Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
2002-09-27
2004-02-10
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S196000, C342S027000
Reexamination Certificate
active
06690316
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to automated detection and alerting to the presence of hidden structure. More particularly, it provides a low-cost, fully integrated, mobile, early warning system for continuous detection and early warning of bridged crevasses. For certain applications, it may be solar powered with battery backup, with an option for at least one battery to be solar rechargeable.
BACKGROUND
Bridged crevasses present a challenge and hazard to parties traversing ice streams and glaciers in the Antarctic, the Arctic and elsewhere. While an open crevasse is usually visually discernible and therefore avoidable, there is little or no visual cue to the presence of a bridged crevasse or to the thickness of the overlying snow bridge. When in terrain where there is probable occurrence of bridged crevasses, progress is inhibited; parties remain roped together and travel slowly and deliberately. Personnel are at risk of injury or death if a snow bridge is unwittingly breached. Secondarily, loss of vehicles, sleds and equipment may occur.
The current state-of-the-art for bridged crevasse detection, warning, and spatial parameter quantification consists of two methods. Probing is a low-tech solution requiring a securely roped individual to carefully approach a suspected snow bridge and repetitively insert a long, thin wand deep into the snow, feeling for an underlying void. This “dipstick” approach can provide an approximate indication of the thickness of a snow bridge and the horizontal extent of the underlying abyss. The second method is an application of ground penetrating radar (GPR). This application has been discussed in the literature and has seen limited use in several forms for many years. Recent applications of this technique have been quite successful in locating bridged crevasses in the path of over-snow vehicles. The conventional GPR alternative, typically using a research-grade radar system, is hi-tech, expensive, requires a trained operator to interpret, and thus is used less frequently. In a typical application, a GPR antenna is positioned on a long boom ahead of the traversing vehicle or party. Electromagnetic pulses are transmitted in a broad antenna lobe pattern having vertical and some near-horizontal components. These pulses reflect from underlying snow and firn density boundaries, i.e., a boundary indicative of a dielectric contrast, and refract from the near-vertical walls of proximate crevasses. The boundary between the snow, firn or ice, and the air-filled void of the crevasse provides a strong dielectric contrast and reflector and refractor of electromagnetic energy. The typical radar signature (return) of snow and firn stratigraphy
100
devoid of crevassing is a series of nearly horizontal layers appearing as horizontal traces
102
below the surface
101
on a profile image as shown in FIG.
1
. If a crevasse is encountered, the crevasse radar signature
200
is displayed as a convex hyperbolic curve
202
, the apex being directly over the crevasse and the “tails” trending deeper into the snowpack as shown in FIG.
2
.
FIG. 3
annotates the “crevasse signature”
200
of
FIG. 2
with a dashed line
301
to delineate the crevasse. Note that this crevasse signature
200
is intermixed on the display with the stratigraphic signature
100
depicted in FIG.
1
.
Conventional GPR operation while traversing suspect snow and ice fields employs a trained operator constantly observing a radar display to discern the hyperbolic crevasse signatures
200
, halting traversal as the convex hyperbolic curve
202
appears on the display. This important activity is manpower intensive and is subject to a high fatigue factor with resultant dire consequences if not carefully monitored. Automating bridged crevasse proximity detection and warning using a low-cost designed-for-purpose radar system has positive implications for safety, economics and efficiency. It may be applied to scientific, search-and-rescue, industrial and commercial trans-glacial traversing in the Antarctic, the Arctic, and elsewhere.
A preferred embodiment of the present invention provides an automatic, portable, inexpensive, designed-for-purpose, crevasse detection system that is easy to operate and may be applied to field party and general snow field traversal scenarios to include diverse activities such as identifying the snow cave of a polar bear for investigation by a wildlife biologist.
SUMMARY
An inexpensive system integrates the front-end of a commercial-off-the-shelf (COTS) ground-penetrating radar, a COTS personal computer (PC), and a specialized algorithm to alert to geospatial anomalies in real time. The alert may be aural, indicating the relative proximity of a geospatial anomaly. The system may also include a visual alert that indicates the relative proximity of a geospatial anomaly, or both an aural and visual alert.
In a preferred embodiment, the geospatial anomaly of interest is a crevasse, in particular, a bridged (hidden) crevasse. The bridge may result from accretion of snow, ice, firn, or any combination thereof.
In a preferred embodiment, the radar front-end is an FM-CW radar front-end, comprising an antenna (although multiple antennas may be used), a transceiver incorporating a circulator, a local oscillator, and a mixer.
In a preferred embodiment, the processor is a personal computer that incorporates at least a low pass filter (LPF), a high pass filter (BIF), an analog-to-digital (A/D) converter, a digital signal processor (DSP), and a display, such as a CRT or a liquid crystal display (LCD). For aural alerts, the PC further incorporates a sound card connected to at least one speaker.
The specialized algorithm processes returns from operation of the radar front-end in A and B parallel channels to establish a running average of vectors in the A channel for comparison to each single vector being processed currently (and concurrently) by B channel, such that the comparison permits detection of a spatial anomaly within a target volume illuminated by the radar front-end.
Also provided is an inexpensive method of detecting spatial anomalies within a target volume, the anomalies not otherwise evident without use of methods that are expensive, time-consuming, or both. A preferred embodiment of the method comprises:
illuminating a target volume with electromagnetic energy;
using circuitry to derive audio frequencies representing reflections of the electromagnetic energy;
establishing vectors representing the audio frequency versions of the reflected energy in A and B parallel channels, such that a running average of the vectors is maintained in channel A for comparison to a current vector being processed in channel B; and
using this comparison to initiate an alert.
The cost of equipment for this processing is minimized through down conversion to audio frequencies prior to processing.
In a preferred embodiment, the anomalies are voids otherwise hidden from observation. Of particular interest are voids representing crevasses hidden by accretion of snow, ice, firn, and any combination thereof. Methods are provided to provide an alert aurally, visually, or as a combination of both.
Aural alerts are established by processing scaled signals in parallel to establish the frequency and volume of the aural alert. Visual alerts are established by:
subtracting the running average vector of channel A from the current vector processed in channel B;
filtering the result of the subtracting to remove spikes that cause “speckle;”
stacking by m, a whole number, the filtered result to achieve a stacked value,
clipping the stacked value to eliminate any amplitude variability that may introduce adverse effects;
peak extracting the clipped stacked value to establish a bin number for it, the bin number providing an estimate of distance to a nearest edge of the spatial anomaly;
using the bin number to drive a visual alarm function; and
displaying a visual alarm.
There are several advantages to a preferred embodiment of the present invention:
self-monitoring standoff geospatial
Baugher Jr. Earl H.
Sotomayor John B.
The United States of America as represented by the Secretary of
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