Wavelet-Based Optical Flow for Two-Component Wind Field Estimation from Single Aerosol Lidar Data

Abstract

A motion estimation algorithm was applied to image sequences produced by a horizontally scanning elastic backscatter lidar. The algorithm, a wavelet-based optical flow estimator named Typhoon, produces dense two-component vector flow fields that correspond to the apparent motion of microscale aerosol features. To validate the efficacy of this approach for the remote measurement of wind fields in the lower atmosphere, an experiment was conducted in Chico, California, in 2013 and 2014. The flow fields, estimated every 17 s, were compared with measurements from an independent Doppler lidar. Time series of wind speed and direction, statistical assessment of the 10-min averages, and examples of wind fields are presented. The comparison of 10-min averages at 100 m AGL reveals excellent correlations between estimates from the Typhoon algorithm and measurements from the Doppler lidar. Power spectra and spectral transfer functions are computed to estimate the filtering effects of the algorithm in the spatial domain.

Organic, Gas, and Element Geochemistry of Hydrothermal Fluids of the Newly Discovered Extensive Hydrothermal Area in the Wallis and Futuna Region (SW Pacific)

“…Video recordings could be used to estimate fluid velocities of the Carla and Obel X chimneys and of a few smokers at Kulo Lasi using for instance the Typhoon algorithm [123] ( Figures S8-S11). This optical flow method recovers the (2D) fluid flow from the apparent displacements, in an image sequence, of tracers advected by the flow.…”

Wind Energy Instrumentation Atlas

“…A Raman lidar detects atmospheric components (such as water vapor) by measuring the wavelength-shifted return from selected molecules (Strauch et al 1971). A Raman-shifted eye-safe lidar uses very short pulses of invisible, eye-safe, near-infrared electromagnetic radiation to sense aerosol particles and their variations and movement to quantify atmospheric motions (Mayor and Spuler 2004;Dérian et al 2015). Commercial lidars have a TRL >8.…”

Comparison of an analog direct detection and a micropulse aerosol lidar at 1.5 - μ m wavelength for wind field observations—with first results over the ocean

“…14 The REAL has resulted in impressive aerosol imagery that can be used with motion estimation algorithms to deduce vector wind fields. [18][19][20] The REAL transmitter, however, is large and challenging to maintain. It places very significant limitations on the embodiment of the entire instrument, sets substantial requirements for operation, and therefore reduces deployment opportunities.…”

“…This is achieved using a quantity that we call "image-SNR" (iSNR). 20 iSNR is defined as the ratio of the local standard deviation of spatially coherent relative backscatter signal σ I ðr; θÞ to the local standard deviation of noise σ ε ðr; θÞ. These local standard deviations are estimated from the autocorrelation function of the high-pass median filtered backscatter data, along the radial dimension (see Fig.…”

“…Wind estimates were retrieved from both instruments using the two motion estimation algorithms that were previously validated on the REAL against an independent Doppler lidar: cross-correlation (software named Gale) 19 and wavelet-based optical flow (software named Typhoon). 20 At the time of the side-by-side experiment, SAMPLE was not capable of quickly returning the telescope pointing direction to the starting angle of each scan, a move employed by the REAL beam steering unit and referred to as "fly-back." As a result, the SAMPLE swept the lidar beam back and forth in azimuth at the same rate while the REAL collected data only when scanning in one azimuthal direction and in between quick fly-backs.…”