Note: Descriptions are shown in the official language in which they were submitted.
~ ~.g~5~
EARTH PROBING RADAR SYSTEM
Background of the Invention
1. Field of the Invention
__ _
The invention relates generally to radar syste~s for earth
probing and, more particularly, but not by way of limitation, i-t
relates to an improved method and apparatus for use in hazard
protection at a coal seam work face.
2 Description of the Prior Art
There have been previous attempts to use radar to explore
geologic ma-terials, but most of this work has been unsuccessful
except when used in salt or extremely dry formations. In most
previous operations the approach has been to apply radar techno--
loyy as developed by the Aerospace industry with direct applica-
tion to ground probing. The methods of recording and subsequen-t
signal processing that have been utilized in the Aerospace industry
were directed toward enhancing system signal to noise in the pre-
sence of random noise, and they produced reliable indica-tion only
at very short depths of penetration, on the order of a few feet.
These efforts are exemplified by U. S. Patent Nos. 3,806,795;
3,831,173; and ~,072,942. In a more recent development, U. S~
Patent No. 4,008,469 discloses a hybrid short pulse radar system
for earth probing, but here again the digital processing scheme
is directed toward enhancing system signal to noise in the pre-
sence of random noise. No prior art teaching for earth probing
radar is directed toward overcoming the problem of ~ource coherent
noise or interference, i.e., multiples and other reflections from
undesired objectives.
Summary of the Invention
The present lnvention contemplates a ground probing radar
method and apparatus which is effective to look in advance of
coal mining actlvity to provide visual display cf a coal seam
5~7
and particular discontinui-ties that may lie therein. The radar
method oL~erates in the Erequency range of 10 Megahertz to 5
Gigaher-tz and cmploys received signal processing, both analog
and digital, which aims to reduce problems inherent with source
coheren-t noise or interference as well as random noise. The re-
ceived electromagnetic energy is amplified, sampled and band
pass filtered with subsequent time gain amplification; there~after,
a time analog return signal may be viewed direc-tly and/or the
return sic3nal may be digitally processed to enable further signal
refinemen-t. A control microprocessor is utilized for both tape
record control and digital signal processing, and the processor
includes the capability for eompositing and/or stacking of comrnon
source poin-t data for output record and display.
Therefore, it is an object of the present invention to pro-
vide a ground probing radar for surveillance in coal mines, i~e.,
detection of discontinuities, abandoned well bores, e-tc.
It is yet another object of the present invention to provide
a eoal seam probing radar having rela-tively long effective range
while utilizing electronics that are permissible within the in-
mine standards of the industry, e.g., ~ISHA Standards.
It is still another objeet of this invention to provide a
ground probing radar apparatus having low power requirement and
suffieient range with subsequent signal processing capability for
materially reducing source eoherent interference.
It is also an objeet of the invention to provide gro~lnd
probing radar apparatus having the eapability to perform eommon
refleetion point staeking within the apparatus i~self in order to
reduee source coherent interferenceO
Finally, it is an objeet of the invention to provide a method
~0 for eontinually ascertaining the homogeneity of structure in a
coal seam in advance of coal mining machinery.
Other objects and advantages of the inven~ion will be evident
from the following detailed description when read in conjunction
with the accompanying drawings which illustrate the invention.
5srief Descrip~ion of the Drawings
FIG. 1 is a top plan view of coal seam and mine face with
a particular radar transmitter-receiver array;
FIG. 2 is a top plan view of a coal mine pillar having a
particular radar transmitter~receiver array;
10FIG. 3 is a -top plan view of a coal mine pillar having yet
another radar transmitter-receiver array;
FIG. 4 is a block diagram of ground probing radar as con-
structed in accordance with the present invention;
FIG. 5 is a block diagram of a control unit as utilized in
15the system of FIG. 4;
FIG. 6 is a block diagram of filter circuits as utilized
in the control unit of FIG. 5;
FIG. 7 is a block diagram of timing control circuits as
utilized in FIG. 5;
20FIG. ~ is a block diagram of a time gain function circuit
as utilized in FIG. 5;
FIG. 9 is a block diagram of microprocessor circuitry as
utilized in the control unit of FIG. 5;
FIG. 10 is a graph of voltage vs. -time illustrating a non-
25linear scan ramp as utilized in the invention; and
FIG. 11 is a scan ramp generator as utilized in the presen-t
invention.
