A novel method for destriping of OCM-2 data and radiometric performance analysis for improved ocean color data products

Despite the capability of Ocean Color Monitor aboard Oceansat-2 satellite to provide frequent, high-spatial resolution, visible and near-infrared images for scientific research on coastal zones and climate data records over the global ocean, the generation of science quality ocean color products from OCM-2 data has been hampered by serious vertical striping artifacts and poor calibration of detectors. These along-track stripes are the results of variations in the relative response of the individual detectors of the OCM-2 CCD array. The random unsystematic stripes and bandings on the scene edges affect both visual interpretation and radiometric integrity of remotely sensed data, contribute to confusion in the aerosol correction process, and multiply and propagate into higher level ocean color products generated by atmospheric correction and bio-optical algorithms. Despite a number of destriping algorithms reported in the literature, complete removal of stripes without residual effects and signal distortion in both low- and high-level products is still challenging. Here, a new operational algorithm has been developed that employs an inverted gaussian function to estimate error fraction parameters, which are uncorrelated and vary in spatial, spectral and temporal domains. The algorithm is tested on a large number of OCM-2 scenes from Arabian Sea and Bay of Bengal waters contaminated with severe stripes. The destriping effectiveness of this approach is then evaluated by means of various qualitative and quantitative analyses, and by comparison with the results of the previously reported method. Clearly, the present method is more effective in terms of removing the stripe noise while preserving the radiometric integrity of the destriped OCM-2 data. Furthermore, a preliminary time-dependent calibration of the OCM-2 sensor is performed with several match-up in-situ data to evaluate its radiometric performance for ocean color applications. OCM-2 derived water-leaving radiance products obtained after calibration show a good consistency with in-situ and MODIS-Aqua observations, with errors less than the validated uncertainties of ±5% and ±35% endorsed for the remote-sensing measurements of water-leaving radiance and retrieval of chlorophyll concentrations respectively. The calibration results show a declining trend in detector sensitivity of the OCM-2 sensor, with a maximum effect in the shortwave spectrum, which provides evidence of sensor degradation and its profound effect on the striping artifacts in the OCM-2 data products.     

Spatiotemporal variations in litter mass and their relationships with climate in temperate grassland: A case study from Xilingol grassland,Inner Mongolia (China)

Clarifying spatiotemporal variations of litter mass and their relationships with climate factors will advance our understanding of ecosystem structure and functioning in grasslands. Our objective is to investigate the spatiotemporal variations of litter mass in the growing season and their relationships with precipitation and temperature in the Xilingol grassland using MOD09A1 data. With widely used STI (simple tillage index), we firstly estimated the litter mass of Xilingol grassland in the growing season from 2000 to 2014. Then we investigated the variations of litter mass in the growing season at regional and site scales. We further explored the spatiotemporal relationships between litter mass and precipitation and temperature at both scales. The litter mass increased with increasing mean annual precipitation and decreasing mean annual temperature at regional scale. The variations of litter mass at given sites followed quadratic function curves in the growing season, and litter mass generally attained maximums between August 1 and September 1. Positive spatial relationship was observed between litter mass variations and precipitation, and negative spatial relationship was found between litter mass variations and temperature in the growing season. There was no significant relationship between inter-annual variations of litter mass and precipitation and temperature at given sites. Results illustrate that precipitation and temperature are important drivers in shaping ecosystem functioning as reflected in litter mass at regional scale in the Xilingol grassland. Our findings also suggest the action of distinct mechanism in controlling litter mass variations at regional and sites scales.     

Estimation of sediment settling velocity in estuarine and coastal waters using optical remote sensing data

A robust method has been developed for estimating sediment settling velocity (w_s) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (C_d), Reynolds number (Re), grain size (D₅₀), specific gravity (Δ_SG) and grain shape (in terms of the Corey Shape Factor – CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (b_bp), beam attenuation (c_p), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m?s^?1) varied from very low values in clear oceanic waters, intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with the field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.     

