Electronic Warfare. Electronic Support

Introduction. Over the last century, there has been a burgeoning use of the electromagnetic (EM) spectrum for military purposes, including those related to communications, navigation, and targeting.

This dependence is embedded in many modern warfare doctrines and technologies, such as:
- Revolution in military affairs;
- Network-centric warfare;
- Information warfare;
- Rapid decisive operations;
- Intelligence, surveillance, target acquisition, and reconnaissance;
- Precision guided weapons.

Given the importance of the EM environment to military operations, there is obvious reason for safeguarding its use by friendly forces, denying its use by enemy forces, and defeating enemy efforts to achieve the same objectives. Electronic warfare (EW) encompasses the broad and somewhat ill-defined mix of military tactics, techniques, procedures, technology, and organizational structures that address these concerns (1,2). It is also related to some civilian technologies and applications, which include spectrum monitoring and radio astronomy.

Historical experience has repeatedly demonstrated the importance of EW as highlighted by an extensive body of declassified information that pertains to operations by both sides in World War II (WW2)(3-5), and by more recent accounts concerning the Korean, Vietnam, Six-Day and Yom Kippur Wars, and the campaigns in the Falklands, Lebanon, Kosovo, Chechnya, and Iraq (6-11).

EW continues to be widely recognized as a powerful force multiplier, and the development and application of EW concepts and technologies consequently remains a high priority (12,13). For the greatest effect, its use is regulated by planning structures that tailor it to situational requirements and procedures intended to deny the enemy as much knowledge as possible relating to its specific capabilities and deployment structures. For this reason, many aspects of EW are highly classified.

Formally, the roles of EW are subdivided into:
1. Electronic support (ES) - taking advantage of signals emitted by an opponent’s systems;
2. Electronic attack (EA) - degrading the ability of an opponent to use his systems;
3. Electronic protection (EP) - safeguarding the effective operation of friendly force electronic systems against enemy EA and ES activities.

The following article presents a breakdown of EW in this order, with attention given to both technical system concepts and relevant operational doctrine.

Electronic Support. ES, which is also known as electronic support measures, concerns the sensing of communication, radar, and other electromagnetic signals of potential interest. ES sensors perform the following technical functions:

1. Signal detection - determining the presence of a signal;
2. Signal classification - associating the signal with a type of modulation or function;

3. Signal parameter and feature extraction - measuring various signal parameters; such as carrier frequency, power, transmission start and end times, and bandwidth;
4. Emitter identification - determining the type of system that the signal is associated with;

5. Signal intercept - recovering the message content from communication signals;
6. EW analysis - inferring the organization and structure of enemy networks, dispositions of forces and operational intent from communications traffic patterns and message content;
7. Geo-location - determining the positions of signal emitters.

Several points concerning ES deserve emphasis. First, its passive nature has the great advantage that valuable intelligence can be produced without an adversary being aware. Second, the mere suspicion of its use can cause an adversary to restrict its use of communication systems and active sensors, which thereby reduces their operational value. Finally, radar ES systems often can detect a radar transmitter at ranges considerably in excess of the useful range of the radar (14).

The organization and processing of information provided by ES sensors is a complex problem. Much value of ES sensor outputs can be lost if information does not reach the appropriate commanders and other potential users in a timely way. Complicating factors include the volume of information, the difficulty of interpreting it, and the need to protect sensitive information concerning ES capabilities.

The last point is a very real concern. During WW2, the decryption of German communication signals coded with the Enigma cipher provided immensely valuable intelligence to the British. Accordingly, every effort was made to avoid arousing suspicions that the Enigma cipher was anything other than unbreakable. For example, reconnaissance aircraft would be dispatched to ‘‘find’’ an important convoy whose orders had in fact been revealed by the decryption of Enigma messages, which thereby gave the impression that the attack that followed was the direct result of routine aerial reconnaissance (5).

The diversity of the roles performed by ES systems has resulted in a significant degree of specialization in the design of the systems themselves and their organization and control.

Tactical ES. Tactical ES is the deployment of an ES capability in direct support of field operations. It typically resides within some form of dedicated EW unit that may be either part of the maneuver force’s echelon or assigned to support it under an operational (OPCON) or tactical (TACON) command and control relationship. Examples of tactical ES are found in land, air, and sea operational environments, where objectives include:

1. The intercept, direction finding, and analysis of battlefield communications signals by ground-based assets to determine the composition and geographical distribution of enemy forces and the immediate intentions of its elements, from fighter to commander. When ES is performed by an EW unit native to the maneuver force, “intentions and warnings’’ tip-offs are reported directly to field unit commanders and their staff. The unit may also acquire and disseminate intelligence for consumption strictly within Signals Intelligence (SIGINT) channels (see below) and generate technical information for internal process refinement;

2. The detection and direction finding of battlefield surveillance radars by ground-based radar ES;
3. The detection and analysis by a radar warning receiver (RWR) of radar signals associated with enemy target acquisition, tracking, and fire control systems, to provide aircraft pilots with situational awareness and warnings of threats. This information is essential for the timely initiation of suitable countermeasures, which may include a combination of EA and evasive maneuvers;

4. A general surveillance capability by a warship’s radar ES systems to track military, merchant, or clandestine ships and fishing vessels using the signals received from their navigation radars. These systems also support self-protection functions against radars associated with threat weapon systems. On larger platforms, there are usually more provisions for analyzing ES information, fusing it with other intelligence, and distributing it to other platforms, channels and organizations (including SIGINT).

