Streak images obtained by the streak tube imaging lidar (STIL) contain the distance-azimuth-intensity information of a scanned target, and a 3-D reconstruction of the target can be carried out through extracting the characteristic data of multiple streak images. Significant errors will be caused in the reconstruction result by the peak detection method due to noise and other factors. So as to get a more precise 3-D reconstruction, a peak detection method based on Gaussian fitting of trust region is proposed in this work. Gaussian modeling is performed on the returned wave of single time channel of each frame, then the modeling result which can effectively reduce the noise interference and possesses a unique peak could be taken as the new returned waveform, lastly extracting its feature data through peak detection. The experimental data of aerial target is for verifying this method. This work shows that the peak detection method based on Gaussian fitting reduces the extraction error of the feature data to less than 10%; utilizing this method to extract the feature data and reconstruct the target make it possible to realize the spatial resolution with a minimum 30 cm in the depth direction, and improve the 3-D imaging accuracy of the STIL concurrently.
Laser Rayleigh-Brillouin scattering is an effective non-intrusive method for measurement of density, temperature and pressure in gas flows. In theory, the power of Rayleigh-Brillouin scattered laser light is proportional to the gas density, the full width at half maximum (FWHM) and the Brillouin shift of the Rayleigh-Brillouin scattering spectrum is related to the gas temperature and pressure, respectively. In this paper, a measurement device based on Fabry-Perot interferometer (FPI) is designed to measure the Rayleigh-Brillouin spectrum of nitrogen gas. The experimental data is obtained at different pressures under room temperature conditions. The L3 model is used to fit the experimental data to obtain the FWHMs and Brillouin shifts of the Rayleigh-Brillouin profiles. The composite Rayleigh-Brillouin profiles which consist of Rayleigh peak, stokes peak and anti-stokes peak are represented by three distinct peaks of Lorentz functions. Fitting results show that the error of FWHMs and Brillouin shifts obtained by L3 model is less than 10% compare with the Tenti S6 model. Some factors that affect the measurement accuracy of the Rayleigh-Brillouin parameters are also analyzed and discussed.
Laser Rayleigh-Brillouin scattering is a powerful diagnostic tool for the study of gas flow properties. It provides an effective method for non-intrusive measurement of density, temperature and velocity in the gas flow. The received scattered laser light power is proportional to the gas density, the linewidth of the Rayleigh-Brillouin scattering spectrum is related to the gas temperature, and the Doppler frequency shift of the peak of the Rayleigh-Brillouin scattering spectrum is related to the gas velocity. The Rayleigh-Brillouin scattering spectrum can be measured by a Fabry-Perot interferometer operated in the imaging mode where an intensified CCD camera is frequently used to record the interference patterns of the Fabry-Perot interferometer. The Rayleigh-Brillouin scattering spectrum is then reconstructed from the measured data deconvolved with the Fabry-Perot instrument function. In this paper, the analysis and design of an imaging Fabry-Perot interferometer for the measurement of the Rayleigh-Brillouin scattering spectrum in the gas flow is presented. Some factors that limit the performance of the imaging Fabry-Perot interferometer are analyzed and discussed.
There is currently considerable interest in developing electro-optic systems for underwater imaging classification and
identification of submerged objects such as fish shoals and mines. The imaging systems can be divided into active
imaging systems and passive imaging systems. The main feature of the passive imaging systems is that they haven't
illumination sources and depend on lights from targets or surroundings. The active imaging systems use light sources to
illuminate the targets and collect the reflection from the targets. The advantages of active imaging systems over passive
imaging systems are high contrast and without the affection of environment sources. The gated Intensified CCD (ICCD)
cameras are widely used in the active imaging systems because that the laser range-gated (LRG) technology is an
effective way to eliminate the backscattering noise. This paper is devoted to present a model for simulation and
evaluation the performance of gated ICCD cameras for airborne underwater applications. Some simulation results are
presented and discussed.
High-power lasers are widely used in various scientific, industrial and military applications. There is currently a desire
for precision measurement the beam quality of high-power lasers in order to evaluate the performance of the laser
systems and the operational effectiveness of chemical and solid-state high-power laser weapons. There are many
methods of beam quality determination, such as beam parameter product, encircled energy ratio BQ, Strehi ratio,
diffraction limit factor β and beam propagation factor M<sup>2</sup>. In this paper, a beam quality measurement device is developed
for high-power lasers. This device consists of a beam attenuator with large reflective ratio and minimal wavefront
distortion, an off-axis parabolic mirror, an imaging lens and an infrared focal plane array detector. The laser beam
intensity distribution, beam width, beam divergence and beam pointing stability can be obtained in real-time and the
beam quality can be evaluated by the various determinations through imaging process. Advantages and disadvantages of
these beam quality determination for evaluation the performance of the high-power lasers are analyzed and discussed.
The measurement uncertainties of relative parameters are also analyzed and discussed.
In ocean there are two kinds of bubbles according to mechanism of bubble generation. One case is bubble existing on the ocean surface and in the upper ocean due to breaking wave phenomena. The radius of bubbles changes from 10 micrometer to 1000 micrometer. Another one is for warship the bubbles varying size from 10 micrometer to 100 micrometer<sup>[1,2]</sup>. For later mechanism of bubble generation is due to change of a propeller's tip vortex flow field and interaction between cavitation and explosion bubbles. Assuming that the shape of bubble is spherical, Mie scattering model is used to analyze and calculate the behaviors of forward scattering and backscattering of bubble, such as the change of the normalized scattering amplitude intensity with bubble diameter, scattering angle, polarization direction, and laser wavelength. However, with increasing of the size of bubble and particularly while the bubble size is much bigger than that of incident laser wavelength we find the backscattering of bubbles approaches to zero using Mie scattering theory. Apparently, this is no agreement to experimental results. In this paper, the corresponding geometry optics scattering model including the size and shape of bubble is given, the forward scattering and backscattering are analyzed and calculated using the model. Finally, it can be seen that for geometry model there is good agreement to Mie scattering model while the size of bubble approaches to laser wavelength.