IEEE Geoscience and Remote Sensing Magazine - December 2022 - 85

0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 0.2 0.3 0.4 0.5 0.6
Scanning Positions (m)
(a)
×10-8
0.2
0.4
0.6
-0.4
-0.2
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 0.2 0.3 0.4 0.5 0.6
Scanning Positions (m)
(b)
×10-8
0.2
0.4
0.6
-0.2
-0.4
-0.6
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 0.2 0.3 0.4 0.5 0.6
Scanning Positions (m)
(c)
FIGURE 20. Migration using different trial velocities at (a) 5% less than true velocity, (b) true velocity, and (c) 5% more than true velocity.
functions have good agreement with the corresponding
measured Green's functions (Figure 19). The parameters
of these media are extracted by minimizing the objective
functions through gradient-based optimization. To fix
the beginning point, initial information about the model
parameters is required. The inversion process is nonlinear
and ill posed when the objective function has multiple
minima. To overcome this problem, a global optimization
scheme is necessary. FWI schemes are accurate, but
the inversion process is highly nonlinear and time-consuming
and thus unsuitable for real-time application. A
comparison of different velocity estimation approaches is
presented in Table 4.
The subsurface medium velocity has a significant
impact on the focusing accomplished through time reversal.
The focusing is confined to the exact location of
the buried scatterer if TRI is performed with proper velocity;
otherwise, it diverges from the true location. The
amount of focusing can be quantified in terms of the
PSNR for each trial velocity, and the optimum velocity
is obtained where the PSNR is maximum. The impact
of estimation accuracy on GPR imaging is demonstrated
though Kirchhoff migration. It is observed that velocities
lower than the true velocity result in insufficient
migration, whereas higher-than-true velocity results in
excessive migration (Figure 20).
CONCLUSION
The primary goal of this work was to provide an overview
of the importance of velocity estimation as well
as the various estimation approaches that are available,
their applicability, the pros and cons of each method,
and the impact of estimation accuracy on imaging. In
this article, we reviewed different subsurface velocity
estimation procedures and validated some of the techniques
available in literature. It is analyzed from the survey
that many popular velocity estimation techniques
are not suitable in some particular field conditions. Despite
the fact that many velocity estimation approaches
DECEMBER 2022 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE
have been proposed in the literature, most of them are
suitable for either homogeneous media or multilayer media
with each layer being homogeneous. In some cases,
the techniques may fail to estimate the media properties
without some prior information about the media. Open
issues are still there while dealing with various challenging
realistic scenarios, such as nonhomogeneous media,
which require further investigations.
ACKNOWLEDGMENT
This research work is supported and sponsored by the Impacting
Research Innovation and Technology-Science and
Engineering Research Board project for the development of
GPR for the detection of subsurface objects.
AUTHOR INFORMATION
Swarna Laxmi Panda (517ec1013@nitrkl.ac.in) is with the
Department of Electronics and Communication Engineering,
National Institute of Technology Rourkela, Rourkela
769008 India.
Subrata Maiti (smaiti@nitrkl.ac.in) is with the Department
of Electronics and Communication Engineering, National
Institute of Technology Rourkela, Rourkela 769008,
India. He is a Member of IEEE.
Upendra Kumar Sahoo (sahooupen@nitrkl.ac.in) is with
the Department of Electronics and Communication Engineering,
National Institute of Technology Rourkela, Rourkela
769008, India. He is a Member of IEEE.
REFERENCES
[1] M. Metwaly, " Application of GPR technique for subsurface
utility mapping: A case study from urban area of Holy Mecca,
Saudi Arabia, " Measurement, vol. 60, pp. 139-145, Jan. 2015.
[Online]. Available: https://www.sciencedirect.com/science/
article/pii/S0263224114004448, doi: 10.1016/j.measurement.
2014.09.064.
[2]
L. B. Ciampoli, A. Benedetto, L. Pajewski, A. M. Alani, and F.
Tosti, " A comparison between different central frequencies of
investigation in buried utility detection through GPR: A study
85
×10-8
0.2
0.4
0.6
-0.2
-0.4
-0.6
Time (s)
Time (s)
Time (s)

https://www.sciencedirect.com/science/article/abs/pii/S0263224114004448 https://www.sciencedirect.com/science/article/abs/pii/S0263224114004448

IEEE Geoscience and Remote Sensing Magazine - December 2022

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - December 2022