Detailed Description of the Invention
In accordance with the objectives, the invention is directed
30to providing a reliable type of ground probing radar ~hich can be
i ~825~7
used to ascertain the condition and presence of anomalies in a
coal seam in advance of the mining machinery. FIGS. 1, 2 and 3
illustrate some of the most probable applications wherein such
equipment is utilizedO FIG. 1 illustrates a coal seam 10 and
mine face 12 adjacent a mine tunnel section 1~. There are pre-
sent in coal seam 10 a discontinuity 16, e.g., a clay vein or
void, and an abandoned and unrecorded well bore 18 for purposes
of illustra-tion.
In this case, radar reflection testing is illustrated where a
radar transmitter is energized at a plurality of preferably
equally--spaced transmitter positions 20, 2~, 24, 26, 28 and 30,
etc., to propagate energy into the coal seam 10 for reception at
a radar receiver installation at a position 32. There is also
illustrated the geometry oE source coherent interference by the
multiple ray paths of FIG. 1. That is, for energization of the
radar transmitter at a given source point, e.g., source point 26,
primary reflection paths as illustrated by only two ray paths 3~
and 36, would be incident on receiver position 32 from along the
entire or a good portion of discontinuity 16. In like manner, the
well bore 18 will provide its characteristic radar return as
incident along ray path 37 to receiver position 32. Also, a
direct path in coal 38 and direct path 39 in air are illustra-tedO
As will be further described below, the radar system of the pre-
sent invention functions through both improvement of signal to
~5 noise and definition over source coherent interference to de-tect
reliable receiver output signal for visual display of the vaLious
undesired positions within coal seam 10. This may utilize various
combinations of common source point positioning an~/or digital
stack processing depending upon the exigencies of the particular
operation.
5 ~ 7
FIG. 2 illustrates another coal mine application wherein a
coal pillar 40, as may contain a well bore 42, is analyzed both
as to dimension and anc~aly by radar transmission testing. ~rha-t
is, a plurality of radar transmitter source points 44, 4~, 48,
etc., are shot in equi-spaced sequerlce with reception of -the
electromagnetic energy on -the opposite rib 50 of coal pillar 40.
Generally speaking, coal pillars are rectangular and such -trans-
mission testing can disclose any undesired anomalies within the
pillar 40 as well as pro~iding a readout of the coal pillar dimen-
sions by analysis of the energy travel times through the coal.
Equi-spaced receiver positions are indicated at 52a, 52b through
52n. In the case of transmission testing, the source coherent
noise can be identified as the direct ray paths versus the pro-
pagation paths reflecting from side ribs 54 or 56 as well as the
other anomalies such as well bore 42. The propagation paths from
source 44 to receiver point 52c show the multiple paths as a
direct path 58, multiple side rib reflection paths as illustrated
by path 60, and a well bore reflection path ~2. Similar multiples
would occur for each source point-receiver point combination.
Yet another mode of operation is illustrated in FIG. 3 where-
in radar energy is transmitted from a plurality of equi-spaced
transmitter points 64a, 64b, . . . 64n as received at one or more
of a plurality of like receiver points. Thus, a coal pillar 70,
including a well bore 72, may be examined for dimension and
anomalies by means of sequentially positioned radar transmitter
74 and radar receiver 76. In the reception mode, the source
coherent interference is further complicated by the presence of
not only multi-wall interface reflection as shown by reflection
paths 78, but single-wall reflection paths 80, direct propagation
path 82 in coal, and the propagation path of the tran~mitted
I ~25~
energy in air as shown by arrow 8~ along the front rib 86 of
pillar 70. However, here again the source coherent interference
can be eliminated or sufficiently reduced by processing in accor-
dance with the present method so that reliable data indicating
targets within the coal seam are detectable.
