IDL-based SAR image processing and quality evaluation system
It mainly introduces the basic components and characteristics of scientific computing visualization IDL, and applies IDL's human-computer interaction, signal processing, visualization and open interface and other powerful functions to SAR image processing and quality evaluation systems.Through the graphical user interface, users only need With simple system operation, detailed and intuitive processing and evaluation results can be obtained.
Keywords: IDL (InteracTIve Data Language) software engineering synthetic aperture radar image processing
Scientific computing visualization is an emerging edge technology proposed and developed by American scientists in the late 1980s. It converts the data generated during the scientific calculation process and the calculation results into graphical or image information, and can be interactively analyzed to become The powerful tool for human analysis and control of information in the era of information explosion. The IDL (InteracTIve Data Language) fourth-generation scientific computing visualization language developed by RSI of the United States has the characteristics of openness, high-dimensional analysis capabilities, scientific computing capabilities, practicality and visual analysis. It integrates all scientific computing environments. The necessary tools enable users to visually analyze any scientific data. Many users not only use IDL for subject research, but also form a batch of commercial application software, such as remote sensing professional image analysis software ENVI, synthetic aperture radar (SAR) data terrain correction commercial software 3-D SAR Ground StaTIon and so on. This article mainly introduces the structural characteristics based on IDL and the developed SAR image processing and quality evaluation system. The system uses IDL's powerful functions such as human-computer interaction, signal processing, visualization and open interface to integrate most of the functions and operations required for SAR image processing and quality assessment.
1 Composition and characteristics of IDL
IDL consists of the following basic software packages:
1.1 Signal processing and image processing
As a widely used technology, signal processing occupies a very important position in modern data processing. IDL has developed a very complete signal processing software package, which not only includes a large number of frequency domain signal analysis methods (such as: 1-7 dimensional FFT, frequency domain filtering and analysis, multiple high-dimensional convolution, spectrum analysis, complex space pole analysis There are also a large number of spatial domain analysis and processing methods (such as: morphological analysis, spatial filtering, edge extraction, waveform analysis, spatial transformation, etc.) and time domain analysis (such as: time series analysis, wavelet transform and analysis (152 functions) , Signal editing, etc.). As a special signal processing, image processing has also become the main function of this software package. In addition to the general signal processing methods, it also has color space transformation, true color-false color transformation, histogram statistics and analysis, magnification and translation. A variety of unique functions for image processing such as geographic analysis and polynomial distortion. This software package provides users with a powerful signal and image analysis tool.
1.2 Visualization software package
IDL visualization consists of two parts.One is two-dimensional visualization.It includes a variety of surface generation methods, surface fitting methods, surface smoothing methods, weighted surface generation methods, one-dimensional and two-dimensional data display, multi-data overlay, vector Data display, etc. Another very important part is the visualization of 3D and high-dimensional data. Its main functions are 3D display, 3D animation (using OpenGL), 3D solid analysis and visualization, 4D data display and analysis, real-time regular and irregular grid generation, Z-buffered graphics and entity equivalent analysis and display, etc.
1.3 Mathematical analysis software package
Mathematical analysis is the foundation of scientific computing visualization, so IDL has extremely strong data analysis capabilities. It includes: integration (over ten integration methods), feature vector space analysis system, linear system, spare linear system, nonlinear system, multiple evaluation methods, multidimensional optimization system, correlation analysis and regression prediction system, model analysis and detection System, high-dimensional inspection value, etc.
1.4 Map projection and conversion software package
IDL's emphasis on geography is reflected in its unique map projection software package, which not only contains almost all map projection formulas and models, but also can be fully visualized (displayed in graphics and high-resolution images), it can be Any image data can be corrected by map projection and converted between projections, so that users of earth science can easily realize their own functions.
