What are the defense applications of electro-optical sensors?

Electro-optic sensors span a wide range of technologies, from various types of imaging devices to infrared (IR) detectors. They are used for various defense applications that enhance situational awareness, including intelligence, surveillance, and reconnaissance (ISR), search and rescue, threat detection and target identification, and protection against IR-guided missiles.

Electro-optic and IR (EO/IR) sensors convert electromagnetic energy like visible and IR light into electronic signals that can be analyzed to learn important details about their source, including their position and speed. Unlike radar, which relies on emitting and detecting high-frequency electromagnetic radiation, EO/IR sensors are passive devices and help the user avoid detection.

The U.S. Space Force’s Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) system uses telescopes equipped with EO/IR sensors to track objects in deep space. EO/IR sensors also track terrestrial objects from orbiting satellites.

EO/IR sensor fusion

Many systems incorporate both EO and IR technologies. Common wavelengths include the visible spectrum, mid-wave IR (MWIR) from 3 to 5 µm for long-range thermal surveillance, which can detect small targets in challenging weather conditions, and the short-wave IR (SWIR) spectrum, which ranges from 0.9 to 2.5 µm and can produce high-contrast images in adverse weather conditions, such as fog, haze, rain, and dust.

Some advanced systems implement hyperspectral imaging (HSI), which combines conventional visible light imaging and spectroscopy to collect and process information across the electromagnetic spectrum. Compared with multispectral imaging, HSI can provide more detailed information.

The benefit of fusing technologies is the ability to detect and identify potential threats during all visibility conditions, such as day and night, and through otherwise obscuring atmospheric conditions. EO/IR systems can also provide a detailed 360-degree picture of the surrounding environment.

A shipboard panoramic electro-optic/Infrared (SPEIR) system is being fielded that enables passive (no radar emissions) detection of anti-ship cruise missiles, fast attack craft, fast inshore attack craft (FIAC), unmanned aerial vehicles (UAVs), periscopes, and mines. SPEIR has a wide field of view (WFOV) with three MWIR cameras and three full-color cameras mounted on a single three-axis stabilized pedestal, as shown in Figure 1.

Figure 1. This naval SPEIR system provides a detailed, real-time, 360-degree picture of the surrounding area. (Image: L3Harris Technologies)

EO/IR technology like SPEIR uses sophisticated software to analyze signals based on size, motion, optical characteristics, and other factors. The software includes a database of distinct electromagnetic fingerprints for various objects. This enables better target discrimination and identification even in a cluttered and congested environment.

It can identify objects as small as one to two pixels on a screen, including fast–incoming targets such as anti-ship cruise missiles, FIACs, and UAVs.

The system uses a modular open system approach (MOSA), which divides it into distinct functional modules, such as sensors, processing units, and displays. Each module has a defined interface, allowing for independent upgrades or replacements. Model-based system engineering (MBSE) supports continuous improvements in system operation.

Going ashore and getting airborne

EO/IR sensors are also used in fixed and mobile ground-based installations and onboard aerial platforms, such as fighter jets, drones, and helicopters. When mounted on aircraft, UAVs, and helicopters, they can be used for surveillance missions.

Airborne surveillance sensor suites are often integrated into stabilized and interchangeable pods. Some designs are highly directional. Instead of providing a 360-degree view, they include a laser “pointer” that enables the operator to control the direction of the field of view and investigate specific locations.

The sensor suites can be complex and include a high-definition (HD) MWIR thermal imaging camera with continuous zoom, an HD multispectral zoom video camera, and a SWIR spotter camera, which provide additional multispectral capabilities, especially under conditions of challenging visibility. The near-infrared (NIR) laser pointer improves operational flexibility and efficiency (Figure 2). Models with a laser designator/distance detector (LDR) are also available for target marking and ranging measurements.

Figure 2. This EO/IR sensor pod can be mounted on an airborne platform and used for surveillance missions, marking, and ranging targets. (Image: Hensoldt)

Summary

EO/IR sensors have many applications in aerospace, naval, and ground-based defense environments. They can use various sensor technologies, such as visible light, NIR, MWIR, and SWIR, as well as hyperspectral and multi-spectral imaging. A key advantage of these technologies is their passive operation, which makes them undetectable to an opponent.