FIG. 4 illustrates the basic block diagram of the ground
probing radar apparatus 90. The apparatus uses a conventional
radar transmitter 92 and broadband transmission and reception
antenna but the preferred form is for the use of separate anten-
nas. It is preferred, too, for best detection ranging, thattransmitter 92 operate in a frequency range of 40 i~legahertz to
640 ~legahertz, very good results having been achieved with trans-
mitter and broadband antenna having center frequency output at
120 l~egahertz. There is, of course, some variation on best trans-
mission frequency, and this may be adjustable with considerationof the condition of the coal seam, i.e., moisture content, etc.
The apparatus 90 consists of four principal subsystems, i~e.,
transmit-ter 92, receiver section 96, control unit 98 and display
unit 100. Power and timing signals to transmitter 92 are sup-
plied by control unit 98 in like manner to prior art forms ofground probing radar. The transmitter 92, receiver section 96
and control uni-t 98 are designed in accordance with power per-
missibility requirements for in-mine usage; howevex, display unit
100 may be located at a remote position and functioning under
normal power consumption. Also, a digital computer 102, e.g.,
one of the well~known forms of mini-computer, may be sultably
disposed to receive data transmission from control unit 98 for
further processing and display.
The receiver 96 consists of a broadband antenna 104 pxoviding
input to a conventional form of radar receiver RF amplifier 108,
i ~25~
a wide band radio frequency amplifier; and, an increased signal
level output is supplied to a sampling circuit 110 such tha-t the
radio frequency signal is shifted down to a usable audio fre-
quency range at ou-tput 112. The wide band amplifier 108, Avantek
Inc., type UTO 1002, is standard and conventional radar circuitry,
and sampling circui-t 110 may be such as is u-tilized in conventional
sampling oscilloscopes and as particularly described at page 172
"Electronic Components and Measurements" by Wedlock et al.,
Prentice-Hall Inc., 1969. Such a sampling circuit is effective
to build a pulse on the order of one millisecond from a plurality
of successively delayed samples thereby to provide a much lower
frequency indication. Thus, a sample derived every 1/2 nano-
second, or 2 billion samples per second, may be effectively re-
duced to the frequency range of 5 Kilohert~.
The sampled receiver output on lead 112 is then applied to
control unit 98 which includes all circuitry for timing control
and signal processing. A timing control circuit 114 provides
system timing output to each of transmitter 92, receiver section
96 and processing circuits 116, and the processing circuits 116
provide output to a tape unit 118, display control 120 of display
unit 100, and a digital computer 102. A display indicator 122
may be any of various commercially available displays such as a
facsimile recorder, storage oscilloscope, photographic recorder
or many other of the geophysical recorder types.
FIG. 5 is a block diagram of control unit 98 in greater
detail. The control unit 98 performs three main functions; it
provides power and timing signals to the transmitter 92 and
receiver section 96; it also processes the received radar signal
wave form as supplied at input 112; and, it records the analog
and/vr digital data on magnetic tape in tape unit 12~. All of
--7--
4 ~
the various functi.ons including control of tape unit 124 are
carried out by the microprocessor circuit 126.
The timing control circuit 114 provides output leads 128
and 130 to the radar transmitter and receiver, respectively. In
addition, output timing functions are present via lines 132 and
134 to tape unit 124, and via line 136 to time gain amplifier 138,
to be further described. The range control 140 and zero time
control 142 are set by potentiometer control at the front panel
in well-kIIown manner. Range control 140 determines the length
of time that the receiver is activated, and this is presently
designed to allow variation from 50 nanoseconds to 2000 nano-
seconds. rrhe zero time control 142 is set to determine the posi-
tion of the start of the received signal relative to the trans~
mitted signal, and this may be varied from plus 500 nanoseconds
to minus 500 nanoseconds. The zero time control 142 is utilized
to help account for variable cable length between the transmitter
and receiver.
