gprMax用户指南：3D电磁波模拟软件

GprMAX

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"gprmax说明书.pdf" gprMax是一款用于模拟地面穿透雷达（Ground-Penetrating Radar, GPR）的开源、有限差分时域（Finite-Difference Time-Domain, FDTD）软件。该软件结合了深度学习技术，使得用户能够对地下结构进行精确的仿真和分析。 1. **什么是gprMax?** gprMax是一款专门设计用于模拟GPR信号传播的软件工具。它基于FDTD方法，能够模拟电磁波在各种介质中的传播，包括地表下的土壤、岩石和其他结构。这种工具在地质调查、考古研究、基础设施检测等领域有着广泛的应用。 2. **包概述** gprMax包含了一系列模块和功能，能够处理GPR模型的创建、求解和后处理。用户可以定义不同的材料属性、构建复杂的几何形状，并设置源信号和接收器参数。 3. **安装与运行** 安装过程简单，用户可以通过阅读指南按照步骤操作。运行gprMax需要配置相应的环境，如确保系统满足硬件需求并安装必要的依赖库。软件提供命令行界面，用户可以输入参数启动模拟。 4. **软件特性** - **新功能与变化**：每个新版本可能都会引入新的特性和改进，用户可以在更新日志中找到这些信息。 - **关键功能**：支持吸收边界条件、体素化空间离散化、正交坐标系、平面波源、以及各种数据输出格式。 5. **GPR建模指导** - **基本概念**：涵盖电磁波传播的基础理论，包括波的反射、折射和衰减。 - **坐标系统与约定**：软件采用特定的坐标系统来表示模型，用户需要了解这些规则来正确设置模型。 - **空间离散化**：通过体素化将连续空间转化为离散网格，用于FDTD计算。 - **吸收边界条件**：为了防止波的反射，软件采用吸收边界条件来模拟无限大介质。 6. **输入文件命令** 输入文件是gprMax的核心，包含了模型的所有参数。它包括： - **基本命令**：定义模型的基本设置，如网格大小、时间步长等。 - **通用命令**：控制模拟的一般选项，如输出频率范围。 - **材料命令**：指定各区域的电磁性质。 - **对象构造命令**：定义模型的几何形状和位置。 - **源和输出命令**：设置发射器和接收器，以及选择要记录的数据。 - **PML命令**：配置Perfectly Matched Layers（PML），用以模拟边界吸收。 7. **输出数据** 输出数据包括电磁场的分布、几何形状信息以及A扫描、B扫描等可视化结果。 8. **绘图** gprMax提供内置的绘图功能，可以生成A扫描（时间-幅度图）、B扫描（水平切片图）和天线参数图，以及预设和自定义的波形。 9. **文件工具** 提供了脚本和转换工具，如将旧版本输入文件转换为新版本格式，合并输出文件，以及将图像数据转换为HDF5格式。 10. **脚本输入文件** 用户可以编写Python脚本来自动化输入文件的创建，包括定义常量、变量以及输入命令函数。 11. **并行计算支持** gprMax支持OpenMP和MPI进行多核并行计算，还能够适应高性能计算（HPC）环境，提高模拟效率。 gprMax通过其强大的功能和灵活性，为GPR领域的研究人员和工程师提供了有力的工具，使他们能够深入理解和预测地下结构的行为。通过深入学习集成，gprMax能够进一步优化模型参数，提升预测准确性。

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gprMax User Guide, Release 3.1.5

• #add_dispersion_drude is used to add Drude dispersive properties to a #material

• #soil_peplinski is a soil mixing model that can be used with #fractal_box to generate soil(s)

with more realistic dielectric and geometric properties

• #cylindrical_sector is a new object building command

• #geometry_view replaces #geometry_file or #geometry_vtk and is used to create views of the

geometry of the model in open source Visualization Toolkit (VTK) (http://www.vtk.org) format which can

be viewed in many free readers, such as Paraview (http://www.paraview.org)

• #fractal_box is used to create a volume with a fractal distribution of properties

• #add_surface_roughness is used to add a rough surface to a #fractal_box

• #add_surface_water is used to add surface water to a #fractal_box that has a rough surface

• #add_grass is used to add grass to a #fractal_box

• #waveform is used to specify a waveform shape, and works in conjunction with the changed source

commands

• #magnetic_dipole is used to introduce a magnetic dipole source, i.e. current on a small loop

• #pml_cfs is an advanced command for adjusting the CFS parameters used in the new PML

2.1.2 Changed commands

• All object building commands support anisotropy via additional material identiﬁers, e.g. #box: 0.0

0.0 0.0 0.1 0.1 0.1 matX matY matZ

• Dielectric smoothing can be turned on (the default setting) or off for any volumetric object building com-

mand by specifying a character y (on) or n (off) after the material identiﬁer, e.g. #sphere: 0.5 0.5

0.5 0.25 sand n

• #triangle can now create both triangular patches (2D) and triangular prisms (3D) via a thickness pa-

rameter

• #pml_cells replaces #pml_layers and can now be used to control the number of cells of PML on the

six faces of the model domain. The number of cells can be set to zero on any of the faces to turn that PML

off if desired. The default behaviour (if this command is not speciﬁed) is to use 10 cells.

