Optimal video communication strategy for intelligent video analysis in unmanned aerial vehicle applications

For Unmanned Aerial Vehicles (UAV), the intelligent video analysis is a key technology in intelligent autonomous control, real-time navigation and surveillance. However, poor UAV wireless links would degrade the quality of video communication, leading to difficulties in video analysis. To meet the challenges of packet-loss and limited bandwidth in adverse UAV channel environments, this paper proposes a parameter optimization mechanism for UAV intelligent video analysis. In the proposed method, an Optimal Strategy Library (OSL) is designed to optimize the parameters for video encoding and forward error correction. Adapted to the packet-loss rate and bandwidth in practical UAV wireless network, the proposed OSL can facilitate the encoding of video sequences and the recovery of degraded videos with optimal performance. Experimental results demonstrate that the proposed solution can keep intelligent video analysis working efficiently with adverse UAV wireless links, and is capable of maximizing the inference accuracy of Multi-Object Tracking (MOT) algorithms in various scenarios.     

NeQuick G model based scale factor determination for using SBAS ionosphere corrections at low earth orbit

A space-based augmentation system (SBAS) provides real-time correction data for global navigation satellite system (GNSS) users near ground. In order to use the SBAS ionosphere correction for low Earth orbit (LEO) satellites, the correction should be scaled down for the LEO altitude. This scale factor varies with ionosphere distribution and it is hard to determine the value at LEO in real time. We propose a real-time scale factor determination method by using Galileo GNSS’s NeQuick G model. A LEO satellite GPS data and SBAS data received on ground were used to evaluate the performance of the NeQuick G derived variable scale factor. The NeQuick G derived scale factor shows a significant accuracy improvement over NeQuick G model or pre-determined constant scale factor. It improves a vertical positioning accuracy of the LEO satellite. The error mean reductions of the vertical positioning over NeQuick G and the constant scale factor are 31.5% and 11.7%, respectively.     

The use of MODIS 250 m bands to improve the MODIS 1 km ocean color atmospheric correction algorithm in turbid water

“Clear water” is a scale-dependent concept, so it is more likely to successfully find the “clear water” from images with smaller scale than that with larger scale data. In this study, an optimal spectral relationship of moderate-resolution imaging spectroradiometer (MODIS) 250 m and 1 km resolution data at near-infrared bands (OSRLM) is constructed for converting pseudo “clear water” reflectance at 859 nm to those at 748 and 869 nm. According to scale effects, the satellite-observed pseudo “clear water” reflectance is greater than 5.18%, larger than that derived from OSRLM model. An atmospheric correction model for MODIS 1km data using pseudo “clear water” reflectance of MODIS 250 m data (ACMM) was developed for improving the performance of traditional “clear water” atmospheric correction model (CWAC). The model validation results indicate that ACMM model has a better performance than CWAC model. By comparison, the uncertainty decreases by 19.18% in the use of ACMM model over CWAC model for deriving water-leaving reflectance in Taihu Lake, China. This uncertainty is significantly reduced in water-leaving reflectance estimation due to partial removal of scale effects on “clear water”. These findings imply that satellite-derived aerosol scattering contribution at smaller scale usually has a better performance than that at larger scale.     

An estimation of tropospheric corrections using GPS and synoptic data: Improving Urmia Lake water level time series from Jason-2 and SARAL/AltiKa satellite altimetry

Tropospheric correction is one of the most important corrections in satellite altimetry measurements. Tropospheric wet and dry path delays have strong dependence on temperature, pressure and humidity. Tropospheric layer has particularly high variability over coastal regions due to humidity, wind and temperature gradients. Depending on the extent of water body and wind conditions over an inland water, Wet Tropospheric Correction (WTC) is within the ranges from a few centimeters to tens of centimeters. Therefore, an extra care is needed to estimate tropospheric corrections on the altimetric measurements over inland waters. This study assesses the role of tropospheric correction on the altimetric measurements over the Urmia Lake in Iran. For this purpose, four types of tropospheric corrections have been used: (i) microwave radiometer (MWR) observations, (ii) tropospheric corrections computed from meteorological models, (iii) GPS observations and (iv) synoptic station data. They have been applied to Jason-2 track no. 133 and SARAL/AltiKa track no. 741 and 356 corresponding to 117–153 and the 23–34 cycles, respectively. In addition, the corresponding measurements of PISTACH and PEACHI, include new retracking method and an innovative wet tropospheric correction, have also been used. Our results show that GPS observation leads to the most accurate tropospheric correction. The results obtained from the PISTACH and PEACHI projects confirm those obtained with the standard SGDR, i.e., the role of GPS in improving the tropospheric corrections. It is inferred that the MWR data from Jason-2 mission is appropriate for the tropospheric corrections, however the SARAL/AltiKa one is not proper because Jason-2 possesses an enhanced WTC near the coast. Furthermore, virtual stations are defined for assessment of the results in terms of time series of Water Level Height (WLH). The results show that GPS tropospheric corrections lead to the most accurate WLH estimation for the selected virtual stations, which improves the accuracy of the obtained WLH time series by about 5%.     