The rPceived radar signal, after wide band amplification and
sampling, is applied on line 112 into an amplifier 144 where the
return signal levPl is amplified to an amplitude capable of being
input to the recorder or tape unit 124. Amplifier 144 has two
modes of operation as controlled by an AGC switch 146. In the
ON position, AGC input is applied via lead 148 Erom microprocessor
circuit 126 as the microprocessor examines the output of the digi-
tizer and sets the gain of the amplifier so that the maximum
value or the signal is matched to the maximum allowable input to
the analog to digital converter 150. If th~ AGC switch 146 is
in the O~F position, the gain may be controlled in wel.l-known
manner by front panel control to a desired amplitude factor.
Amplified signal output ~rom amplifier 144 is then applied
--8
serially through a high pass filter 152 and a low pass Eilter
15~. The filtered signals are then applied to time gain ampli-
fier 138, as controlled by a front panel input 146 setting the
selected time gain function, and time gain amplifier 138 serves
to amplify a later portion of the trace or signal with respect
to the earlier portions in accordance with a selected ramp func-
tion, as will be described below. The outpu-t from time gain
amplifier 138 via a lead 158 can then be recorded either in analog
ormat through file marker circuit 160 to tape unit 124, or it may
be applied to analog to digital converter 150 for digitization and
input to microprocessor circuit 126, as will be further described.
Alternatively, a scan ramp generator 161 may be utilized for
signal processing within timing control 114. The scan ramp gener-
tor 161 (FIG. 7), to be further described, is utilized for a mode
of operation wherein received radar signals are stacked in accor-
dance with transmitter-receiver displacement correction, i.e.,
common reflection point stack. Thus, the offset distances for
source to receiver for each series of transmitted and received
radar signals are corrected to remove effects of source-receiver
separation, and thereafter the signals are s-tacked in micropro-
cessor circuit 126 to provide common reflection point data output.
This data operation may also be carried out in computer from tape
record output of tape unit 124.
The tape unit 124 is a variable speed cassette recorder
which has a four channel read/write capability. I'he tape unit
utilized is that which is known commercially as the PHI-DECK type
and is available from Triple I, Inc. of Oklahoma City, Oklahoma.
The tape unit 124 includes the electronices to allow ~or either
analog recording or diyital recording. In the analog mode, the
tape is driven at 3 3/4 inches per second, and one channel
~9~
5 41 ~
records the clock and start of scan pulses using amplitude
modulation while a second channel records the radar data using
frequency modulation. IRIG intermediate band parameters are
employed in well-known manner. The digi-tal record electronics
is capable of recording four traces of phase encoded data at
2800 bits per inch. The availability of two parallel sets of
electronics allows the radar operator to determine the record
mode in the field, while also allowin~ him to change the mode
of operation hy simply throwing a switch and changing tapes.
The microprocessor circuit 126 controls the tape recorder
speed whi.le also providing a data buffer for the digital read/
write electronics in the tape unit 124. The mi.croprocessor
circuit 126 also sets the file member in the file display 162 so
that the operator is apprised of that data file which is being
recorded. The record playback or tape control 164 is also
interfaced through the microprocessor circuit 126.
Microprocessor 126 receives signal input via line 166 from
analog to digital converter 150. In the digital mode of operation,
the microprocessor 126 accepts the digitized radar trace on lead
166 in order to perform further processingO The principal opera-
tions utilized within the microprocessor 126 are stacking and
compositing operations as are well-known in the geophysical trace
data processing operations. Thus, and in accordance with common
source point offsets and similar time differential considerations,
the trace data from consecutive trace signals are added -together
as they are recorded. This operation has the effect of increasing
the signal to noise ratio of the signal and al.lows for the re-
cording of what normally would be weak signals in greater ampli-
tude. Data output via line 168 is in a 16 bit forma-t, this
allo~ing for increased dynamic range as compared to analog
--10--
~ ~25~
recorded data, and a digital to analog output 168 allows for
digital to analog conversion for selected playback and display
of the digital data.