• #hertzian_dipole and #voltage_source now specify polarisation, location, any additional pa-

rameters, and an identiﬁer to link to a #waveform command

• #snapshot no longer requires a type, as only VTK snapshot ﬁles are now produced

• #num_of_procs is now called #num_threads

• #tx_steps is now called #src_steps

2.1.3 Retired commands

• #analysis and #end_analysis are no longer required as: sources and receivers can be speciﬁed

anywhere is the input ﬁle; the output ﬁle automatically has the same name as the input ﬁle with a .out

extension; the format of the output ﬁle is now HDF5 (http://www.hdfgroup.org/HDF5/); gprMax can be run

with the syntax gprMax my_input_file -n number_of_runs, where number_of_runs can

be used to rerun the model for creating scans and/or moving geometry between runs.

• #tx is no longer required as the polarisation and position of a source is now speciﬁed in the source com-

mand, e.g. #hertzian_dipole: y 0.05 0.05 0.05 myPulse

• #cylinder_new has become #cylinder

• #cylindrical_segment was under-used and its effect can be created by cutting a #cylinder with

a #box

10 Chapter 2. Software Features

gprMax User Guide, Release 3.1.5

• #bowtie can be created using the new behaviour of #triangle

• #number_of_media is not required with the new Python code

• #nips_number is not required with the new Python code

• #media_file was under-used

• #geometry_file has been replaced with the #geometry_view command

• #medium has been replaced with the #material command

• #abc_type, #abc_order, #abc_stability_factors, #abc_optimization_angles, and

#abc_mixing_parameters are not required as the Higdon ABCs have been removed

• #huygens_surface will become part of the new #plane_wave command which is yet to be imple-

mented

2.1.4 Commands yet to be implemented

There are commands from previous versions of gprMax that are planned for this version, but are yet to be imple-

mented. These will be introduced in a future update. They are #thin_wire and #plane_wave.

2.1.5 Migrating old input ﬁles

gprMax includes a Python module (in the tools package) to help you migrate old input ﬁles, written for pre-

vious versions of gprMax, to the syntax of the new commands. The module will do its best to convert the

old ﬁle and write a new one, however, you should still carefully check the new ﬁle to make sure it is what

you intended! Usage (from the top-level gprMax directory) is: python -m tools.inputfile_old2new

my_old_inputfile.in.

2.2 Key features

2.2.1 Python scriptable input ﬁles

The input ﬁle has now been made scriptable by permitting blocks of Python code to be speciﬁed between

#python and #end_python commands. The code is executed when the input ﬁle is read by gprMax. You

don’t need any external tools, such as MATLAB, to generate larger, more complex input ﬁles for building intricate

models. Python scripting means that gprMax now includes libraries of more complex objects, such as antennas,

that can be easily inserted into a model. You can also access a number of built-in constants from your Python

code. For further details see the Python section.

2.2.2 Dispersive materials

gprMax has always included the ability to represent dispersive materials using a single-pole Debye model. Many

materials can be adequately represented using this approach for the typical frequency ranges associated with GPR.

However, multi-pole Debye, Drude and Lorentz functions are often used to simulate the electric susceptibility of

materials such as: water [PIE2009], human tissue [IRE2013], cold plasma [LI2013], gold [VIA2005], and soils

[BER1998], [GIAK2012], [TEI1998]. Electric susceptibility relates the polarization density to the electric ﬁeld,

and includes both the real and imaginary parts of the complex electric permittivity variation. In the new version of

gprMax a recursive convolution based method is used to express dispersive properties as apparent current density

sources [GIA2014]. A major advantage of this implementation is that it creates an inclusive susceptibility function

that holds, as special cases, Debye, Drude and Lorentz materials. For further details see the material commands

section.

2.2. Key features 11

gprMax User Guide, Release 3.1.5

2.2.3 Realistic soils, heterogeneous objects and rough surfaces

The inclusion of improved models of soils is important for many GPR simulations. gprMax can now be used to

create soils with more realistic dielectric and geometrical properties. A semi-empirical model, initially suggested

by [DOB1985], is used to describe the dielectric properties of the soil. The model relates relative permittivity of

the soil to bulk density, sand particle density, sand fraction, clay fraction and water volumetric fraction. Using this

approach, a more realistic soil with a stochastic distribution of the aforementioned parameters can be modelled.

