- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Proximal remote sensing of tree physiology at northern treeline: Do late-season changes in the photochemical reflectance index (PRI) respond to climate or photoperiod?
摘要： Relatively little is known of how the world's largest vegetation transition zone – the Forest Tundra Ecotone (FTE) – is responding to climate change. Newly available, satellite-derived time-series of the photochemical reflectance index (PRI) across North America and Europe could provide new insights into the physiological response of evergreen trees to climate change by tracking changes in foliar pigment pools that have been linked to photosynthetic phenology. However, before implementing these data for such purpose at these evergreen dominated systems, it is important to increase our understanding of the fine scale mechanisms driving the connection between PRI and environmental conditions. The goal of this study is thus to gain a more mechanistic understanding of which environmental factors drive changes in PRI during late-season phenological transitions at the FTE – including factors that are susceptible to climate change (i.e., air- and soil-temperatures), and those that are not (photoperiod). We hypothesized that late-season phenological changes in foliar pigment pools captured by PRI are largely driven by photoperiod as opposed to less predictable drivers such as air temperature, complicating the utility of PRI time-series for understanding climate change effects on the FTE. Ground-based, time-series of PRI were acquired from individual trees in combination with meteorological variables and photoperiod information at six FTE sites in Alaska. A linear mixed-effects modeling approach was used to determine the significance (α = 0.001) and effect size (i.e., standardized slope b*) of environmental factors on late-seasonal changes in the PRI signal. Our results indicate that photoperiod had the strongest, significant effect on late-season changes in PRI (b* = 0.08, p < 0.001), but environmental variables susceptible to climate change were also significant (i.e., daily mean solar radiation (b* = ?0.03, p < 0.001) and daily mean soil temperature (b* = 0.02, p < 0.001)). These results suggest that interpreting PRI time-series of late-season phenological transitions may indeed facilitate our understanding of how northern treeline responds to climate change.
关键词： PRI,Climate change,Photoperiod,Photosynthetic phenology,MODIS,Solar radiation,Northern treeline,Forest Tundra Ecotone
更新于2025-09-23 15:21:21
-
[IEEE 2017 International Conference on Current Trends in Computer, Electrical, Electronics and Communication (CTCEEC) - Mysore, India (2017.9.8-2017.9.9)] 2017 International Conference on Current Trends in Computer, Electrical, Electronics and Communication (CTCEEC) - Mitigation of Lower Order Harmonics in a Grid-Connected Single-Phase PV Inverter using Shunt Active Filter
摘要： In this paper, a novel technique is proposed for mitigating lower order harmonics for single phase PV inverter using harmonic compensation. Step up transformer is used boost the voltage as per requirement of the grid. However, the implemented system will not introduce any lower order harmonics in the grid, but there are little chances of lower order harmonics, because of the dead time of inverter, core saturation and magnetizing current of the transformer, etc. In this paper, a unique approach is being presented which mitigates lower order harmonics using inverter current control. In this paper, adaptive harmonic compensation technique with additional active filter is being presented before feeding a supply to the grid. To obtain better control proportional resonant integral (PRI) controller is integrated. The advantage of using PRI controller is; it eliminates DC component from the control loop. In this paper, a PRI controller and LMS adaptive harmonic filter are also been discussed in great detail. In this paper, two systems are considered and compared one with an adaptive harmonic filter using SPWM, and in the second system, active filter is added before feeding inverter output to the step up transformer. Hence the first system is explained in great detail and for second system illustration of the active filter and obtained results are compared.
关键词： LMS adaptive filter,single phase PV inverter,harmonic distortion,PRI controller
更新于2025-09-09 09:28:46