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Operational- and Strategic Theater-Level NBC Reconnaissance: Mapping Chemical Agents With High-Altitude Sensors.


As late as 1990, U.S. Army nuclear, biological, and chemical (NBC) reconnaissance platoons, using armored personnel carriers, identified chemical hazards with detection paper, detection kits, and chemical agent alarms. The soldiers had to be in mission-oriented protective posture (MOPP) 4, which made the procedure time-consuming as well as labor-intensive. Consequently, the information that they collected was often of little tactical or operational value when it reached an NBC center (NBCC).

By the beginning of Operation Desert Storm, however, the U.S. Army had made significant progress in fielding tactical-level detection equipment. The United States realized that the inventory of NBC defense equipment was inadequate to counter the Iraqi chemical threat, so it turned to its allies for assistance. Thanks to the Federal Republic of Germany, the U.S. Army fielded the XM93 Fox--a lightly armored reconnaissance vehicle equipped with a mobile mass spectrometer. Unlike the M113, the Fox can detect and identify chemical agents while moving. [1] This permitted the vehicle to keep up with maneuver units and provide timely information to the force commander. After Operation Desert Storm, a standoff-detection capability was added that enabled the Fox to detect and identify chemical agents at distances up to 5 kilometers.

Although these developments and others have been important, their applications remain at the tactical level of war. While enemy intentions and capabilities are generated at the operational and strategic levels, most NBC intelligence is still acquired at the tactical level. The presence of a soldier equipped with a detector, including an M21 remote sensing chemical agent automatic alarm (RSCAAL), in close proximity to a chemical agent, is presently the only means to detect an NBC hazard. Consequently, operational-level and strategic theater-level commanders are reactive rather than proactive to NBC attacks. This article describes how operational-level and strategic theater-level commanders can assume an active role in NBC reconnaissance through high-altitude, hyperspectral technology, specifically reflectance spectroscopy.

Detecting Outside the Visible Spectrum

Reflectance spectroscopy is a relatively new field, and it represents the next generation of remote-sensing technology. It is defined as "the study of light as a function of wavelength that has been reflected or scattered from a solid, liquid, or gas." [2] This article does not focus on the chemistry and physics of this subject. However, to discuss reflectance spectroscopy and its military potential, several key concepts need to be reviewed: electromagnetic spectrum, vibrational absorption, and reflectance spectrometer.

Electromagnetic energy can be described in terms of its velocity (c), wavelength [lambda], and frequency (v). All electromagnetic energy moves at the speed of light (3 x [10.sup.8] meters per second) and behaves like a wave and a particle simultaneously. It generates a magnetic as well as an electric field as it travels. It is commonly measured and recorded based on its wavelength, which is the distance from the crest on one wave to the next, and its frequency, which is in cycles per second. The relationship between velocity, wavelength, and frequency is c = lambda]v; whereas, the frequency of electromagnetic energy is inversely proportional to its wavelength. [3]

The continuum of the electromagnetic energy is the electromagnetic spectrum (see Figure 1). All energy in the electromagnetic spectrum falls within one of several regions, based on its wavelength. For this discussion, the two most important regions are the visible and the infrared (IR). Visible light consists of the electromagnetic energy with a wavelength between 0.4 and 0.7 micrometers ([micro]m). The IR region is located between 0.7 [micro]m and 1.0 mm. The regions can, in turn, be divided into bands. Blue, green, and red bands comprise the visible region; near, mid, and far bands make up the IR region.

Most molecules absorb electromagnetic energy because of their molecular bonds, which are like springs with attached weights; they can vibrate. The frequency at which a molecular bond vibrates is a function of the atomic masses of the atoms (weights) and the strength of the bond (spring). Because frequency and wavelength are interdependent, each vibration (frequency) can absorb a specific wavelength of electromagnetic energy. This phenomenon is called vibrational absorption.

The number of fundamental vibrations (frequencies) that a molecule has can be calculated based on the formula 3 (number of atoms) - 6. For example, a water molecule consists of three atoms--one oxygen and two hydrogens. Using the formula, water has three fundamental vibrations that can absorb one wavelength each. In addition, the frequencies that a molecule absorbs may vary on the physical state of the substance. For example, water in its gaseous form (vapor) absorbs electromagnetic energy at 2.663 [micro]m, 2.738 [micro]m, and 6.270 [micro]m. Liquid water absorbs energy at slightly different wavelengths: 2.903 [micro]m, 3.106 [micro]m, and 6.079[micro]m. [4]

Knowing which frequencies will be absorbed, a diagnostic absorption spectrum can be plotted for gaseous water and liquid water. The same principle also can be applied to any other substance whether solid, liquid, or gas. The plot in Figure 2 is sodium bicarbonate (Na[HCO.sub.3]), commonly referred to as baking soda. Notice that as the x-axis approaches 3.0 [micro]m, the reflectance level decreases dramatically.

