Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
2000-07-03
2002-12-17
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S179000, C342S191000
Reexamination Certificate
active
06496136
ABSTRACT:
BACKGROUND OF THE INVENTION
Trees suffering from internal decay, which reduces the amount of solid wood, are weakened structurally and are potential hazards to both property and people if they fall due to an external force, such as wind. This is especially true in urban areas. One of the key contributors to this hazardous condition is the existence and extent of internal decay. Decay can be classified into three broad categories: (1) early, in which a region of the solid wood becomes “pulpy” and “mushy”, (2) moderate to advanced, in which the wood begins to separate and small pockets of air (“gaps”) develop, and (3) total, in which no remaining wood exists in the decay region, only an air pocket. If decay is present, and its extent can be estimated, the amount of remaining wood can be calculated and used by tree diagnosticians, such as certified arborists, to assess the hazard posed by the distressed tree.
Since a tree is rarely circularly symmetric and internal decay is rarely at the dead center position, it is important for any inspection technique to be able to examine the tree at various circumferential location points to adequately map out the decay location and geometry. The decay pocket is more accurately described as the number of interrogation points increases, with the ultimate description deriving from a continuous or nearly continuous scan. Once a number of interrogation points have been tested, a cross-sectional view of the tree's interior is constructed and used to estimate the decay and remaining solid wood amounts.
A number of inspection techniques are commercially available that are capable of either detecting or mapping internal decay. One example of the means for detecting decay involves a procedure for using changes in the electrical impedance, or resistivity, of the tree to infer the presence of a void. Another example involves using a vertical array of accelerometers, mounted on large nails pounded into the tree, and examining the relative amplitude ratios of the accelerometer outputs after a hammer blow is applied above the topmost accelerometer position. A structurally sound tree, with no decay, is “stiffer” than one with some decay present and resonates at a different, generally higher, frequency. Those techniques rely on the concept of the weakened structure producing responses that are different from a solid structure. The advantage of those techniques is that they are non-invasive, but their disadvantage is that they are only moderately accurate for decay detection and cannot provide a cross-sectional image.
An example of an existing means to detect and map internal decay is an automated drilling device. Here, the inspector simply holds the drill against the tree at some circumferential location and depresses the trigger. A long, thin drill bit is slowly advanced into the tree by a motorized drill and a strip chart output is produced that plots the motor torque required to advance the drill as a function of the distance drilled. The chart is then examined to see if the torque decreased at some distance into the tree, which indicates an area of lesser resistance to drilling—i.e., a decay pocket—and its extent can be accurately mapped. Multiple holes must be drilled around the tree's periphery to insure that the decay is found, since it may not be at the dead center position, and to obtain a reasonable estimate of the size and shape of the decay pocket. There is a practical limit to the number of holes that one can drill, and, consequently, the cross-sectional view produced by this technique is fairly coarse. The advantage of this technique is that it is capable of producing a cross-sectional view, but its disadvantage is that the price paid for this view consists of multiple holes needing to be drilled deep into the tree's interior to obtain only a coarse cross-sectional view.
Another example of an existing means to detect and map internal decay is using a pair of low-frequency ultrasonic transducers operating at center frequencies in the range of 50 KHz to 250 KHz in a diametrically opposed transmission inspection mode. That procedure has been used successfully for inspecting utility electrical poles for internal decay. In principle, the opposing transducer pair can be moved to different points around the circumference, and an ensemble of through-transmission ultrasonic waveforms can be recorded from these locations and used to create a cross-sectional image (with special software). That technique works fairly well for utility poles primarily because utility poles have no bark, are circularly symmetric, and have small diameters (compared to trees). That technique has not worked for trees.
As indicated by its name, ground penetrating radar (GPR) systems are used quite extensively at present to make measurements of different structures in the ground. These systems are also referred to as impulse radar systems. Example applications include searching for buried utility lines in the ground, determining the location of reinforcing bars in concrete, examining for defects in roadbeds, and searching for the existence of buried structures in archaeological surveys. GPR systems incorporate a transmitter having an antenna that radiates or emits a short pulse of radio frequency electromagnetic energy, typically in the frequency range from 1 MHZ to 10,000 MHZ (10 GHz), into the subsurface medium. GPR systems, compared to other radar systems, are characterized by being able to generate a pulse length which is short with respect to the wavelength of the center frequency being transmitted. In practice, a pulse of 1 to 2 cycles of the center frequency can be emitted.
The GPR method involves the transmission of high frequency electromagnetic radio (radar) pulses into the earth and measuring the time elapsed between transmission, reflection of a buried discontinuity, and reception back at a surface radar antenna. A pulse of radar energy is generated on a dipole transmitting antenna that is placed on, or near, the ground surface. The resulting wave of electromagnetic energy propagates downward into the ground, where portions of it are reflected back to the surface when it encounters buried discontinuities. The discontinuities where reflections occur are usually created by changes in electrical properties of the sediment or soil, variations in water content, lithologic changes, or changes in bulk density at stratigraphic interfaces. Reflections can also occur at interfaces between archaeological features and their surrounding soil or sediment. Void spaces in the ground, such as may be encountered in burial tombs, tunnels, or caches, will also generate significant radar reflections due to changes in radar wave velocity between the medium (i.e., ground) and the air inside the void.
Whenever there is a change in the electrical properties in the medium, part of the pulse is reflected and part of the pulse continues to propagate into the medium. So waves or pulses are reflected by reflective interfaces defining upper and lower margins of a subsurface structure or anomaly. The reflected pulses are detected at the antenna of a receiver. The 2-way travel time, t, from emission to detection is measured and the distance of the target from the source, d, can be determined using the following equation:
d=
(½)
v t
(1)
where v is the radar velocity in the medium and the factor ½ compensates for the two-way travel time between antenna to reflector and back to antenna.
The depth to which radar energy can penetrate and the amount of definition that can be expected in the subsurface is partially controlled by the frequency of the radar energy transmitted. The center frequency of the transmitted radar energy controls both the wavelength of the propagating wave and the amount of weakening, or attenuation, of the waves in the ground. The detection resolution of subsurface targets is a function of the pulse length and, hence, of the radio frequency (or wavelength) of the radar signal. Shorter pulse lengths (i.e., high frequencies) provide bette
Creighton Wray James
Narasimhan Meera P.
Sotomayor John B.
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