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According to the Defense Department report on the Persian Gulf War, these missions included 429 sorties against national command authorities, 603 sorties against command, control and communications centers, and 902 sorties against suspected nuclear, chemical and biological manufacturing sites.17 Most of these targets were shallow underground facilities or were located above ground.
However, the success enjoyed by coalition forces in the Persian Gulf War had two important consequences. The first is that the growing capability of precision guided weapons has convinced many states that they need to place their critical functions deep underground. This increases the difficulties associated with locating the facilities, decreases the ability to determine their function, and decreases the ability to destroy them. The second consequence is that destroying facilities whose contents are unknown could have serious effects on friendly forces, as exemplified by the case when US Army forces destroyed a chemical weapons bunker in Khamisiyah, Iraq shortly after the Persian Gulf war. Although the bunker was known to be a chemical weapons storage area, there was the possibility of chemical fallout within two kilometers downwind of the bunker after it was blown up. Researchers are still seeking to determine whether there is a link between veterans who suffer from health problems after the war and their proximity to the bunker when it was destroyed.18
External Design Considerations
The concept of deeply buried facilities creates an image of a structure underneath the ground that is completely hidden and isolated from view. In reality, however, complete self-containment is neither realistic nor preferred.
The reason is that most underground facilities are designed for the conduct of daily operations while remaining connected to the society's infrastructure for electrical power, water, sewage, ventilation systems, and communication systems. While some facilities can "button up" in order to operate on an autonomous basis for limited periods of time, the normal operating mode is a regular connection with the outside world. Accordingly, designers of underground facilities take prudent steps to conceal the existence of such facilities and mask their existence. While it is likely that there will be detection systems near the overburden of deeply buried facilities for discouraging intruders, a reasonable assumption is that the external features of these facilities will be designed to minimize the possibility of detection, particularly by satellites and other reconnaissance sensors.
One study reviews the capabilities of satellites to collect intelligence information about these facilities and provides suggestions for countering such capabilities.19 It suggests that concealing the facility's intended operating activities, equipment, and location from satellite observation is best accomplished by avoiding attention during the construction phase and after during its daily operations.
Another approach is to adhere to a well-planned deception scheme, which typically seeks to reduce the chance of detection by reconnaissance satellites.
These discussions are important because they provide useful insights into the potential design features of deeply buried facilities, and thus ways for avoiding the detection of underground facilities by satellites, as discussed below.
Avoid Manmade Patterns. Exhaust vents, facility entrances, and any accompanying surface infrastructure should avoid the use of square or triangular shapes. Manmade patterns should be broken up with camouflage, and camouflage should be chosen that has a high infrared (IR) signature because this is easily mistaken for natural vegetation, which normally has a high IR signature. The use of natural and confusing patterns, such as hiding equipment under cliffs and locating equipment near streams (which have thicker vegetation), offer ways to integrate the external design features of an underground facility with the natural environment, and thus reduce its detectability by satellites.
Panchromatic Deception. The reflectivity of objects on the ground is an important characteristic in determining the ability of satellites to detect an object. Therefore, the reflectivity of all surface-located support equipment, structures, and antennas can be suppressed through proper paint schemes and masking camouflage. Since black and white satellite images are most commonly used, principally because they highlight the reflectivity and contrast of objects on the ground, the paint schemes selected for surfacelocated items should use subdued tones, rather than color, to minimize its reflectivity.
Decoys. Since satellites can take stereo images, which are two slightly offset images of the same area, three-dimensional decoys can be effective in concealing the true location of the critical external support equipment for an underground facility. Furthermore, thermal heaters can be placed in mock vents to approximate the temperature of exhaust gases that an underground ventilation system would generate. These mock vents can then be placed at false locations on the surface of the earth to conceal the true location of external support equipment. Mock antenna arrays, entrances, and other features can all be replicated and thermally matched to approximate the signatures of real items, and thereby conceal the true location of a deeply buried facility.
Thermal Imaging Deception. As hot air emerges from air vents for underground facilities, satellites can see this distinctive signature. It also may be detected as hot spots that develop on the surface of the earth over various parts of the underground facility. The ambient temperature of some parts of the underground facility may elevate the temperature of parts of the surrounding earth near air vents, water pipes, emergency exits, or electrical conduits. However, measures can be taken to insulate those parts of the facility that are closest to the earth's surface. Heavy vegetation and thermal blankets can be used to reduce the thermal signatures of external components of underground facilities, and cooler ambient air can be mixed with the warmer exhaust air to minimize its detectable thermal signature.