The final concept is reflectance spectrometer. To detect and measure electromagnetic energy, a remote sensor, such as a reflectance spectrometer, is required. The human eye is a type of reflectance spectrometer. It can detect emitted or reflected electromagnetic energy between 0.4 and 0.7 [micro]m. The eye detects an object, a yellow flower for instance, because certain wavelengths within the visible region are not absorbed but reflected away from the flower. The flower appears yellow because the flower absorbs all the wavelengths except 0.580 [micro]m, the wavelength of yellow. [5]

Civilian Applications

Currently, high-altitude sensors are identifying specific substances on the surface of the earth through reflectance spectroscopy. As electromagnetic energy generated by the sun interacts with the surface of the earth, certain wavelengths are absorbed while others are reflected. By recording which wavelengths are reflected and comparing that data with the plots of known substances, technicians can identify and "map" minerals, plants, and even man-made materials. Reflectance spectroscopy is being used extensively in mining and forestry to locate minerals and different species of trees.

The mineral map (Figure 3) is the Summitville, Colorado, Mining District. This map was created to study the environmental impact of mining on the rivers and creeks in the area. The U.S. National Aeronautics and Space Administration (NASA) acquired the data using the Airborne Visual and Infra-Red Imaging Spectrometer (AVIRIS). AVIRIS has a spectral range from 0.4 to 2.45 [micro]m in 224 continuous spectral channels. It is mounted in an ER-2--a modified U-2 spy plane, which flies at 65,000 feet when AVIRIS is in operation. It has a swath width of 11 kilometers and a length of up to 1000 kilometers. [6]

Military Applications

"A fundamental premise of Joint Vision 2010 is that operational commanders will enjoy information superiority--the ability to see and hear virtually everything of importance in any engagement." [7] If informational superiority is vital to success, commanders should see and hear not only everything humanly possible but also everything beyond human perception as well. The military potential for reflectance spectroscopy is, therefore, unlimited. If minerals and plants can be detected, identified, and mapped, so can chemical agents such as nerve and blister. A chemical agent, like any other substance, absorbs and reflects electromagnetic energy. Once a reflectance spectrum is plotted, chemical agents can be detected, identified, and mapped just like the minerals in Figure 3.

There are several factors that would make chemical agent mapping possible. First, most chemical agents are large molecules in terms of the number of atoms. Large molecules have dozens, if not hundreds, of fundamental vibrations that equate to absorption wavelengths. For instance, VX ([C.sub.11][H.sub.26][NO.sub.2]PS) has 42 atoms. [8] According to the formula, VX has 120 fundamental vibrations, which equates to 120 different absorbed wavelengths of electromagnetic energy. Therefore, a VX spectrum plot would be easy to distinguish from other plots.

Second, all known chemical agents are organic; they contain carbon. All choking, nerve, blood, blister, and incapacitating agents have at least one carbon atom per molecule. The significance of carbon is the carbon hydrogen bond. Researchers know that this particular bond absorbs electromagnetic energy at 3.4 [micro]m.

Finally, some chemical agents contain phosphates and arsenates. All known nerve agents (GA, GB, GD, GF, and VX) contain phosphates. Arsine, a blood agent, and a few blister agents contain an arsenic atom. Both phosphorus and arsenic bonds are easy to distinguish. [9] Exact absorption wavelengths are not available.

Unfortunately, reflectance spectroscopy is limited in military applications for several reasons. First and foremost are environmental conditions; reflectance spectroscopy can take place during daylight hours only. The sun is the only source of energy at this time that can simultaneously generate the electromagnetic energy required. In addition, heavy cloud cover can prevent much of the sun's radiation from reaching the earth's surface.

Second, all chemical agents are classified as persistent or nonpersistent. Some persistent agents like mustard can take days or even months to dissipate, depending on temperature and atmospheric conditions. Nonpersistent agents can evaporate in a few minutes. Therefore, the chances of detecting a nonpersistent agent would be somewhat low.

Finally, only substances that have been plotted previously can be mapped. If a new chemical agent were employed, initially it would appear as an unknown substance until a sample could be taken and analyzed. Technicians would then compare the plots of the new chemical to the plots of known substances.

Theater-Level Employment

Reflectance spectroscopic sensors could be employed in a variety of ways to support operational- and strategic theater-level commanders throughout the spectrum of military operations. First, commanders could use high-altitude sensors to conduct NBC reconnaissance of aerial ports of debarkation (APODs), seaports of debarkation (SPODs), drop zones, and amphibious landing sites before deploying forces into the theater. Historically, forces are most vulnerable to attacks (especially NBC attacks) during the initial deployment and build-up phases of an operation. Normally, NBC defense units are not the first organizations to arrive in theater. Without NBC defense assets in theater, the ability to conduct NBC reconnaissance is very limited.

