lidar and Mie lidar simultaneously. The approach provides a means to determine the lidar geometric factor without an explicit knowledge of all lidar system parameter, such as the telescope diameter, laser beam divergence, telescope of field of view et al. The application of the proposed method can reduce the ozone measurement error of differential absorption liar and improve the potential of differential absorption lidar to investigate the spatial and temporal distribution characteristics of ozone.

Doppler lidar was widely used for wind measurement. Compared with Fabry-Perot(F-P) interferometer and Fizeau interferometer, Mach-Zehnder(M-Z) interferometer have the advantages of high transmittance, wide spectral range, wide field of view and producing linear fringe. It can realize wide wind range detection and make up smaller detection range and nonlinear detection sensitivity of present technology. Wind measurement theory based on fringe imaging M-Z interferometer is analyzed. The parameters of interferometer system are optimized and then the system is designed by using a numerical simulation. The results show that the wind velocity retrieved agrees with theoretical wind velocity.

An all-fiber Raman water vapor lidar system was proposed and designed based on fiber Fabry-Perot (F-P) filters in the visible wavelength domain, to achieve the fine-detection of the atmospheric water vapor and aerosol properties. The influences of cavity loss and the reflectance on the fitness, the transmission peak and bandwidth of fiber F-P filters were analyzed. Results show that the fiber F-P filter features a higher transmission peak and narrower bandwidth under the condition of the F-P cavity loss less than 3%. The combination of fiber band-pass filters and the two-cascade fiber F-P filters was used as fiber spectroscopic system and the corresponding parameters were designed to achieve narrow-band high-peak transmission of the Raman signals of water vapor (660 nm) and nitrogen (606 nm) and Mie-Rayleigh signals (532 nm), respectively, and obtain high rejection-rate of stray lights. By numerical simulations of the intensity distribution of returned signals, the water vapor vertical profile and the detection signal to noise ratio(SNR) were obtained respectively, to verify the feasibility of the system.

An all-fiber rotational Raman lidar spectroscope constructed by fiber Bragg grating and fiber coupler in visible region was designed. The fiber Bragg grating with 530 nm central wavelength was successfully fabricated through phase mask directly inscribing, and then its transmissivity and reflectivity were experimentally tested. The high tuning sensitivity cantilever system was designed to enhance the matching performance between the central wavelength of fiber Bragg grating and the rotational Raman spectral line of atmosphere molecules. The experimental results show that the fiber Bragg grating in visible region possesses 95% reflectivity and 0.3 nm full width at half maximum, and that the strain tuning system may possess sensitivity of 18 pm/r within the ±0.6 nm range.

The data acquisition and visualization software of Mie lidar was developed based on LabVIEW. It can acquire and display data of lidar in real time by LabVIEW calling the dynamic link library of photon counting card (MSA300). The extinction coefficient was inversed by Fernald method and displayed with time-height-indication (THI) figure. The software converts and saves the data as ASCII format to be post-processed and analyzed. Lidar experiments show that the atmospheric data, extinction coefficients and THI can be displayed in real time by the software to intuitively understand the spatial and temporal changes of the aerosol and cloud.

A micro-pulsed Mie scattering lidar system operated in analog detection mode was designed and built for routine observations of aerosol optical properties and cloud in the lower troposphere, particularly in the high intense aerosol gathered atmospheric area. The configuration of lidar and its design methods including the hardware and automatic control and data acquisition software were described in details. The experimental results in Xi’an area illustrate that the system can measure the atmospheric aerosols up to the range of near 3~5 km at daytime and 15 km at nighttime under the measurement conditions of laser energy of 50 μJ with repitition rate 1 kHz, signal averaging time of 40 s, a receiving aperture 254 mm, range resolution of 7.5 m and analog detection model. It can provide scientific measurement data for understanding the atmospheric environment change, particularly the particulate pollutant generation, transmission and diffusion characteristics.