FIG. 6 illustrates each of the filter networks 152 and 154
(FIG. 5) in greater detail. Thus, whether it be a high pass or
a low pass filter, the control and switching networks are identi-
cal. A front panel thumbwheel switch 172, standard type from
EECO Inc., provldes a binary coded decimal output to a resistor
switching network 176, Siliconix type DG-201. Switc~ output is
also digitally read out for front panel indication by an LCD fre-
quency indicator 178. The respective high and low pass filters
are programmable by use of the network of resistors as the resistors
are switched into the active filter circuits to set the value of
cut-off frequency. The cut-off frequency is then displayed via
front panel LCD at frequency indicator 178. Thus, the active filter
180 receiviny signal input 182 withsignal output 184 is band pass
controlled by switching network 176. In each of the serial fil-
ters 152 and 154 (FIG. 5), the high pass filter 152 is a four-
pole Bessel filter in order to reduce ringing at the corner
frequency, and the low pass filter 154 is a four-pole Butterworth
design, both being conventional active filters.
FIG. 7 illustrates the timing control circuits 114 in greater
detail. A master clock oscillator 186 o~ well-known type and
commercially available as Connor-Winfield Type 514-R, provides
basic clock frequency output at four Megahertz on lead 188. The
clock signal on lead 188 is applied to a conven~ional type of
counter 190, a lG:l counter, type CD4520, that provides a further
reduced frequency output of 50 Kilohertz on lead 1920 Basic
clock frequency signal on lead 188 is also applled to a 8.1
counter 194, type CD 4520,which provides a 500 Kilohertz output
1 ~2~
on lead 136 for strobe of -the time gain and/or scan ramp functions,
while also applying input to multiplying digital to analog con-
verter 198, Analog Devices type AD 7541. The converter 198 then
provides a linear scan ramp output on a lead 200 and start of scan
pulse output on a lead 202. A switch 201 serves to enable a
non-linear scan ramp output by applying clock output lead 188 to
the non-linear scan ramp generator 161 (FIG. ]1) as will be further
described. This circuit is utilized for the common reflection
point stac~ing operation.
The 50 I~ilohertz output on lead 192 is also applied to a
transmit delay 204, one-shot type 74121, which provides a fixed
delay output on lead 128 to transmitter 92 (FIG. ~). The 50
Kilohertz pulse on lead 192 is also applied to a variable time
delay circuit 208, type 74121, which may be front panel a~justed
to set receiver timing. The output from delay 208 is applied to
a real time ramp circuit 210, a radar range adjustment~ The out-
put from real time ramp 210 is -then applied to one input of a
comparator 212 while the other input receives the scan ramp output
via lead 200 from converter 198. The comparator output on lead
130 then constitutes the receiver timing pulse as applied to
receiver 106. The comparator 212 may be a modulax component such
as National Semi-conductor, type LM 361, and the multiplying
digital to analog converter 198 may be such as is available from
Analog Devices, Type AD 7451.
The timing control circuits 114 (FIG. 7) provide high speed
timing signals via leads 128 and 130 to the transmitter and re-
ceiver, respectively, while also providing the time gain and scan
length signals. The received pulse from variable -time delay 208,
as controlled on front panels, determines the time of the first
received sample, i.e., pulse or minus 500 nanoseconds, with respect
-12-
1 ~2~7
to the transmit strobe pulse. The delayed receiver pulse then
star-ts a real time ramp generator 210 and the length of the ramp
is also determined by a switch on the Front panel. The real
time ramp voltage is then compared to the scan ramp voltage in
order to generate the actual receive strobe or output from com-
parator 212. The duration of the scan ramp length is generally
on the order of 100 milliseconds while the real time ramp repeti-
tion rate from ramp generator 210 is on the order of 50 l~ilohertz.
