Using the monthly data sets during 1951-2008 from standard upper-air stations, the spatial and seasonal distributions of upper turbulence over China are studied, and the atmospheric turbulence intensity at the pressure levels of 200hPa, 100hPa and 50hPa are given in this paper, providing scientific reference for relevant experiments. The intensity of atmospheric turbulence is closely related to height; at 200hPa pressure level, a downward trend of turbulence intensity from north to south is shown over China; at 100hPa, the turbulence is decreasing from south to north, weak turbulence occurs in the area north to 40°N; at 50hPa in near space, the turbulence in the west is slightly weaker than that in middle and east of the country. Influenced by seasonal variations of the mean circulations at each altitude, strong turbulence always occurs in winter while weak one in summer; but at 100hPa, the distribution of turbulence is evenly all over the country in summer, while weak turbulence occurs above the Tibetan Plateau and north of 40°N in winter; at 50hPa, the turbulence is weak in autumn, and a bit strong in summer. On the whole, the results could reflect the characteristic distributions of atmospheric optical turbulence in most general circumstances, and the most important value is to give the relative regional distributions of turbulence, to evaluate regional optical conditions on a macro scale.
Remote sensing of ranged-resolved profiles of atmospheric turbulence is necessary and important for many applications in
astronomical and adaptive optics communities. In order to obtain turbulence profiles in atmospheric boundary layer, a
device is developed and experiments has been carried out. In the experiments, laser guide stars are formed at several
successive altitudes by projecting pulsed laser, returned signals are received by two receiving telescopes and the images of
the returned signals are formed by a imaging device. Variance of centroids′ distance is derived from the images with two
spots at the same altitude and ranged-resolved profile of the variance is obtained. So, based on a inversion algorithm,
atmospheric turbulence profiles are retrieved from differential image motion variance of distance of centroids at various
altitudes. The structure constants of refractive index of atmosphere range from 10-14m-2/3 at lower altitudes to 10-16m-2/3 at
higher altitudes are remote sensed experimentally. The results show it is a effective method that combined laser guide stars
with differential image motion method and could sense atmospheric turbulence profiles remotely in real time.
Atmospheric turbulence increases bit error rate and degrades beams quality for wireless laser communication links as
laser light propagation in the turbulent atmosphere, and atmospheric refractive index structure constant is an important
parameter for statistics of atmospheric turbulence. Characteristics of atmospheric turbulence in the atmosphere varies
randomly and the experiments in the real atmosphere are expensive, so it is an important way to simulate atmospheric
turbulence in laboratory for investigation on laser beams propagation in through the atmosphere. The structure parameter
of the atmospheric turbulence in laboratory was measured based on measurement of angle-of-arrival (AOA) fluctuations
of centroids as laser beam through the simulated-turbulence. The results shows a good agreement with the previous result
measured by thermal method, the strength of simulated-turbulence was 1000 times stronger than that in the real
atmosphere. The characteristics of turbulence varies temporally with air temperature and wind velocity, and statistics of
atmospheric turbulence was presented for various air temperature and wind velocity along the propagation path.
Optical scintillation degrades beam quality as laser beams propagation in the atmosphere and increases rates of code-error
for high-data-rate laser communication in the atmosphere. The scintillated irradiance depends on integrals of atmospheric
turbulence strength along the propagation path. For the shorter path-length and weaker atmospheric turbulence, the
integral is smaller, and the Rytov weak fluctuation theory can solve the problem successfully. However, for longer
path-length and/or stronger atmospheric turbulence strength, multiple scattering events must occur and result in saturation
of irradiance scintillation. The irradiance scintillation of laser beams propagation in the near ground turbulent atmosphere
is investigated for the case of plane wave and spherical wave at various typical atmospheric turbulence strengths and inner
scale of atmospheric turbulence. The dependence of irradiance scintillation on turbulence strength, path-length, and inner
scale is presented for the plane wave case and spherical wave case. The results on plane wave case and spherical wave case
are compared.
Optical turbulence effects, such as irradiance scintillation, fluctuation of arrival angle, beam wander, and beam
spreading, etc., degrade the beam quality as a laser beam propagates in the turbulent atmosphere. Of these effects, the
scintillation is a dominant effect in many applied fields such as high-data-rate laser atmospheric communication,
astronomical adaptive optics imaging, and other laser engineering. The scintillated irradiance depends on integral of
optical turbulence along the propagation path and it induces a perturbation on the amplitude of the electro-magnetic
field. As the integral is smaller, the Rytov weak fluctuation theory can solve the problem successfully. However, with an
increase in the strength of the atmosphere turbulence or the path length, multiple scattering events must occur and result
in saturation. The irradiance scintillation of laser beam propagation in a slant-path in the boundary-layer is investigated
for the cases of weaker to moderate-to-stronger turbulence, various path-length and elevation angles. The dependence of
scintillation on turbulence strength, path-length, and elevation angle is presented and the results are compared with the
Rytov theory.
A new heuristic optical scintillation model developed recently is viewed and it is a available method in investigation on laser beams propagation in turbulent atmosphere. The irradiance scintillation is treated as a modulation of small scale scintillation by large scale scintillation as laser beams propagation in turbulent atmosphere, the irradiance scintillation is investigated for uplink propagation at various receiving heights and zenith angles for different atmospheric turbulence model. The influences of receiving height and zenith angle on the irradiance scintillation is analyzed for different atmospheric turbulence model, and the conclusions deduced are useful for farther future researches.
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