Littoral warfare

Littoral warfare comprises two aspects of military operations near large bodies of water:

1. Seaward: the area from theopen ocean to the shore, which must be controlled to support operations ashore.
2. Landward: the area inland from the shore that can be supported and defended directly from the sea.

Littoral warfare, sometimes called "green water" operations, is distinguished from "blue water" operations far from land, and "brown water" operations and other military activity on rivers and other inland waterways. In today's geopolitical environment, "green water" of coastal areas of ocean, and "brown water" on inland waterways, jointly forming the "littoral", create new challeges for modern ships in shallow water of the littoral . During the Cold War, the navies of major naval powers were optimized for blue water warfare. This meant that units such as aircraft carrier battle groups would spread out circular formations hundreds of mile in radius, when airborne early warning or airborne warning & control and long-range fighter aircraft. The ocean was sufficiently deep that submarines rarely, if ever, to wait silently on the bottom.

There are major differences in littoral warfare. Even relatively small powers can deploy extremely quiet battery-operated submarines on the seafloor, which rise and attack only when major vessels are in range. Small craft, including suicide speedboats, can hide on the coast, and attack with very little warning.

In the littoral, there will be threats not encountered in the open ocean. In the planning for the WWII invasion of Japan, there was awareness that kamikaze tactics would not be limited to airplanes. Explosive-laden speedboats hidden along the coast, or small submarines silently on the bottom, could rush out, at close range, and ram naval vessels. The 12 October 2000 attack on the USS Cole, in a harbor, was only by one boat; consider that in the Iran-Iraq War, waves of teenage volunteers ran into minefields to clear them for the real soldiers following.

Not all threats need be suicidal. Computer-controlled mines can appear to be one more large boulder on a rocky bottom, until a ship comes into range. Modern naval mines are not limited to explosive charges to which the target comes; the U.S. Mark 60 CAPTOR mine, while intended for antisubmarine warfare in the deep ocean, is an example of what can be done. When the CAPTOR senses a target, it releases a Mark 46 lightweight torpedo, the same that an antisubmarine helicopter would drop, which actively chases its prey.

Since littoral operations often involve amphibious warfare, ranging from brief reconnaissance to major invasions, the characteristics of the approach to the beach, and the beach itself, are critical. Landing craft, for example, need to know about underwater obstacles (e.g., the "D-Day" landings at the Battle of Normandy were made at low tide, to reveal obstacles) and unusual tides (e.g., at the Battle of Tarawa). If vehicles are to go ashore, the bearing strength of the beach must be known.

Antisubmarine warfare

Acoustic

Since acoustic sensors (i.e., passive hydrophones and active sonar) perform less effectively in shallow waters than in the open seas, there is a strong pressure to develop additional sensors to find targets. . The acoustic sensors will need correction from sensors that measure water characteristics. Several new technologies will be needed for shallow-water naval operations These will have to be coupled with sensors that give information on the water conditions of the littoral, which vary much more than in the deep open ocean. For example, in blue water, the bottom may be so deep so that it is out of sonar range and will give no acoustic reflections. In the littoral, not only will there be bottom reflections, but the bottom depth and texture will change with tides, seasons, and marine life.

Electro-optical

One family of techniques, which will require electro-optical sensors to detect, is bioluminescence: light generated by the movement of a vessel through plankton and other marine life. ref name=NASCGER-91 />

• Bioluminescence
• Wake effects (also see SAW radar)

Magnetic

Magnetic anomaly detection (MAD) has long been used as one of the final techniques used by antisubmarine aircraft to localize a submarine prior to releasing weapons to kill it. MAD was of marginal use in blue-water operations, as it will not detect a deep submarine, even though the aircraft flies dangerously low. In the littoral, however, MAD may be confused by bottom debris, decoys and anything else that changes the magnetic field of the earth.

This SBIR Phase I proposal describes the development of a conceptual design for Matched-field Gradiometer Processing (MGP) for ASW, an advanced processing approach capable of taking advantage of recent and pending advances in ultra high-sensitivity scalar laser magnetometer development for airborne and undersea ASW. This matched-field approach to magnetic gradiometer processing for magnetic anomaly detection in ASW systems will provide unprecedented precision in magnetic noise reduction, detection, target parameter extraction, localization, and prosecution/tracking. Under this SBIR project, the processing of magnetic sensor data will be defined to provide target information and identification never before accomplished in real-time operation. Advanced noise reduction methodology will be developed to improve and enhance detection and localization of sea and land targets. Under this Phase I Project, the feasibility of implementing this advanced algorithm for operational use in Phase II will be established. Benefits: Matched-field Gradiometer Processing can provide an unparalleled advance in a variety of commercial and military applications including measurement of the magnetic fields in the human body. Moreover, MGP can also be used with an ELF communications receiver. Superior noise reduction and signal component extraction capabilities of the MGP, in conjunction with high sensitivity advanced magnetometers, make possible high performance, short or long baseline gradiometers for use at the Earth's surface in airborne and surface geomagnetic prospecting as well as unexploded ordinance detection (UXO). MGP complements the laser magnetometer technology currently being developed by the US Navy for submarine detection and mine countermeasures applications. MGP will produce highly accurate and complete parametric signature analysis of magnetic signals detected for a variety of applications in commercial security and surveillance applications. Furthermore, MGP is ideal for geological exploration and mapping, underground and undersea cable/pipe location, archeology, earthquake prediction, biomedical, manufacturing quality control, and law enforcement.

Radar

Another family, which may be solved with electro-optical methods, scatterometer radar, or a combination, is detecting wakes of surface vessels, as well as effects on the water surface caused by underwater vessels and weapons.