1.5 Graphic interface tool package
As a visual language, the power of the user graphical interface (GUI) directly determines the quality of its application. IDL provides a powerful GUI (Graphical User Interfaces), which includes dozens of user tools, such as 3D flight tools, animation tools, registration tools, Bitmap editing tools, color table editing and application, interface and menu generation tools, Entity analysis tools, etc.
1.6 Development and editing tools
In order to make it easier for users to use for software development, IDL not only establishes a visual programming environment IDE for users, but also provides users with a large number of programming tools.
1.7 ODBC database interface
IDL has developed a universal ODBC interface that allows users to not only visually analyze data but also manage all data, which is an inevitable trend in the development of visualization software.
In addition, starting from IDL5.0, IDL changed the old programming structure, adopted object-oriented programming methods, and provided a new object-oriented graphic model structure, so that users can use any graphics device without regenerating graphics. Perform various operations on the graphics model target (such as calculation, display, printing, etc.); IDL uses OpenGL technology, which greatly enhances its visual ability of 3D animation, making 3D animation and analysis closely combined, it can also use OpenGL Hardware acceleration environment, so that the three-dimensional graphics display can reach the hardware display trend; IDL open interface uses different technologies to communicate with operating systems and programs in other languages.For example, IDL's Spawn method can generate a subprocess for IDL and operating system. To communicate with each other, the Call-external method can call C or Fortran subroutines in the dynamic link library (DLL) in IDL.
2 IDL-based SAR image processing and quality evaluation system
As a very mature visualization language, IDL has been widely used in medicine, geoscience, astronomy, astrophysics, aerospace science, applied science, military, environmental science, material science and other disciplines, and its users are located in more than 50 countries and regions in the world. . Its largest users include NASA, the National Jet Laboratory, the United States National Land Administration, the National Oceanic Administration, the European Space Agency, major observatories in the world, medical schools in the United States and Europe.
Our research group has long been engaged in research on imaging processing of spaceborne synthetic aperture radar (SAR), and recently developed an IDL-based SAR image processing and quality evaluation system. The operating system used is Windows 98, and the application software is IDL5.0 launched by the American RSI company in March 1998. Its visualization functions, graphics processing capabilities, and user development environment have become the main reasons for choosing it.
Since this system will involve a large number of image display and processing operations, including the operation of three-dimensional images, the hardware's graphics processing capabilities will play a vital role in the performance of the system. However, because of the use of IDL5.0 for programming, its powerful graphics processing function can complete the image display and processing on the ordinary microcomputer, and considering the configuration of the user's hardware, the ordinary microcomputer is selected for software development and operation.
The whole system organized by modular design idea consists of four modules, namely: user interface, preprocessing module, main processing module and speckle suppression algorithm library. The system block diagram is shown in Figure 1.
Among them, the human-computer interaction dialogue of the entire system is written using various Widgets in IDL5.0. When the user performs a certain operation on a component, IDL will correspond to the corresponding event and call the IDL child in the event response. program. The system processing and the display of evaluation results make full use of IDL's histogram statistics, 3D graph display, and contour display. Taking the speckle suppression algorithm library as an independent module, its main purpose is to make the system have good scalability and easy to maintain. Each speckle suppression algorithm is written in C language, which can be called using the Call-external method in IDL, taking into account the characteristics of the fast speed of the C program budget. Through powerful functions such as IDL's human-computer interaction, signal processing, visualization, and open interfaces, the SAR image processing process and various operations are organized organically and organized in an orderly manner, integrating SAR images Most of the functions and operations required for processing, and interact with these functions through a visual graphical user interface, so that users can complete speckle noise suppression and image quality of SAR images with simple operations Evaluation.
In short, IDL is a computing visualization language with openness, high-dimensional analytical capabilities, scientific computing capabilities, practical and visual analysis, which can be applied to many research fields. In this paper, the powerful functions of IDL are used to implement the SAR image processing and quality evaluation system based on IDL language. Its good graphical user interface allows users to obtain detailed and intuitive processing and evaluation results by performing simple system operations.
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