Second, high-altitude sensors can conduct reconnaissance of restricted terrain, urban terrain, and axes of advance beyond the range of tactical-level NBC detection assets. Imagine if the Iraqi army had protected its right flank with a blister agent during Operation Desert Storm. The XVIII Airborne Corps could have slowed down or quite possibly aborted its attack once its lead elements had blindly entered a contaminated area. General Schwarzkopf's "end-around" maneuver would not have achieved surprise, and 6 months of planning and preparation would have resulted in disaster for the coalition forces.

Third, operational- and strategic theater-level commanders can investigate allegations of chemical weapons use against indigenous people or refugees. During the last 25 years, there have been several confirmed or alleged uses of chemical weapons against ethnic minorities. The most notable use occurred during the Iran-Iraq War. Saddam Hussein employed a chemical agent against the Kurds, an ethnic group in northern Iraq, after he accused them of assisting the Iranians during the war. As a result of the attacks, more than 15,000 Kurds, including women and children, died.

Finally, high-altitude sensors can conduct reconnaissance of industrial sites for toxic industrial materials. A recent incident in which soldiers were possibly exposed to a toxic substance occurred in Croatia. Canadian soldiers may have been exposed inadvertently to toxic substances, specifically bauxite and PCBs, while filling sandbags during a peacekeeping mission. [10] Because the Canadians do not have a vehicle similar to the Fox, high-altitude NBC sensors possibly could have prevented this exposure.


Since 1990, the U.S. Army Chemical Corps has made significant strides to improve its chemical agent detection capabilities. It also has acknowledged that U.S. forces are the most vulnerable during initial- and early-entry operations. However, NBC defense units do not normally arrive in theater soon enough to provide force protection to initial-entry forces or contribute to the joint force commander's (JFC's) situational understanding.

For the Chemical Corps to remain a relevant member of the joint force, it must explore and, ultimately, acquire additional capabilities that will enable the JFC to reconnoiter APODs, SPODs, landing zones, and amphibious landing sites before an operation. This capability would complement, not replace, other NBC sensors--such as the Nuclear, Biological, and Chemical Reconnaissance Systems (NBCRS) and the Scanning Airborne Emission for Gaseous Ultraspectral Analysis and Radiometric Detection (SAFEGUARD)--and would eventually be an integral part of the interactive-networked detection system.

At this time, AVIRIS is probably the least expensive option to meet this requirement. Because NASA is already using it to map minerals on the earth's surface, AVIRIS would essentially be a government off-the-shelf acquisition. Not only would it meet an immediate need, but it would also serve as an interim solution and a bridge to the Objective Force.

Major Dorroh is the chief of concepts, Chemical Division, MANSCEN, Directorate of Combat Developments, at Fort Leonard Wood, Missouri. Previous assignments include deputy team chief, Defense Threat Reduction Agency, Dulles, Virginia; commander, 44th Chemical Company, 2d Armored Division, Fort Hood, Texas; DIVARTY chemical officer, 5th Infantry Division (Mechanized); Fort Polk, Louisiana; battalion chemical officer, 4th Battalion, 7th Field Artillery Regiment, and assistant brigade chemical officer, 42d Field Artillery Brigade, Giessen, Federal Republic of Germany. Major Dorroh is a graduate of the Chemical Officer Basic and Advanced Courses, Combined Arms and Services Staff School, the Defense Language Institute, and the Canadian Command and Staff College. He holds a bachelor's in biology from the University of North Alabama, Florence, Alabama, and a master's in West European studies from Indiana University, Bloomington, Indiana.

[Graph omitted]


(1.) Department of the Army, Field Manual 3-3, Chemical and Biological Contamination Avoidance, Washington, D.C.: Government Printing Office, 1992, p. 3-6.

(2.) Roger N. Clark, About Reflectance Spectroscopy, (, 13 November 1998.

(3.) Floyd F. Sabins, Jr., Remote Sensing: Principles and Interpretation, 2nd edition; New York: W.H. Freeman and Company, 1987, p. 3.

(4.) Clark.

(5.) Ibid.

(6.) Trude V.V. King, et al, Remote Mineral Mapping Using AVIRIS Data at Summitville, Colorado and the Adjacent San Juan Mountains, (, 18 November 1998.

(7.) Thomas Behling and Kenneth McGruther, Planning Satellite Reconnaissance to Support Military Operations: A New Doctrine, (,7 December 1999.

(8.) Department of the Army, Field Manual 3-9, Potential Military Chemical/Biological Agents and Compounds, Washington, DC: Government Printing Office, 1990, p. 24.

(9.) Clark.

(10.) "Inquiry Begins Digging Into Toxic Mystery," Halifax Herald Limited, ( +Canada), 28 August 1999.
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Title Annotation:nuclear, biological, and chemical
Author:Dorroh Jr., Gerald (Neal)
Publication:CML Army Chemical Review
Geographic Code:1USA
Date:Aug 1, 2001
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