3D-calibration of three- and four-sensor hot-film probes based on collocated sonic using neural networks

Abstract

High resolution measurements of turbulence in the atmospheric boundary layer (ABL) are critical to the understanding of physical processes and parameterization of important quantities, such as the turbulent kinetic energy dissipation. Low spatio-temporal resolution of standard atmospheric instruments, sonic anemometers and LIDARs, limits their suitability for fine-scale measurements of ABL. The use of miniature hot-films is an alternative technique, although such probes require frequent calibration, which is logistically untenable in field setups. Accurate and truthful calibration is crucial for the multi-hot-films applications in atmospheric studies, because the ability to conduct calibration in situ ultimately determines the turbulence measurements quality. Kit et al (2010 J. Atmos. Ocean. Technol. 27 23-41) described a novel methodology for calibration of hot-film probes using a collocated sonic anemometer combined with a neural network (NN) approach. An important step in the algorithm is the generation of a calibration set for NN training by an appropriate low-pass filtering of the high resolution voltages, measured by the hot-film-sensors and low resolution velocities acquired by the sonic.

Next generation combined sonic-hotfilm anemometer: wind alignment and automated calibration procedure using deep learning

“…The transfer function can either be computed for each x-probe separately while averaging the redundant 𝑢 component or to be constructed using 4 voltage inputs with 3 velocity outputs. Kit and Liberzon (2016) (Kit and Liberzon 2016) already demonstrated that neither is superior to the other and we confirm this result. Finally, as the hotfilms gradually degrade with use resulting in measurement drift, the traditional jet-based calibration was performed twice.…”

“…NN have also successfully been used for complex function approximations. Several studies have shown that regression NN are capable of capturing the velocity-voltage relationship estimates strikingly well in hotwire anemometry (Kit and Grits 2011;Fernando et al 2015;Kit and Liberzon 2016;Kit et al 2017;Goldshmid and Liberzon 2018). In these studies, the training set (TS) used for each model was based on delicately selected minutes that contained mean velocities that covered the entire range of interest and high rms values of velocity fluctuations.…”

“…The motivation of the selection of two x-probes was mostly economical and based on Kit and Liberzon (2016) (Kit and Liberzon 2016), where two x-probes are oriented 90 degrees from each other to provide the complete 3D flow components. Each xprobe captures two components of the velocity field, and since they are oriented at a 90° (in the roll axis) relative to each other, all three components are captured.…”

“…(Oncley et al 1996;Poulos et al 2006). In-situ calibration was later implemented several times in the laboratory to demonstrate its capabilities (Kit and Liberzon 2016), (Kit et al 2010) and many times in the field (Kit and Grits 2011;Fernando et al 2015;Kit and Liberzon 2016;Kit et al 2017;Goldshmid and Liberzon 2018). The studies in the laboratory presented the ability to use the simultaneously measured low frequency signal form the sonic to calibrate the high frequency signal of the hotfilm by means of least squares polynomial fitting and training artificial neural networks (NN).…”

“…The collocated sonic-hotfilm anemometer, dubbed the combo probe, was designed to overcome this hurdle, Figure 1. Developed and implemented in several field setups during the last decade (Kit et al 2010(Kit et al , 2017Kit and Grits 2011;Vitkin et al 2014;Kit and Liberzon 2016;Goldshmid and Liberzon 2018), the combo probe is capable of continuously sensing the fine-scales of turbulent fluctuations in the field, without the need for human interaction for frequent cumbersome re-calibrations. Consisting of a collocated sonic and two x-shaped double sensor hotfilm probes, the combo simultaneously samples the hotfilms and sonic at a high sampling frequency of several kilohertz.…”