The capability to geo-locate transmitters associated with communication, navigation, and radar systems is particularly important; even approximate indications of the direction of an enemy position or platform provided by direction finding (DF) are valuable from a situational awareness perspective. Estimates of the positions of individual emitters can be determined by obtaining lines- of-bearing from spatially separated sites and solving for the positions where they intersect. Geo-location is particularly important for communication signals when the message content cannot be extracted because of encryption or other techniques. Appendix 1 provides an overview of various DF techniques that can be used for the geo-location of signal sources by ES systems.

An additional EW analysis (EWA) capability is often associated with units that deploy ES assets. EWA is a military intelligence function that specializes in drawing operational inferences from EW data. Its main purpose is to determine the enemy’s ‘‘electronic order of battle,’’ which is a comprehensive representation of its electronics systems, including their identification, geographical disposition, and where possible the association of this equipment with specific units within a command-control structure. An EWA cell may also be responsible for maintaining communication target lists and selecting information for dissemination to Intelligence organizations.

Tactical communications ES is a particularly challenging problem in urban environments. Multipath propagation effects can be expected to degrade the accuracy of radiofrequency direction-finding systems. Furthermore, opposition forces can be expected to make use of the civilian communications infrastructure, which results in a requirement to sift rapidly through a large amount of communications traffic to find the signals of interest.

Signals Intelligence. SIGINT is the strategic application of ES performed under the control of national intelligence organizations, such as the National Security Agency in the U.S., and the Government Communication Headquarters in the U.K.

The term relates variously to the type of information produced, the systems used to produce it, and to the community that controls the ES systems and the analysis and distribution of their products. SIGINT ‘‘products’’ are disseminated via highly classified channels and, except in exceptional circumstances, are released only for use in the wider national or Military Intelligence communities after being ‘‘sanitized’’ of any distinguishing elements that could reveal the source. On the battlefield, there may be some overlap between SIGINT and tactical ES activities and platforms, with EW units sometimes tasked to serve both functions simultaneously.

SIGINT comprises communications intelligence (COMINT) and electronic intelligence (ELINT). COMINT is concerned with the message content of communication signals, information about communication traffic patterns, and the locations of the associated transmitters, with a strong emphasis on determining higher-level or ‘‘strategic’’ command and control structures. ELINT is the collection of technical or ‘‘parametric’’ information about the radar and other non-communications equipment (15).

ELINT has several important uses. First, theoretical analysis of the signal parameters allows inferences to be drawn about the functions, capabilities, and limitations of the systems associated with the signals, and hence, more broadly, about enemy early warning or targeting capabilities. Second, ELINT data are used to construct emitter libraries or databases that are fundamental to EA and EP operations.

For each known type of radar, information is collected on the signal parameters for the various operating modes, the estimated radar performance, its intended function(s), and the platforms the radar is known to be installed on. An ES system on a ship or tactical aircraft correlates the parameters of observed signals with the database entries to identify the radar systems that transmitted them, and, if an observed signal is associated with a threat, it provides the information needed to select and execute the most appropriate countermeasures.

SIGINT operations often involve the use of specialized equipment deployed on either dedicated or multiuse platforms, which include satellites, ships, and aircraft. During the Cold War, suitable types of aircraft were extensively modified to perform SIGINT. By operating at altitudes of 10 km or higher, useful ranges could be extended to hundreds of km for the intercept of microwave radar signals. Consequently, intelligence could be acquired from aircraft flying at the periphery of the Soviet defense perimeter.

For a period, specialized high-altitude aircraft could even conduct operations over Soviet territory by flying above the effective ceiling of interceptor aircraft and ground based antiaircraft weapons. After improved Soviet antiaircraft defenses made over flights impractical, the West hurriedly deployed satellite-based systems (16).

In recent years, much interest has been aroused by the idea of integrating ES information derived at different levels (tactical, operational, and strategic) by EW and SIGINT units with similar objectives, but possibly different reporting mechanisms. For instance, modern strategies for Netcentric Warfare involve the accumulation of various kinds of data and intelligence at a central point where it can be fused to produce more complete assessments. However, many practical challenges exist in reconciling technical possibilities with doctrine.

Complicating factors and risks involved with centralized analysis schemes include:
1. The quantity of data generated by advanced ES systems may tax the analysis systems that must sort through it;
2. Delays in the reporting chain, where key information may take longer to reach its ultimate destination after passing through a central accumulation point;

3. The expense and complexity of deploying communication systems with adequate bandwidth;
4. Standardization issues for technical interfaces, and the complexity of both designing and maintaining interfaces for systems that were originally designed for different purposes and may be based on widely differing technologies;

5. Complications that affect the handling and distribution of information resulting from classification issues and, in the case of multinational environments, the willingness of individual nations to declare and release their information to others;

6. The risks of commanders relying too heavily on the formation of a ‘‘complete intelligence picture’’ in lieu of trusting their judgment and intuition, which can lead to decision paralysis.