1.1SAR原理

https://pan.quark.cn/s/505995669f03?pwd=255

InSAR原理

内容贡献者包括：Scott Hensley， Anthony Freeman， Jakob van Zyl， Piyush Agram， Howard Zebker

本笔记本介绍了合成孔径雷达干涉测量的基础知识。

什么是雷达？
基本定义
什么是合成孔径雷达？
雷达图像的属性
什么是合成孔径雷达干涉测量？
SAR的其他重要模式有哪些？
什么是距离-多普勒几何，为什么它很重要，以及它与地理坐标的关系？

第一部分：雷达成像基础

引言

你阅读这篇文章是因为你对合成孔径雷达（SAR）的大地测量方面感兴趣，特别是干涉合成孔径雷达（InSAR）。从技术角度来看，SAR和InSAR相当复杂，即使对该领域的专家来说，一个能够照亮地面上巨大足迹的仪器如何能够提供几乎任意精细分辨率的图像，以及图像点随时间的相对运动达到毫米到厘米级的精度，也可能是一个奇迹。这可以通过首先查看处理前的原始数据“图像”来说明。

本笔记本中任何计算示例所使用的雷达和航天器参数及常数表

import numpy as np Lambda = 0.24 L_a = 10. W_a = 2. theta_l = 30. * np.pi/180. theta_sq = 0. * np.pi/180. v_sc = 7500. h_sc = 750000. B_r = 20.e6 tau_r = 10.e-6 f_p = 1600. P_T = 4000. T_r = 300. L_cr =2.4 c = 299792456 k = 1.38064852e-23 G = 6.672e-11 M_E = 5.9742e24

利用距离向编码实现更好的分辨率

如果无法发射足够窄且功率足以达到预期结果的脉冲，通常的做法是在脉冲中发射编码波形，为脉冲信号创建更宽的带宽。分辨率则是带宽的倒数。具体来说，对于一个脉冲持续时间为且没有编码波形的雷达脉冲，其分辨率为

而对于一个波形编码后带宽为的雷达脉冲，其分辨率为

rho = h_sc / np.cos(theta_l) Delta_rho_taur = c * tau_r / 2. Delta_rho_Br = c * (1./B_r) / 2. print("Spacecraft altitude =",f"{h_sc:.2f}","m") print("Pulse length =",f"{1.e6*tau_r:.2f}","microsec") print("Pulse Bandwidth=",f"{1.e-6*B_r:.2f}","MegaHertz") print("Range from spacecraft to boresight intersection with ground =",f"{rho:.2f}","m") print("Range resolution based on pulse duration = \"",f"{Delta_rho_taur:.2f}","m") print("Range resolution based on bandwidth of coded range pulse = \"",f"{Delta_rho_Br:.2f}","m")

地面分辨率变化

tau_p = 0. theta=np.linspace(25.,45.,100) Delta_rhog_Br = Delta_rho_Br / np.sin((theta-tau_p) * np.pi / 180.) tau_p = 10. Delta_rhog_Br_10deg = Delta_rho_Br / np.sin((theta-tau_p) * np.pi / 180.) tau_p = 20. Delta_rhog_Br_20deg = Delta_rho_Br / np.sin((theta-tau_p) * np.pi / 180.) plt.style.use('seaborn-v0_8-whitegrid') fig = plt.figure() ax = plt.axes() plt.plot(theta,Delta_rhog_Br,label='0$^\\circ$ slope') plt.plot(theta,Delta_rhog_Br_10deg,label='10$^\\circ$ slope') plt.plot(theta,Delta_rhog_Br_20deg,label='20$^\\circ$ slope') plt.xlabel("Look angle $(^\\circ)$") plt.ylabel("Ground Range Resolution ") plt.title("Ground Range Resolution versus look angle for different slopes") plt.legend(loc='best');

一些波束尺寸示例

theta_3db_az = 0.866 * Lambda / L_a # 0.866 factor typically more representative of actual 3dB point theta_3db_el = 0.866 * Lambda / W_a Delta_X_az = rho * theta_3db_az Delta_X_el = rho * theta_3db_el / np.cos(theta_l) print("Antenna Length in azimuth (along track) =",f"{L_a:.2f}","m") print("Antenna Width in elevation (perp to boresight and azimuth)=",f"{W_a:.2f}","m") print("Azimuth beamwidth =",f"{180.*theta_3db_az/np.pi:.2f}","degrees") print("Elevation beamwidth =",f"{180.*theta_3db_el/np.pi:.2f}","degrees") print("Azimuth beam extent at reference range =",f"{Delta_X_az:.2f}","m") print("Elevation beam extent at reference range =",f"{Delta_X_el:.2f}","m")

方位向分辨率示例

信号从航天器到地面再返回的双程传播，使得方位向波束内的多普勒带宽展宽比人们预期的要大一倍。因此，合成孔径长度可以被认为是照亮刈幅范围的两倍。

# allow for some playing with parameters locally. theta_3db_az = 0.866 * Lambda / L_a # 0.866 factor typically more representative of actual 3dB point Delta_X_az = rho * theta_3db_az SynAp_az = 2. * Delta_X_az theta_SynAp = 0.866 * Lambda / SynAp_az delta_x_SynAp = rho * theta_SynAp print("Azimuth antenna length =",f"{L_a:.2f}","m") print("Azimuth beam extent at reference range illuminating a target =",f"{Delta_X_az:.2f}","m") print("Synthetic aperture length (effective) =",f"{SynAp_az:.2f}","m") print("Synthetic aperture effective beamwidth =",f"{1000.*180.*theta_SynAp/np.pi:.3f}","millidegrees") print("Synthetic aperture resolution =",f"{delta_x_SynAp:.3f}","m")

对于一个距离向带宽为40 MHz，天线尺寸在高度向上为2米，飞行方向上为12米的条带模式SAR图像，其固有分辨率是多少？

A. 距离向12米，飞行方向12米

B. 距离向1米，飞行方向6米

C. 距离向3米，飞行方向1米

D. 距离向3米，飞行方向6米