Thus, approximately 5000 transmit pulses may be used to form
a single return radar trace as the scan ramp and start of scan
pulses on respective leads 200 and 202 are utili2ed in the micro-
processor circuit 126 to control the processing of received data.
FIG. 8 illustrates the time gain amplifier 138 with analog
input via lead 214 from low pass filter 154 (FIG. 5). Clock
pulses from the scan generator or counter 194 via lead 196 (FIG. 7)
are applied to first counter 216, an 8:1 counter, which provides
output to a gain function networ]c 218. Gain function networ~ 218
is an erasable programmable read only memory (EPRO~), INTEL type
270~, and the time gain function is selected in accordance with
requisites as time gain amplifier 138 supplies audio gain as well
as the necessary time gain functions. The -time gain amplifier
rate may be controlled by one of three clock rates which are
selectable by the operator from the front panel; that is, the
selected clock rate enables the amplifier 138 to complete its
function in 1, 1/2, or 1/4 of a scan. When a scan is complete,
the counters are reset.
The output from counter 216 addresses the gain function net-
work 218 which is capable of having up to 8 time gain functions
as selectable via switch 2200 Thus, the serial output of the
gain function network 218 may be selected and gated -to outpwt
-13-
~ ~25~
with the basic clock of the gain func-tion network 218. The ga-ted
signal ou-tput from switch 220 then increments a counter 222, an
8:1 counter, which addresses a multiplying digital to analog con-
verter 224 as it receives the analog inpu-t signal on lead 214
from low pass filter 154 (see FIG. 5). As the analog signal is
applied via lead 214 to the input of converter 224, the addressing
of converter 224 causes the output on lead 226 to have a -time gain
rate applied to the analog signal. This analog signal is then
applied to a conventional form of analog switch 228 for inclusion
of range mraker signal input on lead 230 with analog output pre-
sent on lead 15~ as may be applied through file marker stage 160
(see FIG. 5) for analog recording. Range markers on lead 230 may
be generated by any of the various conventional means, e.g., a
multivibrator generator providing 20 hertz differentiated s~uare
wave output denoting the position along the radar traverse. Range
mark control also acts to control the compositing and stacking
functions by telling the processor when to record a new data trace.
FIG. 9 illustrates in block diagram the microprocessor
circuit 126. A control processor 232 accepts input from the
various portions of the control unit 98 and acts to control the
processing and recording of the radar dataO In the analog mode,
the control processor 232 only acts to control the tape recorder
unit 124. However, in the digital mode, the operator can :input
the number of traces to be stacked and the control processor 232
functions to add the designated number of traces together. Then,
when the stacking operation is comple-te, the tape format processor
234 functions to write the data to tape in tape unit 124. In the
meantime, the control processor 232 is operating to stack the
next series OL traces. The tape format processor 234 and -the
control processor 232 share a section of memory, random access
~14-
2 5 4 ~
memory 236, that is also used as the stacking and output buffers.
Further, the format processor 234 controls the speed of the tape
unit 124 (FIG. 5) so that it will be in comple-tion of a recording
cycle when the new trace is ready for recording.
Both the control processor 232 and the tape format processor
234 are presently designated as Motorola, type 6802 and the random
access memory 236 may be such as Harris, type 6504. A read only
memory 238 functionin~ with control processor 232 may be Intersil,
type 6653, 4I~ and a read only memory 240 opera-ting -through tape
forma-t processor 234 is Intersil, type 6653, 2K. Connection 166
to control processor 232 provides data input on a lead 242,
EOC/status input on a lead 244, and return of START control via
lead 246. File marker 160 (FIG. 5), via connector 248, provides
input of file number, trace number and market trace by respective
leads 250, 252 and 254. Output to a digital to analog converter
170 (see FIG. 5) is applied in the form of data output on a lead
256 with an auxiliary connection provided via connector 25~. A
gain range output on lead 260 is available for front panel indi-
cation, and lead 262 provides parallel data output, 16 lines and
strobe pulse, for input to an auxiliary computer, e.g., digital
computer 102 of FIG. 4. Output 264 from control processor 232
provides front panel processor control.
