High Performance Both in Low-Speed Tracking and Large-Angle Swing Scanning Based on Adaptive Nonsingular Fast Terminal Sliding Mode Control for a Three-Axis Universal Inertially Stabilized Platform.

In order to improve the performance in the practical engineering applications including so called low-speed video tracking and large-angle swing scanning imaging at the same time for a three-axis universal inertially stabilized platform (UISP), we propose an adaptive nonsingular fast terminal sliding mode control (ANFTSMC) strategy subjected to the uncertain disturbances and input saturation constraints. First of all, a second-order dynamic model is established with uncertain disturbances and input saturation constraints. Secondly, a nonsingular fast terminal sliding mode controller (NTSMC) is constructed to ensure the system error converges to zero fast in a finite time; meanwhile, a novel reaching law based on a modified normal distribution function is designed to adjust the control gain. Thirdly, an adaptive control law is designed to online estimate the parameters of the lumped uncertain disturbances. Additionally, the stability of the control system is proved by Lyapunov theory. Finally, extensive comparative simulations and experiments are carried out, the results comprehensively show the effectiveness and superiority of the proposed control method, which can accelerate convergence, weaken the chattering, and has the better control accuracy and robust performance both in the low-speed tracking and large-angle swing scanning applications. Moreover, the exact dynamic model and the prior knowledge of the upper bounds of the disturbances are not required during the procedure of the controller design, which make it have more extensive application value in practical engineering.

Relationship between the charge-coupled device signal-to-noise ratio and dynamic range with respect to the analog gain.

The signal-to-noise ratio and the dynamic range are the two key parameters characterizing CCD performance, especially in remote sensing applications. After exploring the possible sources of CCD noise, this paper analyzes the impacts of the analog gain on the two parameters, respectively, and establishes the mathematical models describing their relationships. Then the platforms including the CCD radiometric calibration and imaging in practice are constructed to test the proposed models based on two situations, considering the influence of the quantization noise. Finally, the design trade-off between the signal-to-noise ratio and the dynamic range is presented, such that the CCD signal-to-noise ratio will be improved as much as possible, while the dynamic range degradation becomes acceptable.

Clocking smear analysis and reduction for multi phase TDI CCD in remote sensing system.

Clocking smear caused by charge transfer of time delay and integration charge coupled device (TDI CCD) is the natural component in remote imaging sensing system, and it could not be eliminated by traditional motion compensation schemes. After researching on the operation of a typical three phase TDI CCD, we give a thorough understanding on causes of clocking smear. Then an elaborate mathematical model describing the charge transfer procedure is developed, and the modulation transfer function (MTF) losses due to charge transfer is also presented, which shows that nearly one pixel smear will be introduced by traditional phase timing. Therefore we propose a novel charge transfer method, using which only 1/2ϕ pixel smear will occur within the imaging operation of a single TDI stage, where ϕ represents the number of timing phases. Finally, a series of image simulations are made for two, three and four phase TDI CCD in which clocking smear is caused by our and conventional charge transfer methods respectively. The experimental results confirm that image quality improvement can be achieved by our method.

[High speed transmission system for dual-spectral remote sensing system].

In order to realize dual-spectral aerial camera image data transmission, a novel optical transmission system is proposed, then transmission scheme, structure of data frame and timing recovery method are discussed thoroughly. First, valid data in one line are picked up from two detectors before transmitting, a timing recovery method which makes in-out data timing and format consistent, is proposed using line valid interrupt flag. Second, based on transmitting and receiving buffering mechanism, dual asynchronous detectors data are transmitted in a single fiber. Third, transmitting and receiving systems are implemented using large programmable devices which embeds high speed data interface. Finally, behavioral and system verification method is proposed as well. Experimental results indicate that the system could support full, median and base cameral link protocol, serial data transmitting speed could be 6.25 Gb x s(-1), and pixel data rate is 40 MHz at most for two detectors. It is very suitable for space and serial remote sensing equipment due to its compact and high reliable structure.

An Fe stabilized metallic phase of NiS2 for the highly efficient oxygen evolution reaction.

This work reports a fundamental study on the relationship of the electronic structure, catalytic activity and surface reconstruction process of Fe doped NiS2 (FexNi1-xS2) for the oxygen evolution reaction (OER). A combined photoemission and X-ray absorption spectroscopic study reveals that Fe doping introduces more occupied Fe 3d6 states at the top of the valence band and thereby induces a metallic phase. Meanwhile, Fe doping also significantly increases the OER activity and results in much better stability with the optimum found for Fe0.1Ni0.9S2. More importantly, we performed detailed characterization to track the evolution of the structure and composition of the catalysts after different cycles of OER testing. Our results further confirmed that the catalysts gradually transform into amorphous (oxy)hydroxides which are the actual active species for the OER. However, a fast phase transformation in NiS2 is accompanied by a decrease of OER activity, because of the formation of a thick insulating NiOOH layer limiting electron transfer. On the other hand, Fe doping retards the process of transformation, because of a shorter Fe-S bond length (2.259 Å) than Ni-S (2.400 Å), explaining the better electrochemical stability of Fe0.1Ni0.9S2. These results suggest that the formation of a thin surface layer of NiFe (oxy)hydroxide as an active OER catalyst and the remaining Fe0.1Ni0.9S2 as a conductive core for fast electron transfer is the base for the high OER activity of FexNi1-xS2. Our work provides important insight and design principle for metal chalcogenides as highly active OER catalysts.