测绘专业英语翻译31单元

Unit 31 Interferometric SAR (In SAR) Introduction 干涉雷达(SAR)介绍

Radar interferometry is a technique for extracting three-dimensional information of the Earth’s surface by using the phase content of radar signal as an additional information source derived from the complex radar data. I t was first used in observation of the surface of Venus and the Mo on.

雷达干涉测量技术中提取三维信息的地球表面的利用雷达信号的相位内容作为额外的信息源来自复杂的雷达数据。它最初是用于观察金星和月亮的表面

Graham was the first to introduce Synthetic Aperture Radar (SAR) for topographic mapping in 197 4. There are two kinds of information which are required for the production of topographic maps. Firstly, the various objects and features to be mapped must be presented in an image with suffici ent resolution to be identified. Secondly, a three_dimensional measurement of position, with res pect to the platform, of a sufficient number of points must be made to define the terrain surface . The three_dimensional measurement can be made by SAR interferometry with a side_looking ge ometry from both airborne and spaceborne SAR sensors.

格雷厄姆是第一个介绍合成孔径雷达(SAR)在1974年地形映射。有两种类型的信息所需的地形图的生产。首先,各种对象和特征映射必须以足够的分辨率的图像。其次,一个三维位置测量,对平台,足够数量的点必须定义地形表面。三维测量可以通过侧视SAR干涉测量几何机载和星载SAR传感器。

A Synthetic Aperture Radar is an active sensor transmitting and receiving microwave signals, i .e . Measuring distances between the sensor and the point on the Earth’s surface, where the signal is backscattered. The sensor emits electromagnetic radiation (EMR) and then records the strength and time delay of the returning signal to produce images of the ground. The EMR involved can be imagined as a sine wave. Conventional SAR images are made up (as a raster) of the amplitude or ‘strength’of the sine wave — shown in images as grey level intensity values .When the sine wave s tarts to repeat itself (phase angle > 360 degrees) , one cycle of phase has occurred . If we collect t wo separate images from exactly the same satellite position (same range) , but at different times with nothing in the target area changing, one would expect the two sine waves from each image t o be the same and in phase with each other . 合成孔径雷达是一个活跃的传感器传送和接收微波信号,我即。测量传感器之间的距离和地球表面上的点,背散射信号。传感器发出的电磁辐射(EMR),然后记录返回信号的强度和时间延迟产生的地面图像。涉及的EMR可以想象为一个正弦波。传统的SAR图像是由(光栅)的振幅或强度相近正弦波-所示图像灰度级强度值当正弦波开始重演(相位角> 360度),一个周期的阶段发生。如果我们收集两个单独的图片完全相同的卫星位置相同(范围),但在不同的时间与目标区域中没有改变,人会期望每个图像的两个正弦波是相同的,彼此在阶段。

In practice, the position of the satellite between two image acquisitions is never identical, and th e corresponding difference in the path (distance between satellite and ground) means there is a d ifference in phase between the two signals — a phase shift. The physical path difference can be e xpressed as an integer number of wavelengths plus the fraction of one wavelength. It can also be expressed as a difference in phase angle between the two signals. SAR interferometry makes use of this phase information by subtracting the phase value in one image from that of the other, for the same point on the ground. This is, in effect, generating the interference between the two pha ses signals and is the basis of interferometry .For the interferometric process to work successfully, a degree of similarity, or correlation must exist in the surface properties between the two image acquisitions . In most parts of the world, particularly temperate regions, correlation between i mages will degrade with time due to changing / moving vegetation, differing climatic condition