While there are other deception techniques for defeating the capabilities of reconnaissance satellites, the previously cited study suggested that there are fundamental problems with avoiding detection by satellites. The reason is that one method for evading the detection capabilities of one type of sensor will likely be vulnerable to the capabilities of another sensor. For example, a grid of lights above a target could perfectly match the reflective signature of the surrounding area and therefore be invisible to a multispectral satellite, but this would be quite obvious to a high-resolution panchromatic sensor when viewed from an angle.20
This discussion focused on defining the two classes of underground facilities, which are known as "cut and cover" and '"deeply buried," and describing the possible design features of deeply buried facilities and the deception schemes that will serve to minimize their detection. The robust nature of the deeply buried facilities that are examined in this discussion probably represents a small percentage of the underground facilities that U S military forces might encounter in a military contingency. However, the reason for focusing on the most difficult challenges that are associated with deeply buried facilities is to give military planners the opportunity to understand how to respond properly to this difficult target. The discussion in the next section focuses on the difficulties associated with locating deeply buried facilities.
III. Locating Deeply Buried Facilities
Recent research concludes that searching for and finding underground facilities is the most important step in dealing with these targets, and that the United States must refine its capabilities for locating underground facilities.
This line of reasoning leads naturally to the question of what specific approaches and technologies will help to locate deeply buried facilities.
For background, scientists have been wrestling with this problem for decades, and have developed a variety of methods for locating objects that lie beneath the surface of the earth As shown in Table 1, modern prospectors use instruments that rely on sensing various physical properties of the earth, including geophysical prospecting instruments that measure gravitational fields, electric fields, magnetic fields or sound waves, all of which help to deduce what lies beneath the surface of the earth.21 All of these fields (and waveforms) are altered by features in the earth, including contrasts in rock density and porosity, the liquid content of the soil, or changes in naturally emanating magnetic fields due to the density or absence of material from beneath the surface of the earth (i e, underground facility) Prospecting instruments collect information by using both active and passive methods.
Table 1. Common Geophysical Methods of Prospecting source: I J won, "Diagnosing the Earth," Ground Water Monitoring Review, Summer 1990, Vol.
10, No 3 Active Subterranean Mapping Methods Active geoprospecting instruments use the emission of either sound waves or electromagnetic energy to characterize how these waves bounce off unseen objects. This is similar to the approach used by a submarine when it emits a sound (or "ping") and listens for an echo to determine the presence of a solid object. By contrast, passive instruments sense the presence of fields, such as an infrared detector that passively senses the presence of heat.22 There are two other methods, ground penetrating radar and seismic reflection methods, for locating deeply buried facilities.
A Ground Penetrating Radar (GPR) is an active device that transmits a pulse of electromagnetic energy into the ground, which when it strikes objects, is reflected back to the receiving antenna GPR is an accurate means of detecting objects that are below the surface of the earth. Under the best circumstances, GPR can penetrate about 15 feet of sand, but is completely ineffective in saturated clays and moist soils. The principal use of GPR is by archeological surveys for detecting shallow objects that are embedded in the soil as well as burial pits and trenches, so that they can develop precise digging plans that will avoid destroying artifacts. Although GPR could be used to locate electrical, water, and sewage lines that may supply a deeply buried facility, its current size, weight, limited ability to penetrate the soil, and overt operational characteristics reduce its value for high-risk military operations when discreetness, mobility, and flexibility are critical.
Seismic methods are commonly used by oil and natural gas prospectors to detect the presence of deposits beneath the surface of the earth Seismic surveys are sufficiently accurate for providing a good characterization at depths greater than 100 meters. Seismic prospecting techniques require the introduction of a shock wave into the ground, normally with an explosion or a hydraulic tamp to generate echoes for detection by precisely placed sensors.
Based on the pattern and location of the echoes, which are caused by the shock wave bouncing off underground objects, seismologists can determine the location of faults, rock density, and other underground features, including the presence of underground cavities. This approach may have some merit if it is developed into an operational capability.
For example, during the Vietnam War sensors were mounted on spikes and dropped along trails to detect the presence of enemy forces.
In this way, seismic listening sensors could be mounted on spikes and showered over an area that is suspected of containing a deeply buried facility.
The sensor spikes can be fitted with Global Positioning System (GPS) transmitters that communicate their precise three-dimensional position.
Sensor spike deployment could be followed within a short time by GPS guided munitions that are programmed to hit the ground at precise impact points. The sensor spikes could listen for the echoes and transmit this data to an orbiting aircraft or satellite for the detection and location of hollow cavities and underground structures. This concept is technologically feasible.
Passive Subterranean Mapping Methods