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predicted that intelligent groundwater-monitoring systems
developed in the near future could integrate dc resistivity, the
induced polarization effect, and MTEM measurements into
one system as a single step, combining current excitation and
time-sharing measurement techniques. It is possible to solve
the unique inversion problem of geophysics and enhance the
efficiency of underground measurements.
Also, geophysical exploration together with the necessary
drilling confirmation was identified as an effective method
for mine water prospecting and management. Furthermore,
we recommend that an in-borehole resistivity measurement
system be developed to expand the detecting area. If the hidden water-conducting structure and water body within a 30-m
radius around the drill holes can be accurately explored, it
will break through the limitation of an underground working space and provide a possibility to increase the application
areas as well as supply enough evidence to uniquely determine the spatial location of a geoelectrical anomaly.
Finally, a 3D visualization software platform for data
processing and inversion for mine-resistivity methods
should be established under a unified standard as soon as
possible. In this way, it will meet the requirements of intelligent mines for advance-detection and monitoring systems
with online, dynamic, and real-time functions.

number of turn loops, transmit current waveform, and parameters of a coal series, determine the penetration depth of
MTEM with small multiturn loops by studying the velocity of
transient electromagnetic field diffusion in the whole space.

DEVELOPMENT TREND OF THE MINE TRANSIENT
ELECTROMAGNETIC METHOD
MTEM is currently the main method for advance detection.
However, its application and further development have
been plagued by following theoretical problems.
First, when small loops are used as the transmitter and
receiver for MTEM, whether they are single- or multi-turn
coils, the apparent resistivity values calculated by the ordinary late-time formula are several orders lower than the
intrinsic resistivity of the coal and surrounding rocks. This
phenomenon has confused the qualitative and quantitative
interpretation of MTEM data for almost 20 years. Therefore,
it is necessary to find out the reason to derive a reasonable
apparent-resistivity formula for MTEM.
In practice, it is customary to change the normal direction
of the transmitting and receiving loops to detect a specially
orientated geological anomaly, under the assumption that
the coupled field of the close-to-receiver response is much
stronger than that of the far-from-receiver response. We need
to find the theoretical evidence that can reveal the electromagnetic coupling relationship between the receiver and
detecting targets in different orientations, which will help us
understand how the geological noises of the stratigraphic distribution of the coal-bearing strata affect the measurements
as well as help us develop methods to suppress the interference from a nontarget.
Lastly, the time-depth conversion formulas currently used
in the processing of MTEM data are mostly extended from the
half-space formula: whether they are suitable for the whole
space still needs further validation. In addition, it is necessary
to study how factors, such as time delay, coil side length and

DEVELOPMENT TREND OF MINE-BASED
MAGNETIC RESONANCE SOUNDING AND
GROUND-PENETRATING RADAR
In principle, underground MRS and mine GPR have obvious
advantages, but their application in Chinese coal mines is not
very popular. So far, the theoretical and technical problems
have not fully emerged, and the practical effect of application
also needs further verification. Strengthening the intensity of
magnetic resonance signals, suppressing mine interference,
and maximizing the advance-detection distance are possible
areas for innovation in mine MRS and GPR. A common issue involves reducing the size of the antenna and arranging
more points in the limited section of the roadway for both
methods. The whole-space effect and roadway influence also
need to be studied. Concerning the relative stability of the
electrical parameters of the coal-bearing strata, the strongest
electromagnetic coupling effect could be obtained by changing the frequency of the emission field.

DEVELOPMENT TREND OF ELECTROMAGNETIC
WAVE TOMOGRAPHY
The modeling results show that the phase of radio waves
is of great significance to improve the resolution of tomographic imaging. Thus, the following tasks remain:
1) New instruments should be developed that can measure
the amplitude and phase of electromagnetic waves simultaneously on the basis of the principle of the imaginary-real component method. Accordingly, there is a
need to develop the phase tomography algorithm.
2) A multichannel radio imaging system should be created,
and full waveform surveying should be put into practice by
continuous measurement within a certain period of time.
3) The combination of the full waveform inversion method
with probability theory can reduce the dependence of
the conventional full waveform inversion method on the
initial geological models, and the evaluation method for
the inversion results can be provided by the probability
statistical index, which is recommended.

CONCLUSIONS AND RECOMMENDATIONS
Advance-detection technologies for a coal-mining face are relatively mature, whereas advance-detection technologies for
the roof or floor of the mining face and for the heading
face still need improvement. Because of their convenient
construction and relatively simple principles, electrical
prospecting methods play a very important role in advance detection for Chinese coal mines. The whole-space
effect under the influence of a roadway includes the inherent characteristics of all kinds of geophysical fields in an
underground mine, which should be considered in underground data acquisition, processing, and interpretation.
IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

SEPTEMBER 2019
IEEE Geoscience and Remote Sensing Magazine - September 2019

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