Internally o~ microprocessor circuit 126, addressed data is
supplied via lead 266 from random access memory 236 as data and
control pulse interchange is conducted on connection 26~. Control
processor 232 provides transfer o~tput to tape format processor
234 via lead 270 with return of status pulse indication on lead 272.
Tape format processor 234 then interconnects to random access
memory 236 to provide data via bus 274 with interchange of address
data on bus 276. A plurality of outputs or connec-tion 278 ~rom
~ ~ ~2~
tape format processor 234 provide the neeessary control output
to tape unit 124 (FIG. 5). Thus, tape motion, tape data, and
speed select, are provided on respective leads 280, 282 and 284
with bi-directional data as to tape data and tape status inter-
changed via conneetors 236 and 283.
~nder control of tape format processor 234, the variable
speed tape unit 124 (FIG. 5) has the capability of recording tape
at a eonstant density even though the radar unit functions at
variable data rates. Without such a feature, the tape eontroller
or tape format proeessor 234 would require either a large da-ta
storage buffer or the tape drive meehanism would require an
extremely high speed start-stop eapability. Either of these two
operations would be diffieult to aehieve in a low power unit such
as the present one which is designed for permissibility in coal
mine operations.
Tape format processor 234 functions to write an identifica-
tion block at the beginning of each series of records, i.e., files,
so that the data can be properly identified upon playback. Tape
playback ean be aecomplished by two means. First, if all of the
recorded data is played back, then the tape format processor 234
~unctions to read each digital record with output of these values
to a computer connector, i.e., from tape format processor 234
through xandom aceess memory 236 and control processor 232 for
output on conneetor 262. In addition to the disital output
capability, an analog output may be eonstructed for any display
deviee of the eonventional types which might be connected~ In the
seeond playback mode, the operator can select a desired reeord
file from the front panel and the microprocessor eircuit 126
searches the tape until the seleeted file is found whereupon data
is output in the same format until end of file is encountered.
-16-
5 ~ ~
FIG. 10 illustrates the linear scan ramp 298 as output from
multiplying D/A converter 198 ~FIG. 7) and utilized for normal
compositing operation without regard to source-receiver offset.
Thus, linear scan ramp 298, e.g. 125 milliseconds, is generated
by multiplying D/A converter 212, and a real time ramp 302 (FIG. 10)
with length equal to window length, e.g. 200 nanoseconds, is
generated in ramp generator 210 (FIG. 7) for parallel input to
comparator 212. The real time ramp 302 is repeated at the pulse
repetition rate, e.g. 50 KHz, and comparator 212 then derives
time-sliced sample output, e.g. 1~2 nanosecond duration, each
time the upsweep voltage of real time ramp 302 compares with the
scan ramp voltage 298. This is a linear sampling process effective
for pulse return compositing and random noise interference
reduction.
Both random and coherent noise rejection can be achieved
in an alternative stacking mode of operation wherein common
reception point date processing is effected. Thus, activation
of switch 201 (FIG. 7) serves to substitute scan ramp generator
161 (FIG. 11) for input to multiplying D/A converter 198 (FI~. 7)
thereby to impose a selected non-linear ramp function for the
linear time gain function, as will be further described,
An initial calibration will reveal the energy velocity in
the particular coal medium, so that energy travel times can be
continually computed for a particular source-receiver offset.
Thus, energy travel time from a given source to a selected
receiver at offset X will adhere to the equation
T =
where,
Tx equals two-way reflec-tion time for offse-t X,
-17-
~ ~2~
to equals two-way reflection time at zero (0) offset,
x is equal to offset distance, and
V is equal to velocity of the radar energy in the
particular coal medium.