民用飞机机身蒙皮对接结构疲劳分析及试验

在对细节疲劳额定值(DFR)方法深入研究的基础上,对 MA700飞机机身蒙皮典型对接结构进行了疲劳寿命分析,确定了该结构的载荷传递及一系列修正系数,得到了结构疲劳寿命分析结果.     

Navigation message designing with high accuracy for NAV

Navigation message designing with high accuracy guarantee is the key to efficient navigation message distribution in the global navigation satellite system（GNSS）. Developing high accuracy-aware navigation message designing algorithms is an important topic. This paper investigates the high-accuracy navigation message designing problem with the message structure unchanged.The contributions made in this paper include a heuristic that employs the concept of the estimated range deviation（ERD） to improve the existing well-known navigation message on L1 frequency（NAV） of global positioning system（GPS） for good accuracy service; a numerical analysis approximation method（NAAM） to evaluate the range error due to truncation（RET） of different navigation messages; and a basic positioning parameters designing algorithm in the limited space allocation. Based on the predicted ultra-rapid data from the ultra-rapid data from the international GPS service for geodynamic（IGU）, ERDs are generated in real time for error correction.Simulations show that the algorithms developed in this paper are general and flexible, and thus are applicable to NAV improvement and other navigation message designs.     

伞舱系统跟踪引导数据迭代算法

针对在返回舱乘伞下降阶段,测控链中弹道测量设备丢失目标,以及跟踪结束后无法外推生成可靠引导数据,光学设备难以快速捕获目标等问题,以风场修正模型为基础,通过风场提前修正与采用测量数据实际修正相结合的方法,建立伞舱系统跟踪引导数据迭代算法.利用多次返回段任务数据对该算法进行实验验证,并与实际任务中目前使用的方法进行比较,结果表明：通过该算法推算较长时间后的引导数据,其平均误差为现有方法的6％;推算较短时间后的引导数据,其平均误差为现有方法的20％.因此,利用该算法计算的引导数据精度较高,有助于光学设备及其他测控设备快速捕获或重捕目标.     

电压变化时Boost PFC变换器的混沌和分叉现象

利用小信号模型对开关电源控制器进行设计过程中常出现混沌分叉等不稳定现象。以工程设计的角度,建立了平均电流型BoostPFC的精确电路模型,分析了系统中存在的非线性现象,结合非线性分叉和混沌理论对这类非线性现象进行了详细的分析和推导。     

基于修正角模型的平显工作状态仿真研究

研究了在某型平显仿真训练器中实现平显工作状态仿真的方法。首先介绍了平显工作画面,分析了瞄准环及其构成修正角的原理;然后通过对工作式和各相关参数的计算,建立了平显的瞄准环及其修正角的模型,并给出了计算瞄准环环心位置和直径的基本关系式;最后讨论了用VisualC++编程实现平显工作画面中公共符号和瞄准环仿真的方法。通过建立修正角模型,可使实现的平显仿真工作画面在外观上和操作特性上与实际平显工作状态一致。     

RESEARCH ON THE METHODS OF IMPROVING DGPS POSITIONING PRECISION

A DGPS positioning model is described, and the elements that influence DGPS positioning precision are analyzed in detail. On this basis, the methods of improving DGPS positioning precision are proposed which include increasing updating rate of DGPS correction, building extended DGPS system and improving quality of DGPS correction signal. In the intelligent monitor and control system of the public transport in Beijing, these methods improve the vehicle positioning precision to 2～5m.