Wind measurements by the temporal cross-correlation of the optical scintillations

Development of a tunable diode laser absorption sensor for online monitoring of industrial gas total emissions based on optical scintillation cross-correlation technique

We report the first application of gas total emission using a DFB diode laser for gas concentration measurements combined with two LEDs for gas velocity measurements. In situ gas total emissions and particle density measurements in an industrial pipeline using simultaneous tunable diode laser absorption spectroscopy (TDLAS) and optical scintillation cross-correlation technique (OSCC) are presented. Velocity mean values obtained are 7.59 m/s (OSCC, standard deviation is 1.37 m/s) and 8.20 m/s (Pitot tube, standard deviation is 1.47 m/s) in a steel plant pipeline for comparison. Our experiments demonstrate that the combined system of TDLAS and OSCC provides a new versatile tool for accurate measurements of total gas emissions.

Determination of flow orientation of an optically active turbulent field by means of a single beam

The cross-flow orientation of an optically active turbulent field was determined by Fourier transforming the wander of a laser beam propagating in the ocean. A simple physical model for the measured effect is offered, and numerical simulations are performed. The simulations are in good agreement with measurements, validating the assumptions made in the model.

Optical anemometry based on the temporal cross-correlation of angle-of-arrival fluctuations obtained from spatially separated light sources

The temporal cross-correlation function of the angle-of-arrival (AOA) fluctuations of two optical waves propagating through atmospheric turbulence carries information regarding the average wind velocity transverse to the propagation path. We present and discuss two estimators for the retrieval of the path-averaged beam-transverse horizontal wind velocity, v(t). Both methods retrieve v(t) from the temporal cross-correlation function of AOA fluctuations obtained from two closely spaced light-emitting diodes (LEDs). The first method relies on the time delay of the peak (TDP) of the cross-correlation function, and the second method exploits its slope at zero lag (SZL). Over a 9 h period during which v(t) varied between -1.3 ms(-1) and 2.0 ms(-1), the maximum rms difference between optically retrieved and in situ measured 10 s estimates of v(t) was found to be 0.18 ms(-1) for the TDP estimator and 0.23 ms(-1) for the SZL estimator. Applicability and limitations of these two optical wind retrieval techniques are discussed.

Crosswind sensing from optical-turbulence-induced fluctuations measured by a video camera

We present a novel method for remote sensing of crosswind using a passive imaging device, such as a video recorder. The method is based on spatial and temporal correlations of the intensity fluctuations of a naturally illuminated scene induced by atmospheric turbulence. Adaptable spatial filtering, taking into account variations of the dominant spatial scales of the turbulence (due to changes in meteorological conditions, such as turbulence strength, or imaging device performance, such as frame rate or spatial resolution), is incorporated into this method. Experimental comparison with independent wind measurement using anemometers shows good agreement.

Wind profiling based on the optical beam intensity statistics in a turbulent atmosphere

Reconstruction of the wind profile from the statistics of intensity fluctuations of an optical beam propagating in a turbulent atmosphere is considered. The equations for the spatiotemporal correlation function and the spectrum of weak intensity fluctuations of a Gaussian beam are obtained. The algorithms of wind profile retrieval from the spatiotemporal intensity spectrum are described and the results of end-to-end computer experiments on wind profiling based on the developed algorithms are presented. It is shown that the developed algorithms allow retrieval of the wind profile from the turbulent optical beam intensity fluctuations with acceptable accuracy in many practically feasible laser measurements set up in the atmosphere.

Remote sensing of atmospheric winds using speckleturbulence interaction, a CO(2) laser, and optical heterodyne detection

Speckle-turbulence interaction can be utilized to measure the vector wind in a plane perpendicular to the line of sight from a laser transmitter to a target. A continuous wave source of around 1 W and operating at 10.6 microm, in conjunction with an optical heterodyne receiver, has been used to measure atmospheric winds along horizontal paths. A theoretical basis, the experimental apparatus, processing techniques, and experimental results are presented. The technique has been demonstrated for remote sensing of atmospheric winds along horizontal paths but also has potential for global remote sensing of atmospheric winds and for onboard wind shear detection systems for aircraft. The results show that rms accuracies of the order of 0.5 m/s are possible with averaging times as short as 2 s.