Natural and human-induced changes may exert considerable impacts on the seasonal and nodal dynamics of M2 and K1 tidal constituents.Therefore,quantifying the influences of these factors on tidal regime changes is esse...Natural and human-induced changes may exert considerable impacts on the seasonal and nodal dynamics of M2 and K1 tidal constituents.Therefore,quantifying the influences of these factors on tidal regime changes is essential for sustainable water resources management in coastal environments.In this study,the enhanced harmonic analysis was applied to extract the seasonal variability of the M2 and K1 tidal amplitudes and phases at three gauging stations along Lingdingyang Bay of the Zhujiang River Delta.The seasonal dynamics in terms of tidal wave celerity and amplification/damping rate were used to quantify the impacts of human-induced estuarine morphological alterations on M2 and K1 tidal hydrodynamics in inner and outer Lingdingyang Bay.The results show that both tidal amplification/damping rate and wave celerity were considerably increased from the pre-anthropogenic activity period(Pre-AAP)to the post-anthropogenic activity period(Post-AAP)excepting the tidal amplification/damping rate in outer Lingdingyang Bay,and the variations in outer Lingdingyang Bay was larger than those in inner Lingdingyang Bay.The alterations in these two parameters were more significant in flood season than in dry season in both inner and outer Lingdingyang Bay.The seasonal variability of M2 and K1 tidal amplitudes were further quantified using a regression model accounting for the 18.61-year lunar nodal modulation,where this study observes a considerable alteration in M2 constituent owing to human interventions.During the Post-AAP,the M2 amplitudes at the downstream station were larger than those that would have occurred in the absence of strong human interventions,whereas the opposite was true for the upstream station,leading to a substantial decrease in tidal amplification in outer Lingdingyang Bay.However,it is opposite in inner Lingdingyang Bay.The underlying mechanism can be primarily attributed to channel deepening and narrowing caused by human interventions,that resulted in substantial enlargement of the bay volume and reduced the effective bottom friction,leading to faster wave celerity and stronger amplified waves.展开更多
A broadband T/R frond-end of active holographic imaging system is presented. Compact autodyne mode circuit structure front-end is adopted to achieve higher signal to noise ratio and higher reliability, which is benefi...A broadband T/R frond-end of active holographic imaging system is presented. Compact autodyne mode circuit structure front-end is adopted to achieve higher signal to noise ratio and higher reliability, which is beneficial to the after-end imagining. The factors that influence the dynamic range and the transverse resolution ratio of holographic imaging system have been analyzed. Wide-band oscillator, wide-band low noise amplifier and the tapered slot antennas are implemented to meet the requirements of the holographic imagining system. According to the measured results, the output power is uniform in the broadband working frequency. The sub-harmonic suppression is better than 25 dBc from the frequency of 28 GHz to 33 GHz. The isolation between antennas channel is greater than 20 dB. The experimental result shows that the performance of the front-end is good enough to meet the needs of active millimeter-wave holographic imaging system.展开更多
基金The National Key R&D Program of China under contract No.2016YFC0402600the National Natural Science Foundation of China under contract No.51979296the Guangzhou Science and Technology Program of China under contract No.202002030452。
文摘Natural and human-induced changes may exert considerable impacts on the seasonal and nodal dynamics of M2 and K1 tidal constituents.Therefore,quantifying the influences of these factors on tidal regime changes is essential for sustainable water resources management in coastal environments.In this study,the enhanced harmonic analysis was applied to extract the seasonal variability of the M2 and K1 tidal amplitudes and phases at three gauging stations along Lingdingyang Bay of the Zhujiang River Delta.The seasonal dynamics in terms of tidal wave celerity and amplification/damping rate were used to quantify the impacts of human-induced estuarine morphological alterations on M2 and K1 tidal hydrodynamics in inner and outer Lingdingyang Bay.The results show that both tidal amplification/damping rate and wave celerity were considerably increased from the pre-anthropogenic activity period(Pre-AAP)to the post-anthropogenic activity period(Post-AAP)excepting the tidal amplification/damping rate in outer Lingdingyang Bay,and the variations in outer Lingdingyang Bay was larger than those in inner Lingdingyang Bay.The alterations in these two parameters were more significant in flood season than in dry season in both inner and outer Lingdingyang Bay.The seasonal variability of M2 and K1 tidal amplitudes were further quantified using a regression model accounting for the 18.61-year lunar nodal modulation,where this study observes a considerable alteration in M2 constituent owing to human interventions.During the Post-AAP,the M2 amplitudes at the downstream station were larger than those that would have occurred in the absence of strong human interventions,whereas the opposite was true for the upstream station,leading to a substantial decrease in tidal amplification in outer Lingdingyang Bay.However,it is opposite in inner Lingdingyang Bay.The underlying mechanism can be primarily attributed to channel deepening and narrowing caused by human interventions,that resulted in substantial enlargement of the bay volume and reduced the effective bottom friction,leading to faster wave celerity and stronger amplified waves.
文摘A broadband T/R frond-end of active holographic imaging system is presented. Compact autodyne mode circuit structure front-end is adopted to achieve higher signal to noise ratio and higher reliability, which is beneficial to the after-end imagining. The factors that influence the dynamic range and the transverse resolution ratio of holographic imaging system have been analyzed. Wide-band oscillator, wide-band low noise amplifier and the tapered slot antennas are implemented to meet the requirements of the holographic imagining system. According to the measured results, the output power is uniform in the broadband working frequency. The sub-harmonic suppression is better than 25 dBc from the frequency of 28 GHz to 33 GHz. The isolation between antennas channel is greater than 20 dB. The experimental result shows that the performance of the front-end is good enough to meet the needs of active millimeter-wave holographic imaging system.
