Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Patent
1988-07-05
1990-02-27
Tarcza, Thomas H.
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
342118, G01S 1308
Patent
active
049050087
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a radar type underground searching apparatus which detects the presence and location of objects buried in the ground such as gas pipes in the ground.
The radar type underground searching apparatus of this kind has an arrangement in which pulses of the microwave band are transmitted from the ground surface into the depths thereof and reflected waves caused by objects such as gas pipes are detected. The radar type underground searching apparatus detects the presence of objects buried in the ground by measuring peak pulses and finds the location (depth) of the objects by measuring the interval from the transmission of pulses to the occurrence of peaks of the pulses reflected.
TECHNICAL BACKGROUND
The conventional radar type underground searching apparatus has the same construction as that disclosed in the Transactions of the Institute of Electronics, Information and Communication Engineerings of '83/6 vol. J66-B No.6;713-720 in general, in which, as shown in FIG. 8, a transmitting antenna 52 and a receiving antenna 53 are arranged side by side on the ground surface 51. Pulses of the microwave range generated at a pulse generating unit 54 are transmitted into the ground 55 by way of the transmitting antenna 52 and pulses reflected by objects 56A and 56B in the ground 55 are received by the receiving antenna 53 on the ground surface 51. The pulses received are then fed to a radio-frequency amplifier unit 57 to be amplified in radio-frequency and the output from the radio-frequency amplifier 57 is utilized to detect the presence and the depth of the objects 56A and 56B.
The conventional radar type underground searching apparatus thus constructed is generally used to search for objects such as 56A or 56B which is buried under the ground at a depth ranging from several tens of centimeters to several meters. The propagation speed of radio waves (pulses) used for the search in the ground 55 is, when assuming the dielectric constant of soil is 9 for example, equivalent to 1/9.sup.1/2 =1/3 of the propagation speed in space (30 cm
s), that is, 10 cm
s. Accordingly, the time elapsed for radio waves to travel from the transmitting antenna 52 to the receiving antenna 53 by way of 56A or 56B will be very short such as 10 ns, 20 ns, or 40 ns when the depth to the objects is 50 cm, 1 m, or 2 m respectively. Different from a case where the radio wave travels through space, large attenuation in proportion to the exponent of the depth will take place when the radio wave travels through the ground 55, and the amount of attenuation may become as large as 1/3 to 1/10 in a depth of 1 m. Assuming the amount of attenuation is 1/10.sup.1/2 =1/3.16 in a depth of 1 m, amounts of attenuation in depths of 50 cm, 1 m, and 2 m are respectively 1/10.sup.1/2, 1/10, and 1/100 to show a great change. For example, when the reflected wave from an object buried in a depth of 1 m is attenuated to 1/10 with respect to the transmitted wave, the attenuation will become 1/100 for an object buried in a depth of 2 m. This makes it difficult to search for objects deeply buried in the ground.
To improve the low searching ability for the object 56B in the depths in the ground because of the attenuation of the radio wave and to make the search for the object 56B as effective as for the object 5A buried in a shallow depth in the ground, the conventional radar type underground searching apparatus has the radio-frequency amplifier unit 57 integrally provided with a sensitivity time control circuit. This circuit makes it possible, that the greater the time elapsed between the transmission and the reception of the radio wave becomes, that is the greater the depth of the object 56A or 56B becomes, the more the amplification of the radio-frequency amplifier unit 57 is made increased. Consequently, the difference of the object 56A and 56B in attenuation of the radio wave because of the difference in depth will be compensated so that the peaks of the reflected waves caused by the shallow object 56A and the deep object 5
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Kawano Akio
Tsunasaki Masaru
Osaka Gas Co. Ltd.
Sotomayor John B.
Tarcza Thomas H.
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