In the recent years, the most country in the word attach importance to the environmental and the protection of
environmental doubly. The differential absorption lidar (DIAL)operating in the infrared wavelengths is a powerful
standoff sensor for rapid remote detection of chemical emissions. It represents also a powerful technique for
pollution monitoring of the atmosphere environment. Whereas, the numerical simulation system of DIAL has been
shown that is a powerful tool for system design and performance evaluation and improved performance of system,
along with research new information processing algorithm provided with the laboratory environment.
In this Paper, a DIAL operating in the infrared(LWIR)numerical simulated system is established. It can simulate
both traditional two-wavelength DIAL and multi-wavelength DIAL. It simulates the directional or scanning two
operational modes. One can obtain information by it such as gas kind, concentration and distribution and verify
the information processing algorithms visually. It can generate the return signals and can calculate their SNR
value for various simulated environment and weather and system conditions visually. In the paper, first review
laser light atmospheric propagation characteristic and then, the environmental models is ascertained including the
effects of the atmosphere attenuates and scatters, the atmospheric turbulence and the roughness target producing
reflective speckle and so on. Especially, the DIAL simulated system includes some new information processing
algorithms of discriminating target gases and estimating their concentration. By now, the DIAL simulated system
combined with this information processing algorithms has not been reported.
Rotorcraft flying in low-altitude is endangered by power lines or telephone wires. The development of automated tools that can detect obstacles in the flight path and warn the crew would significantly reduce the workload of pilot and increase the safety. Detection and warning are rudimental demand and desire for Helicopter Avoidance Obstacle System (HAOS). And that, An advanced HAOS may be capable of classifying thin obstacles and enhanced vision with distances of obstacles. A laser 3D imaging system for helicopter avoidance obstacle (HAO) had been developed successfully. The laser 3D imaging helicopter avoidance obstacle system can not only detect thin obstacles but also catch more information of all objects of the area in front of the helicopter as possible. Then the information is transformed into intuitionist 3D image modality. In this paper, special features and characteristic of the laser imaging system for HAO are analyzed and discussed. Several design gist for this system are proposed. Especially, the developed zero backlash imaging technology and real-time dynamic imaging synchronizing with radar space scanning are described. The technique implementation problem and the system structure are given as well. Finally, the results of system ground test are presented. The ground test of the developed laser imaging system has demonstrated that the developed imaging system performance can achieve and satisfy commendably the requirements of the mission to prevent "wire strike".
Differential absorption lidar (DIAL) has proved to be an important tool for remote sensing of trace gases in the atmosphere. As DIAL systems are affected by various noise factors such as atmospheric turbulence, target speckle, detection noise and so on, the measured concentration is corrupted by noise, and cannot be estimated accurately. However, when observations, predictions, estimations, and various covariance of Kalman filter algorithm are decomposed into lower resolution levels, due to filtering effects of wavelet transform, noise can be restrained while behavior of concentration is exposed. In this paper, a novel multiresolution Kalman filter algorithm is applied to estimate the path-integrated concentration (CL) from DIAL time series data where measurements are available at only one resolution level, and uses the stationary wavelet transform (SWT) as a means for mapping data between different resolution levels. The algorithm was evaluated for a variety of synthetic lidar data created with a program designed to model the various noise sources, including atmospheric turbulence, reflective speckle, and detection noise, which affect lidar signals. The simulation results show that our algorithm is effective in improving the measurement accuracy of gas concentration in DIAL and performs better than Kalman filtering and SWT visually and quantitatively.
This paper presents the new concept in the field of imaging radar system, the concept of digital receiver. The paper presents not only the digital receiver model, also every function is describe in detail. The necessity of digitizing for the laser imaging radar reception is discussed, and the feasibility of digital reception is demonstrated by research results and laboratorial data.
Diode laser imaging is one of the advanced sensors. It is best suited for the aerospace flight environment. We have developed a 40<SUP>K</SUP> X 8 bit pixels/sec diode laser imaging system, and this system was authenticated by specialists last year. This paper describes several important problems for intensity imaging which include improving laser power utilization ratio and receiving sensitivity in a laser imaging system. Improvement SNR of an imaging system is a criterion of analysis and comparison. Waveform design of both the maximum power limited and average power invariant are analyzed separately. In order to understand avalanche gain contribution to receiver SNR, performance comparison of receiving is evaluated for detection type and operation state. The comparison includes intensity modulated (IM)/coherent detection (CD) and IM/Direct detection (DD) for different avalanche gain values and different photodetector load resistance values. According to the relations between receivable return power and SNR, a series of curves are calculated by computer. These curves clearly show the best detecting type for various receiver power levels. These results of analyses provide the theoretical basis of transmitter and high sensitivity receiver design. These analyses also show that in intensity imaging system correct waveform selection can make 4 dB improvement on SNR and reasonable receive trade-off design can make about 30 dB improvement on SNR.