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An output feedback observer-based dynamic surface controller is presented for attitude tracking problem of the quadrotor unmanned aerial vehicle, which is subject to measurement noise and external disturbances. The dynamics model of the quadrotor unmanned aerial vehicle is firstly introduced with the quaternion representation. Subsequently, a nonlinear augmented observer is introduced for simultaneously estimating the unavailable states and uncertain disturbances from the measurement of system output. The output feedback controller based on the nonlinear augmented observer is designed with the dynamic surface control technique. The Lyapunov stability analysis shows that the attitude tracking performance is ensured and all signals of the closed-loop system remain bounded. Finally, simulative and experimental results are carried out to illustrate, compared with other observer-based controller, the effectiveness of the proposed method is better. [ABSTRACT FROM AUTHOR]

This paper presents a new active disturbance rejection controller to solve the altitude and attitude control problem for a quadrotor unmanned aerial vehicle. The proposed method requires only the output information of the system. Using the pitch subsystem as an example, the proposed controller is designed by using dynamic surface control strategy incorporated with tracking differentiator, and extended state observer, which is used to estimate the uncertain disturbance. The estimate states of extended state observer are used to design the dynamic surface control law for altitude and attitude tracking problem of the quadrotor unmanned aerial vehicle. The stability analysis proves that a sufficient condition of the asymptotic stability of the extended state observer is achieved, the asymptotic stability of the closed-loop system can be guaranteed, and the tracking feedback error can made arbitrarily small by adjusting the controller parameters. Several simulation results are presented to corroborate that the proposed control method has better effectiveness and robustness. [ABSTRACT FROM AUTHOR]

To examine the effects of soil warming on carbon-accumulation and -release processes in the wetland ecosystem, a field-warming experiment was conducted under flooded and unflooded water conditions in the typical meadow Calamagrostis angustifolia (C. angustifolia) (TMC) wetland in the Sanjiang Plain, northeast China. Warming cables were used to simulate soil warming. Warming caused significant increases in aboveground biomass compared with belowground biomass during the growing season, and the enhancement of aboveground biomass increased with plant growth while belowground biomass showed an opposite effect. Significant positive correlation was found between aboveground biomass and 10-20-cm soil [image omitted] content whereas belowground biomass was more significantly correlated with 0-10-cm soil [image omitted] content. Positive linear correlations were found between CO2 and CH4 fluxes and warming-induced changes in liable carbon (LBC) and carbohydrate carbon (CHC) contents. Flooded water conditions tended to increase the accumulation of belowground biomass, [image omitted] content and CH4 fluxes under warming treatment. Soil warming could not only stimulate the carbon-accumulation and -release processes in the TMC wetland ecosystem directly, but also indirectly through the enhancement of nitrogen availability and active carbon contents. The contents of [image omitted] and active carbon could be sensitive indicators for the carbon-process changes in wetland ecosystems under soil warming. [ABSTRACT FROM AUTHOR]