Finite aperture optical scintillometer for profiling wind and C(2)(n)

Using turbulence scintillation to assist object ranging from a single camera viewpoint

Image distortions caused by atmospheric turbulence are often treated as unwanted noise or errors in many image processing studies. Our study, however, shows that in certain scenarios the turbulence distortion can be very helpful in enhancing image processing results. This paper describes a novel approach that uses the scintillation traits recorded on a video clip to perform object ranging with reasonable accuracy from a single camera viewpoint. Conventionally, a single camera would be confused by the perspective viewing problem, where a large object far away looks the same as a small object close by. When the atmospheric turbulence phenomenon is considered, the edge or texture pixels of an object tend to scintillate and vary more with increased distance. This turbulence induced signature can be quantitatively analyzed to achieve object ranging with reasonable accuracy. Despite the inevitable fact that turbulence will cause random blurring and deformation of imaging results, it also offers convenient solutions to some remote sensing and machine vision problems, which would otherwise be difficult.

Humidity's influence on visible region refractive index structure parameter C(n)(2)

In the near-infrared and visible bandpasses optical propagation theory conventionally assumes that humidity does not contribute to the effects of atmospheric turbulence on optical beams. While this assumption may be reasonable for dry locations, we demonstrate that there is an unequivocal effect owing to the presence of humidity upon the strength of turbulence parameter, C(n)(2), from data collected in the Chesapeake Bay area over 100 m length horizontal propagation paths. We describe and apply a novel technique, Hilbert phase analysis, to the relative humidity, temperature, and C(n)(2) data to show the contribution of the relevant climate variable to C(n)(2) as a function of time.

Effects of saturation on the optical scintillometer

Measurements of the level of turbulence C(2)(n) have been successfully performed with the optical scintillometer. The success of this instrument is based on the observed fact that the variance of aperture averaged scintillation is described by weak scattering theory even for conditions in which strong scintillation is observed for point detectors. However, for sufficiently long propagation paths, the aperture averaged variance is affected by strong scattering. The effects of strong scattering are calculated theoretically and compared to experimental results. The physics of this regime are discussed and the important parameters investigated. The new range of validity of the optical scintillometer is discussed.

Estimation of the parameters of the atmospheric turbulence spectrum using measurements of the spatial intensity covariance

Estimates of the level of turbulence C(2)(n) and the inner scale of turbulence lambda(0) are obtained from measurements of the spatial covariance of laser scintillation in weak scattering conditions. Boundary layer turbulence is widesense nonstationary over time scales of <1 min but becomes locally wide-sense stationary on time scales of 2 min. The interpretation of the measurements is very sensitive to the form of the turbulence spectrum in the dissipation region.

Atmospheric stability from scintillation measurements

The Obukhov length L is an important meteorological parameter that quantifies the stability of the atmospheric surface layer. Consequently, routine monitoring of L with simple instruments is desirable. I describe here such a monitoring scheme, the SFS method, that has the added advantage of yielding a spatially averaged estimate of L. The SFS method-stability from scintillation-is based on measurements of the refractive-index structure parameter C(2)(n) with two matched scintillometers positioned at heights z(1) and z(2). A sensitivity analysis shows that the method can yield an estimate of the stability parameter xi = (z(1)z(2))((1/2))/L with factor of 2 accuracy in the ranges of -3 </= zeta </= -0.015 and 0.02 </=zeta </= 10, the stabilities most commonly encountered in the surface layer.