Interference fringes on GLORIA side-scan sonar images from the Bering Sea and their implications

GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea.     

光栅栅距检测与线阵CCD细分技术研究

利用线阵CCD分辨率高、像素均匀等特点对光栅莫尔条纹进行细分是目前广泛采用的一种新技术。由于CCD具有自扫描能力，能将光强随空间分布的莫尔条纹信号转换成随时间变化的电信号，从而可以对光栅刻线的像的移动进行精确定位和直接数字化，改变传统莫尔条纹位相细分方法，实现对光栅栅距进行高倍数的细分。     

Using InSAR to identify hydrological connectivity and barriers in a highly fragmented wetland

Hydrological connectivity is a critical determinant of wetland functions and health, especially in wetlands that have been heavily fragmented and regulated by human activities. However, investigating hydrological connectivity in these wetlands is challenging due to the costs of high-resolution and large-scale monitoring required in order to identify hydrological barriers within the wetlands. To overcome this challenge, we here propose an interferometric synthetic aperture radar (InSAR)-based methodology to map hydrologic connectivity and identify hydrological barriers in fragmented wetlands. This methodology was applied along 70 transects across the Baiyangdian, the largest freshwater wetland in northern China, using Sentinel 1A and 1B data, covering the period 2016–2019. We generated 58 interferograms providing information on relative water level changes across the transects that showed the high coherence needed for the assessment of hydrological connectivity. We mapped the permanent and conditional (temporary) barriers affecting connectivity. In total, 11% of all transects are permanently disconnected by hydrological barriers across all interferograms and 58% of the transects are conditionally disconnected. Areas covered by reed grasslands show the most undisturbed hydrological connectivity while some of these barriers are the result of ditches and channels within the wetland and low water levels during different periods of the year. This study highlights the potential of the application of Wetland InSAR to determine hydrological connectivity and location of hydrological barriers in highly fragmented wetlands, and facilitates the study of hydrological processes from large spatial scales and long-time scales using remote sensing technique.     

城市边缘区土地利用结构分形特征的动态变化——以广州市南拓区为例

近20年来,随着广州市城市化水平的大幅提升,作为城市地域空间发展前沿的城市边缘区土地利用变化异常明显.本文以广州市典型城市边缘区为研究对象,基于覆盖广州市南拓区的4时相TM遥感解译数据,构建土地利用数量结构变化模型和分形结构模型,定量化研究区域土地利用结构的变化强度、复杂性和稳定性.研究结果表明:在广州市核心区城市化辐...     

绝对重力仪双采样过零检测中量化噪声的影响分析

利用高速采集系统完整记录绝对重力仪棱镜自由下落的干涉条纹波形,能够获取更多的重力信息。详细讨论了干涉条纹电压信号幅值与ADC相关参数,如等效位数、参考电压、采样频率等对重力测量的影响。结果表明,通过参数优化设计可以将ADC量化的影响限制在0.01 μGal。     

中国大城市边缘区特性研究

本文通过北京、上海、广州、南京等大城市调查,在探讨中国城市边缘区划分的基础上,对中国大城市边缘区的人口特性、社会特性、经济特性、土地利用特性以及地域空间特性进行了研究。     

温度对POP Rb原子钟性能影响的研究

从温度对缓冲气体碰撞频移和弛豫率的影响出发,对充有Ar和N2这2种缓冲气体的POP(pulsed optically pumped,脉冲激光抽运)汽泡式铷原子钟的温度特性进行了理论和实验研究。研究表明,Ar与N2的气压比为1.6时,60℃的线性温度系数为0;不同温度时,布居数差弛豫率1和相干弛豫率2各不相同,若1 2,则POP铷原子钟Ramsey条纹包络在微波场与原子跃迁失谐为0附近为凹陷,信噪比较差,反之,为凸起,信噪比较高。研究结果对设计POP原子钟的缓冲气体气压比和工作温度,以及提高POP原子钟的中长期稳定度有一定借鉴作用。     

基于Fabry-Perot的中高层大气风速反演数据处理研究

中高层大气风速反演需要精确的确定法布里-帕罗干涉仪(Fabry-Perot Interferometer,FPI)干涉条纹的圆心和半径.本文针对FPI非闭合式干涉环条纹,提出了新的条纹圆心和半径确定方法:首先对所得到的条纹强度分布进行噪声去除预处理:包括均值滤波和自适应滤波;然后初步确定圆心,以该圆心为中心作n条射线得到n条干涉环剖线,利用高斯函数拟合得到干涉环峰值位置,再利用所得峰值位置进行圆拟合得到新的圆心和半径;最后以新的圆心为初始圆心重复上述计算过程直到圆心坐标收敛.利用上述方法对FPI仿真数据进行处理,并用于中高层大气风速反演,得到风速值为96.9537 m/s(对应实际风速值约100 m/s)和7.528.2 m/s (对应实际风速值约10 m/s),将其与理论实际值进行比较,得到反演绝对误差分别为-2.977 m/s和-2.465 m/s,相对误差分别为-2.98%和-24.67%,表明上述方法满足中高层大气风速(一般为每秒几十米到几百米)的反演精度要求,初步论证了圆心和半径确定方法的可行性.     

城市边缘区居住用地的空间异质性:构型、度量与低熵化

基于对城市边缘区居住用地演进模式的研究,采用信息熵定量研究城市边缘区居住用地的空间分异性状,并构建相应的改造模式。结果表明,城市边缘区居住用地有其自身的复杂性和多变性,其存在的空间分异可以用信息熵进行度量,基于度量结果,将其分为4种类型。这些类型的土地利用状态呈现不同的特点,根据其特点分别设计相应的模式对其进行低熵化改造,以实现土地高效、合理及可持续利用目标。     

城市边缘区的绿色城市设计理念与方法

城市边缘区作为一个特殊区域,在城市化的快速推进中,呈现着城乡复合、动态多变的发展特征.由于多方面原因.城市边缘区在社会环境和自然空间环境方面还存在着较多的问题.要使城市边缘区和谐、健康发展,在规划建设中,必须遵循绿色城市设计的理念与原则,运用基于城市边缘区特征的、结合自然生态环境的城市设计方法,构建人性化的居住和公共空间,创造城市与农村多功能相互协调、多种价值体系综合优化的空间环境.