Multi-block SSD based on small object detection for UAV railway scene surveillance

A method of multi-block Single Shot MultiBox Detector (SSD) based on small object detection is proposed to the railway scene of unmanned aerial vehicle surveillance. To address the limitation of small object detection, a multi-block SSD mechanism, which consists of three steps, is designed. First, the original input images are segmented into several overlapped patches. Second, each patch is separately fed into an SSD to detect the objects. Third, the patches are merged together through two stages. In the first stage, the truncated object of the sub-layer detection result is spliced. In the second stage, a sub-layer suppression and filtering algorithm applying the concept of non-maximum suppression is utilized to remove the overlapped boxes of sub-layers. The boxes that are not detected in the main-layer are retained. In addition, no sufficient labeled training samples of railway circumstance are available, thereby hindering the deployment of SSD. A two-stage training strategy leveraging to transfer learning is adopted to solve this issue. The deep learning model is preliminarily trained using labeled data of numerous auxiliaries, and then it is refined using only a few samples of railway scene. A railway spot in China, which is easily damaged by landslides, is investigated as a case study. Experimental results show that the proposed multi-block SSD method produces an overall accuracy of 96.6% and obtains an improvement of up to 9.2% compared with the traditional SSD.     

轻小型高光谱成像仪前置望远系统设计

轻小型、高分辨率已经成为高光谱成像仪的发展趋势。文章基于Offner型光谱成像系统的结构特点,分析了高光谱成像仪前置望远系统的设计特殊性,利用同轴反射系统的几何光学理论求解方法,给出了一种长焦距、大视场的高光谱成像仪前置望远离轴三反远心系统的设计思路和设计结果,光学系统焦距2 500 mm,视场角达到12°。分析表明,该设计在奈奎斯特频率71.4线对/mm处调制传递函数接近衍射极限,结构紧凑,不仅适用于Offner型光谱仪前置望远光学系统,还可用于其它大视场远心光学系统。     

定量遥感有效载荷配置方法与发展

针对定量遥感这一广泛应用于气象、海洋与环境等领域卫星的遥感技术,分析了各个领域的应用需求。为了解决如何根据定量遥感的应用需求,快速配置有效载荷,并合理设置有效载荷的探测谱段(频段)这一制约卫星发展的关键问题。提出了从探测目标着手的方法,首先,分析满足探测要素所需的谱段设置、指标要求和有效载荷配置类型,得出了有效配置载荷的方法和思路;其次,以全球云探测为例,验证本方法的合理性;最后,分析定量遥感有效载荷的发展重点和发展方向,为气象、海洋与环境领域等定量遥感卫星的长期发展提供技术支撑。     

北京一号小卫星及其数据应用

结合小卫星技术介绍了北京一号高性能对地观测小卫星计划和项目进展情况,综述了北京一号系统的主要组成和性能,并结合其数据特点,介绍北京一号遥感影像的示范应用和重点应用,探讨、分析了其更广泛的应用领域和良好的市场前景。     

遥感系列卫星在轨微振动测量与分析

在遥感系列卫星上装载了微振动环境测量系统并进行了在轨微振动环境测量。文章介绍了4颗遥感卫星的在轨微振动环境参数获取与分析。结果表明:星上各活动部件中主要的扰振源为反作用轮和辐射计/散射计转动机构;卫星稳定运行时的最大微振动量级约为57 mg,传递到光学敏感设备衰减度约为15%。     

遥感图像云检测方法综述

遥感图像云检测是遥感数据处理过程中需首要解决的问题之一,在参考大量国内外文献的基础上,文章对遥感图像云检测方法的研究现状进行了分析,并对已有的遥感图像云检测方法进行了综述和分类,在此基础上对不同的云检测方法进行了比较,最后给出了云检测存在的问题和发展趋势.     

雷达对抗侦察中基于广义似然比检测的子带频谱检测算法

根据雷达对抗侦察接收信号的特点,提出了基于动态非均匀信道化滤波的接收结构.重点研究了其中的频谱感知环节,提出了基于广义似然比检测的子带频谱检测算法.该算法首先假设至少含有K个子带不存在信号,再根据K个子带输出估计噪声方差,从而给出了基于广义似然比检测的子带频谱检测算法的检验统计量.对于具有频率先验信息的重点目标,论文给出了基于广义似然比检测快速频谱检测算法.理论分析和仿真表明了算法的有效性.