Lecture 4: Sonar and Anti-Submarine Warfare Flashcards
What is the law of large numbers and why is it important wrt radar and sonar?
The law of large numbers constitutes that an increase in the sample size leads to a decrease in the variance and standard errors, and the convergence of the sample mean towards ten true mean. Radar and sonar essentially use this logic to identify anomalies in the area they are scanning.
The “precision revolution”
The use of the electromagnetic spectrum has led to the precision revolution in munitions. Precise munitions are radar-guided, thermal-guided, infrared guided, GPS-guided (which use geolocation provided via radio/radar uplink to satellites).
Why is air defence so important in the context of the War on Ukraine?
Due to air defence systems, Russia has been denied the opportunity to operate over Ukrainian airspace. Ukraine’s ADSs have been intercepting drones, cruise missiles, and ballistic missiles. More broadly, air defence plays a key role in providing some countries with the capacity to deny access to their proximity to adversaries. (slide 23)
The importance of submarines in modern warfare - The Big Picture
Submarines are an important component in many a country’s defence policy. The US, UK, and Australia have signed a treaty to develop nuclear-power submarines to possess the capabilities to deploy long-range firing capabilities within the Western Pacific theatre. Taiwan has invested tremendous resources and effort to develop modern submarines as a response to the growth of China (and its behaviour in the South China Sea…).
Why are submarines of critical importance?
Submarines are incredibly useful because they are stealthy. It is difficult to detect them with human sight or sensors that are very effective in the atmosphere (i.e., radar, laser, thermal, infrared, etc.), which makes them a very effective threat. Hence, they are also the perfect platform for a multitude of tasks, such as coastal defence, conventional and nuclear deterrent, and espionage missions. (slide 52)
Submarines and nuclear deterrence
Beginning in the 1950s, submarines have been fitted with ballistic missiles. Due to their stealth, they can be considered the most secure pillar of the nuclear triad and make for credible second-strike capabilities. (slide 66)
Submarines pre-WWII
Before WWII submarines were actually submersibles and very slow underwater, meaning that they could not scout the ocean for targets. They also had to reappear periodically to recharge their batteries by running their diesel engines. Submarines are much more easily detectable and, thus, vulnerable when on the surface. To limit such vulnerability during WWII, submarines would generally be submerged during the day to avoid detection, and cruise the surface at night to scout for targets. (slide 80)
What is active sonar and what is its use in submarine detection?
Active sonar works like radar, but using sound waves instead. It emits acoustic impulses and captures their return (echo) after encountering an object. When active sonar was fielded during WWII, it permitted the scanning of waters within a radios of a couple km around the source.
What is a centimetric radar?
A centrimetic radar is a radar that operates in the super high frequency (SHF) radio frequency band. It enables the detection of much smaller objects and the use of smaller antenna than is the case for older radar systems. Its compatibility with small antennae allows it to be mounted on airplanes. Centrimetric radars were used for submarine detection during WWII, which was a core incentive for the development of submarines designed to operate primarily underwater. (slide 92)
What is passive sonar?
Passive sonar are sonar receptors (e.g., microphones/hydrophones attached to the seabed) that capture sounds from their environment. Passive sonar is commonly used in anti-submarine defence, because it captures the low-frequency sound waves produced by the machinery of (older) submarine systems (e.g., during the cooling of reactors in nuclear powered models). Seeing as low-frequency sound waves can travel over long distances, particularly in the sound fixing and ranging channel (SFRC), passive sonar can be very useful in tracking submarines. (slide 99 & Take-home exam 1)
What is the GIUK Gap and how is passive sonar used in this area?
The GIUK Gap refers to the stretches of the North Atlantic Ocean that separate Greenland, Iceland, and the UK from each other. It is a naval chokepoint/bottleneck and vital for ensuring that “sea lines of communication (SLOC) and supply lines are uninterrupted between NATO’s European members and the United States.” (slides 104-106 & Wikipedia) The Sound Surveillance System (SOSUS) employed passive sonar to detect Soviet submarines around the GIUK gap amongst other places.