The real and imaginary parts of this semi-empirical model can be approximated using a multi-pole Debye function

plus a conductive term. This can now be achieved in gprMax using the new dispersive material functionality. For

further details see the material commands section.

Fractals are scale invariant functions which can express the topography of the earth for a wide range of scales

with sufﬁcient detail [TUR1987]. For this reason fractals have been chosen to represent the topography of soils.

Fractals can be generated by the convolution of Gaussian noise with an inverse Fourier transform of

𝑘𝑏

, where

𝑘 is the wavenumber and 𝑏 is a constant related to the fractal dimension [TUR1997]. gprMax can now generate

heterogeneous volumes (boxes) with realistic soil properties that can have rough surfaces applied. For further

details see the fractal object building commands section.

Fractal correlated noise [TUR1997] is used to describe the stochastic distribution of the properties of soils. This

approach has been chosen because it has been shown that soil-related environmental properties frequently obey

fractal laws [BUR1981], [HILL1998]. For further details see the material commands section and the fractal object

building commands section.

2.2.4 Library of antenna models

gprMax now includes Python modules with pre-deﬁned models of antennas that behave similarly to commercial

antennas [WAR2011] [STA2017]. Currently models of antennas similar to Geophysical Survey Systems, Inc.

(GSSI) (http://www.geophysical.com) 1.5 GHz (Model 5100) antenna, and 400 MHz antenna, as well as MALA

Geoscience (http://www.malags.com/) 1.2 GHz antenna are included. By taking advantage of Python scripting in

input ﬁles, using such complex structures in a model is straightforward without having to be built step-by-step by

the user. For further details see the Python section.

2.2.5 Anisotropic materials

It is possible to specify objects that have diagonal anisotropy which allows materials such as wood and ﬁbre-

reinforced composites, often imaged with GPR, to be more accurately modelled. Standard isotropic objects specify

one material identiﬁer that deﬁnes the same properties in x, y, and z directions. However, every volumetric object

building command can also be speciﬁed with three material identiﬁers, which allows properties for the x, y, and z

directions to be separately deﬁned.

2.2.6 Dielectric smoothing

At the boundaries between different materials in a model there is the question of what electric and magnetic

material properties to use?

• Should the last object to be deﬁned at that location dictate the electric and magnetic properties?

• Should an average set of electric and magnetic properties of the materials of the objects that share that

location be used?

This latter option is often referred to as dielectric smoothing and has been shown to result in more accurate

simulations [LUE1994] [BOU1996] [WHI2009]. To address this question gprMax includes an option to turn

dielectric smoothing on or off for volumetric object building commands. The default behaviour (if no option is

speciﬁed) is for dielectric smoothing to be on. The option can be speciﬁed with a single character y (on) or n (off)

given after the material identiﬁer in each object command. When dielectric smoothing is on gprMax calculates

the arithmetic mean of the electric and magnetic properties of the surrounding Yee cells, to use for the single Yee

cell edge (boundary) of interest.

12 Chapter 2. Software Features

gprMax User Guide, Release 3.1.5

2.2.7 Perfectly Matched Layer (PML) boundary conditions

With increased research into quantitative information from GPR, it has become necessary for models to be able to

have more efﬁcient and better-performing Perfectly Matched Layer (PML) absorbing boundary conditions. Since

2005 gprMax has featured PML absorbing boundary conditions based on the uniaxial PML (UPML) [GED1998]

formulation. A PML based on a recursive integration approach to the complex frequency shifted (CFS) PML

[GIA2012] has been adopted in the new version of gprMax. A general formulation of this RIPML, which can be

used to develop any order of PML, has been used to implement ﬁrst and second order CFS stretching functions.

One of the attractions of the RIPML is that it is easily applied as a correction to the ﬁeld quantities after the

complete FDTD grid has been updated using the standard FDTD update equations. gprMax now offers the ability

(for advanced users) to customise the parameters of the PML which allows its performance to be better optimised

for speciﬁc applications. Additionally, since the RIPML is media agnostic it can be used without change to

problems involving dispersive and anisotropic materials. For further details see the PML commands section.

2.2.8 Open source, robust, ﬁle formats

Alongside improvements to the input ﬁle there is a new output ﬁle format – HDF5

(http://www.hdfgroup.org/HDF5/) – to manage the larger and more complex data sets that are being gener-

ated. HDF5 is a robust, portable and extensible format with a number of free readers available. For further details

see the output ﬁle section.

In addition, the Visualization Toolkit (VTK) (http://www.vtk.org) is being used for improved handling and view-

ing of the detailed 3D FDTD geometry meshes. The VTK is an open-source system for 3D computer graph-

ics, image processing and visualisation. It also has a number of free readers available including Paraview

(http://www.paraview.org). For further details see the geometry view command.

2.2. Key features 13

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