Air turbulence has become a major cause of significant injuries and aircraft damages. We are pursuing the research and development of a practical airborne Doppler LIDAR that will detect air turbulence ahead of an aircraft in-flight and give advanced warning to pilots. Although a larger measurement range could be achieved by using higher powered laser, it implies larger and heavier devices which are not favorable for airborne applications. We use a wind velocity width to detect air turbulence and introduce a spectral fitting method which reduces measurement errors of the wind velocity width and extends the measurement range. This paper describes the effect of the detection of air turbulence using the wind velocity width estimated by the spectral fitting method.
We are pursuing the research and development of a practical airborne Doppler LIDAR that will detect air turbulence which is a major cause of significant injuries and aircraft damages. Although a longer detection range of air turbulence could be achieved by using higher powered laser to give advanced warning to crew and passengers, it implies larger and heavier devices which are not suitable for airborne applications. We introduce a colored noise reduction method which reduces the measurement errors and extends the measurement range for the air turbulence detection. We show that the detection range of air turbulence is improved by about 40% using the colored noise reduction method.
SUMMARYA scheme that estimates and compensates for the frequency offset from the phase rotation of pilot symbols is proposed as a carrier frequency offset compensation scheme that periodically inserts pilot symbols in the transmitted signal. Since the frequency offset is estimated and compensated for at a frequency close to the direct path wave when a conventional scheme is applied in a Rician fading environment where the direct path wave is Doppler shifted, the Doppler spread appears to widen further, the estimation error of the fading distortion increases, and the error rate performance degrades. In this paper, we propose a frequency offset compensation scheme that estimates the center frequency of the Doppler spread and reduces the effects of the Doppler-shifted direct path wave by (1) calculating the signal power in the frequency domain by taking the discrete Fourier transform (DFT) of the pilot symbols and (2) smoothing the signal power in a frequency window. Computer simulations demonstrate the superior error rate performance of the proposed scheme compared to the conventional scheme and clearly show its effectiveness.
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