Laser Doppler Data Processing

Techniques - Transit-Time Weighting

Transit-time weighting (also known as residence-time weighting) with

where $w_i$ is the weighting factor for the $i$-th sample and ${\tau }_i$ is the transit time (or residence time) of the appropriate particle through (or in) the measurement volume, is the only weighting scheme that has been found to be reliable enough to be widely accepted by the community. This holds even though the transit time introduces another random value into the signal processing. This is because the measured transit time depends on the particle's path through the measurement volume. The only problem in practical applications has been the slow adoption by commercial manufacturers. The situation has significantly improved in the recent years as the importance of reliable transit time measurements has been slowly recognized.

original paper:

• Hösel W and Rodi W (1977): New Biasing Elimination Method for Laser-Doppler-Velocimeter Counter Processing. Rev. Sci. Instrum. 48, 7, 910-919

review papers:

• Buchhave P, George Jr W K and Lumley J L (1979): The Measurement of Turbulence with the Laser Doppler Anemometer. Annual Review of Fluid Mechanics 11, 442-503, Annual Reviews, Inc., Palo Alto, CA
• Edwards R V (1987): Report of the Special Panel on Statistical Partical Bias Problems in Laser Anemometry. Transactions of the ASME, Journal of Fluids Engineering 109, 89-93

overview and comparison:

• Damaschke N, Kühn V, Nobach H (2018): A Fair Review of Non-parametric Bias-free Autocorrelation and Spectral Methods for Randomly Sampled Data in Laser Doppler Velocimetry. Digital Signal Processing, 76, 22-33