IEEE Geoscience and Remote Sensing Magazine - December 2021 - 186

a helmet-mounted display to assist in deciding whether the
landing zone is safe.
The principle of the helicopter-mounted FL SAR system
THIS EMERGING
TECHNOLOGY HAS GAINED
AN INCREASING INTEREST
DUE TO ITS HUMANITARIAN
AND MILITARY
APPLICATIONS WHILE
MAINTAINING OPERATOR
SAFETY.
for 3D landing zone mapping is explained in Figure 15.
The system is equipped with a 2-m-wide front-bumpertype
linear antenna array,
which provides resolution in
the azimuth direction, while
the forward motion of the
platform at constant height
creates a synthetic aperture
with sufficient elevat ion
look-angle diversity to offer
resolution in the vertical direction.
The radar waveform
bandwidth (between 0.5 and
1 GHz) provides resolution
in the down-range direction.
To date, several studies based
on computer simulations have demonstrated the feasibility
of this concept and emphasized some of the major challenges
associated with it.
CONCLUSIONS
In this article, we presented an overview of image formation
and subsurface target-detection techniques using FLGPR.
This emerging technology has gained an increasing
interest due to its humanitarian and military applications
while maintaining operator safety. We provided a balanced
account of existing methods and discussed their respective
advantages and limitations. The presented image formation
approaches included conventional back-projection,
microwave tomographic techniques, and CS-based methods,
with the last of these assuming the underlying scene
to be sparse. We also outlined different approaches to deal
with clutter arising from the rough ground interface. Finally,
we detailed statistical and spectral techniques for landmine
detection in FL-GPR applications.
While a broad range of imaging, target-detection, and
clutter-suppression techniques have been proposed in the
literature, there are still open issues, particularly associated
with the detection of plastic targets and real-time operation
under various challenging realistic conditions, that require
further investigations. New machine learning algorithms
could also be devised for target classification, especially in
the presence of strong clutter.
The future trend of radar deployment on unmanned
platforms (both aerial and ground based) brings forth
new challenges. From an implementation perspective,
the antenna design is a critical issue, especially when using
antenna arrays with the limited space available on an
unmanned aerial platform. At the preferred operational
frequency range of 0.3-3 GHz, depending on the radiation
performance, the antennas can be quite bulky and heavy.
Compact designs using metamaterial-based UWB conformal
antenna technology are a promising potential solution
to the implementation challenges.
From an algorithmic perspective, multiplatform data
fusion strategies under both communication and computation
constraints could be devised to achieve enhanced performance
using a distributed network of unmanned platforms.
In short, research into devising effective solutions
for addressing the aforementioned challenges is critical to
providing performance guarantees.
2D Synthetic
Array
1D Linear
Array
(a)
Forward Motion
Equivalent
2D Array
∆φ
∆θ
Obstacle
(b)
FIGURE 15. (a) A schematic representation of the helicopter-borne
FL SAR system for 3D landing-zone imaging, showing the proposed
configuration involving a linear antenna array. (b) The equivalence
of this imaging system with a 2D antenna array.
186
AUTHOR INFORMATION
Davide Comite (davide.comite@uniromal.it) received his
master's degree (cum laude) in communications engineering
and Ph.D. degree in electromagnetics and mathematical
models for engineering from the Sapienza University
of Rome, Rome, Italy, in 2011 and 2015, respectively. He
was a visiting Ph.D. student with the Institute of Electronics
and Telecommunications of Rennes, University of Rennes
1, Rennes, France, from March to June 2014 and a postdoctoral
researcher with the Center of Advanced Communications,
Villanova University, Villanova, Pennsylvania, USA,
in 2015. He is currently a post-doctoral researcher with the
Sapienza University of Rome, Rome, 00184, Italy. His research
interests include the study of scattering from natural
surfaces as well as GNSS reflectometry over the land, microwave
imaging and object detection performed through
ground-penetrating radar, modeling of the radar signature
in forward-scatter radar systems, study and design of leakywave
antennas, and generation of nondiffracting waves and
pulses. He has been a recipient of a number of awards at
national and international conferences. Most recently, he
received a Young Scientist Award for the General Assembly
and Scientific Symposium of the International Union
IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE DECEMBER 2021
Linear Array
IEEE Geoscience and Remote Sensing Magazine - December 2021

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