The graph of FIG. 10 illustrates a non-linear scan ramp
voltage 300 with superimposition of real time saw tooth impulses
302 for a particular offset quotient, i.e. V . For a selected
scan length of 125 milliseconds r a sample on the order of 1/2
nanosecond in duration is enabled on the upsweep of every real
time saw tooth 302 as it compares with the V voltage of the
non-linear scan ramp curve 300. A distinctive scan ramp curve
300 is then available for each particular offset or V value as
selected for the particular radar survey. Thus, data input to
the microprocessor circuit 232 (FIG. 9) for the particular offset
distance X and velocity V completes the initial curve of non-
linear scan ramp 300 before energization of the transmitter-
receiver series. Data output from control microprocessor 232 is
in the form of a SEI' pulse OlltpUt 304 and an eigh-t bit binary
PRESET output on connector 306. The SET input serves to signify
commencemen-t of sampling while the PRESET data controls the curve
shape in accordance with the particular V function.
FIG. 11 further illustrates the non-linear scan ramp
generator 161 which is essentially a circuit similar to the
time gain amplifier of FIG. 8. Thus, input on lead 188a is
derived from masterclock 186 (FIG. 7) and applied to a counter
308 as applied to ramp function network 310. The ramp function
network 310 may be such as a read only memory, type 2704, that
i5 pre-programmed for the particular non-linear curve function,
e.g. as depicted in FIG. lOo Selected curve outputs may -then be
conducted by multi-position switch 312 for input to a counter
-18-
t ~ ~2~4~
314 which, in turn, provides output via lead 316 and switch 201
to the multiplylng digital-to-analog conver-ter 198 (See FIG. 7).
Converter 19~ then generates the non-linear scan ramp voltage for
input on lead 200 to comparator 212.
The counters 308 and 314 may be similar integrated circuit
devices to those utilized at the similar count positions of
FIG. 8, i.e. counters 216 and 222. SET input on lead 304 from
control microprocessor 232 is applied to ramp function network
310 to control sequencing oE the network output, and a PRES~T
]0 input, an eight bit binary input, is applied on connector 306
to counter 31~.
In FIG. 11, the counter 308 divides the master clock pulses
on lead 188a down to four ~imes the pulse repetition rate. The
ramp function network 310 contains the particular ramp function
in storage as a series of O's and l's and each clock pulse input
to ramp function network 310 causes one bit to be read from -the
memory. Thus, the succeeding counter 314 is incremented on input
of each 1 bit. The output of counter 316 is then applied to
multiplying D/A converter 198 (FIG. 7) that converts the signal
to the analog ramp voltage for application to comparator 212.
The ramp (non-linear) for each offset can be calculated
at the time the offset is shot~ or the operator can enter the
initial offset and the change in offset along with the total
number of offsets and the microprocessor can calculate all
offset scan ramps at once. The only other pieces of information
necessary for the calculation are the full scale windo~ length
and the velocity of the medium. These are readily inserted
by the operator as the velocity for the particular coal body is
pre-determined for the sounding operation.
The foregoing discloses a novel ground probing radar me-thod
-19-
t ~25~
and apparatus which is readily employed in determining the
condition and homogeneity of coal in situ. The invention may
be uti.li2ed directly at the mine face, either turmel or pillar
dispositio.n, and it enables accurate surveillance of the coal
body immediately ahead of the mining machinery. In addition,
the method and apparatus employ a signal processing scheme,
lncluding common reflection point processing, which achieve
accurate and reliable signal return at ranges heretofore not
possible.
Changes may be made in the combination and arrangemen-t of
elements as heretofore se-t Eorth in the specification and shown
in the drawings; it being understood that changes may be made
in the embodiments disclosed without departing from the spirit
and scope of the invention as defined in the following claims.
What is claimed is:
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