The NASA dual-frequency, dual-polarization, Doppler radar (D3R) is a weather radar operating at 13.91 GHz (Ku-band) and 35.56 GHz (Ka-band). The operational range of the D3R is 40 km, this relatively short operating r...
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ISBN:
(纸本)9781509049516
The NASA dual-frequency, dual-polarization, Doppler radar (D3R) is a weather radar operating at 13.91 GHz (Ku-band) and 35.56 GHz (Ka-band). The operational range of the D3R is 40 km, this relatively short operating range, along with the high sensitivity of D3R, are susceptible to increased observation of range ambiguous echoes, also referred to as "second-trip echoes". In this work, by leveraging a staggered pulse repetition period and random transmitted phase codes, two methods are developed to detect and dealias the second trip contamination for the operational use with the D3R. Using these methods, the overlapping echoes are separated, and unambiguous range of the D3R is increased. Weather signals are simulated and used to quantitatively characterize the performance of moment estimator over a wide range of realistic weather scenarios. The D3R's Ku-band observations are presented to demonstrate the performance of algorithm with and without overlapping echoes from different ranges.
In order to acquire an accurate three-dimensional (3D) measurement, the traditional fringe projection technique applies complex and laborious procedures to compensate for the errors that exist in the vision system. Ho...
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In order to acquire an accurate three-dimensional (3D) measurement, the traditional fringe projection technique applies complex and laborious procedures to compensate for the errors that exist in the vision system. However, the error sources in the vision system are very complex, such as lens distortion, lens defocus, and fringe pattern nonsinusoidality. Some errors cannot even be explained or rendered with clear expressions and are difficult to compensate directly as a result. In this paper, an approach is proposed that avoids the complex and laborious compensation procedure for error sources but still promises accurate 3D measurement. It is realized by the mathematical model extension technique. The parameters of the extended mathematical model for the 'phase to 3D coordinates transformation' are derived using the least-squares parameter estimation algorithm. In addition, a phase-coding method based on a frequency analysis is proposed for the absolute phase map retrieval to spatially isolated objects. The results demonstrate the validity and the accuracy of the proposed flexible fringe projection vision system on spatially continuous and discontinuous objects for 3D measurement.
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