First field measurements of optical turbulence near the ground with a newly developed fine-wire thermometer

First results of optical turbulence field measurements collected with a newly developed fine-wire temperature sensing system are presented and discussed. The centerpiece of the sensing system is an array of fine-wire platinum resistance thermometers. The active fine wire in each sensor element has a diameter of 0.64 μm and a length between 0.5 and 1 mm. The sampling rate is 44.1 kHz, and the noise level is 1 mK for a bandwidth of 10 kHz. Data were recorded while the car onto which the sensors were mounted was traveling at a speed of about 40 mph, or 18 m s−1. Estimates of the temperature structure function Dθθ(r) are compared against the classical Obukhov-Corrsin theory, which predicts rα power-law asymptotes with α=2 in the viscous-diffusive range and α=2/3 in the inertial-convective range. For the pair of separations r1=5 cm and r2=10 cm, we observed α=0.63±0.06. The frequency spectrum Sθθ(f) follows the theoretically predicted f−5/3 power law in the inertial-convective subrange. The ‘Hill bump’ in the transition regime between the inertial-convective and viscous-diffusive subranges is visible.