Pirate television

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Pirate_television 

A pirate television station is a broadcast television station that operates without a broadcast license. Like its counterpart pirate radio, the term pirate TV lacks a specific universal interpretation. It implies a form of broadcasting that is unwelcome by the licensing authorities within the territory where its signals are received, especially when the country of transmission is the same as the country of reception. When the area of transmission is not a country, or when it is a country and the transmissions are not illegal, those same broadcast signals may be deemed illegal in the country of reception. Pirate television stations may also be known as "bootleg TV", or confused with licensed low-power broadcasting (LPTV) or amateur television (ATV) services.

History

The apparently first pirate TV station in the US was Lanesville TV, active between 1972-1977 and operated by the counter-cultural video collective the Videofreex from Lanesville, New York. Another documented pirate TV station in the 1970s was Lucky 7, which broadcast for a single weekend in April 1978 from Syracuse, New York.

Techniques

There are several techniques for pirate TV broadcasting, most of which have been made very difficult, or obsolete, by better security measures and the move to digital television.

Relay hijack (analogue)

Many analogue relay transmitters would "listen" to a more powerful main transmitter and relay the signal verbatim. If the main transmitter ceases broadcasting (for example, if a station closes down overnight) then a pirate signal on the same frequency as the main transmitter could cause the relay to "wake up" and relay unauthorized programming instead. Typically this would be done by outputting a very weak RF signal within the immediate vicinity of the relay: for example, a video cassette recorder (such as a 12v system designed for use in trucks) sending its signal to a home-made antenna pointed at the relay. As the pirate signal is relatively weak, the source can be difficult to locate if it is well hidden.

A significant benefit of this attack is that the potential viewers do not have to re-tune their televisions to view the content. The content simply appears on an existing channel, after close-down.

This attack is generally now prevented by the channels broadcasting 24 hours per day (e.g. showing test cards instead of closing down), by using satellite feeds instead of repeating terrestrial signals, by electronic security to lock the relay to the authorised source, or by the switch to digital television.

Unsecured analogue satellite transponders have also been reported to have been hijacked in a similar manner.

Source hijack (analogue or digital)

In this scenario, a man-in-the-middle attack is performed upon the source material, such that authorized official transmissions are fed with unauthorized programming from the central studio or play-out facility. For example, a link feed (e.g. outside broadcast) is hijacked by a stronger pirate signal, or pre-recorded media (such as videotapes or hard drives) are swapped over for unauthorised content. This attack would generally have to be performed by an insider or by gaining access to studio facilities by social engineering.

Unauthorized transmitter (analogue)

As with most pirate radio stations, reasonably powerful VHF/UHF transmitters can be built relatively easily by any sufficiently experienced electronics hobbyist, or imported from a less strict country. The primary challenge to this technique is finding a suitable yet inconspicuous vantage point for the transmission antenna, and the risk of getting caught. If the pirate signal is strong enough to be received directly, it will also be strong enough to be tracked down.

Unauthorized multiplex (digital)

The advent of digital television makes pirate television broadcasting more difficult. Channels are broadcast as part of a multiplex that carries several channels in one signal, and it is almost impossible to insert an unauthorized channel into an authorized multiplex, or to re-activate an off-air channel. In order to broadcast an unauthorized digital TV channel, not only must the perpetrator build or obtain a VHF/UHF transmitter, they must also build or obtain, and configure, the equipment and software to digitally encode the signal and then create a stand-alone multiplex to carry it.

In Spain, in major provincial capital cities, usually operates one or more than one pirate TV digital multiplex. Some multiplexes started to operate after digital switch-over migrating pirate channels from analogue pirate television to DVB-T digital multiplexes.

Since shortly after digital switch-over and still today in secondary cities, some channels broadcast by means of a DVB-T transmitter with four analog input sources (in this case, four tuned satellite receivers connected by composite video cable) and then to amplifier, and digital signal is feed to antenna or tower. This method is the one used by most pirate TV channels. However, over the years and due to economic returns, some have begun broadcasting almost professionally. New equipment that they have been installing since three years ago allows remultiplexing of DVB-S programs into DVB-T multiplexes and most parameters can be configured at will.

Since 2010, its number has been increasing in Madrid and in Valencia, for example, and, as of March 2016, there are more than ten DVB-T pirate multiplex in Madrid metropolitan area transmitting without authorization with programming ranging from divinatory, esoteric and occult tarot or fundamentalist Christian to community television (which isn't regulated in Spain as of 2016).

In other countries, there are reports of pirate TV digital multiplexes, but they are very rare and usually suspected to have been false reports, mistaking overspill from authorized multiplexes in neighboring regions or nearby foreign countries. Viewing numbers may be much smaller than analogue pirate TV since re-tuning a digital television may be an entirely automated process which may ignore unauthorized multiplexes, or place such channels in an obscure section of the electronic program guide.

Stations

Known stations

• beoutQ - Saudi Arabia. Started broadcasting after Qatar-based programs like beIN Sports were banned following the Qatar diplomatic crisis. Primarily airs sports programs.
• Channel D - Dublin, Ireland (c. 1981)
• iStreetTV! - Palmers Cross, Jamaica, a project of !Mediengruppe Bitnik (2008) 
• Kanal X - Leipzig, Germany. Operated during the final days of the German Democratic Republic (East Germany).
• Lanesville TV - Lanesville, New York, United States. Operated on VHF channel 3 by the video collective Videofreex and broadcast on Saturdays from 1972 to 1977 (a total of 258 broadcasts). The collective and its station is detailed in Parry D. Teasdale's book Videofreex: America's First Pirate TV Station & the Catskills Collective That Turned It On.
• Lucky 7 - Syracuse, New York, United States. Operated during the evenings of April 14–16, 1978 on VHF channel 7
• NeTWork 21 - London, England - Broadcast for around 30 minutes on Friday evenings in 1986
• New Stations Broadcasting Network - New York City, New York, United States. Intermittent series of broadcasts in Brooklyn, New York beginning in 2007 created by artist James Case Leal. In New York operates on UHF channel 17, but is also responsible for television programming in other cities including Havana, Cuba (April 20, 2009 - May 22, 2009 Ch. 16), Minneapolis, Minnesota during the RNC 2008 (Ch. 15), and Piedras Negras, Mexico (July 2008 Ch. 23).
• Northern Access Network - Canada, various locations in the late 1970s
• Nova TV - Dublin, Ireland (c. 1985)
• Odelia TV - Operated briefly in 1981 on UHF channel 58, offshore of Israel
• Pirate Cat TV - Operated on VHF channel 13 by Pirate Cat Radio of San Francisco, California, United States
• Star Ray TV - Broadcasting on UHF channel 15 in the Beaches neighborhood of Toronto, Ontario, Canada
• Telstar TV (c. 1984) Birmingham, United Kingdom. Broadcast for about eight weeks on the BBC2 transmitter in the Northfield and Rubery areas of Birmingham. Showed a mixture of films and pop videos after BBC2 closed at weekends and went unnoticed by the authorities for several weeks, much to their embarrassment
• Telestreet - Italy - Movement that set up pirate TV micro-stations
• Thameside TV - London, England - A very early pirate TV station set up by Thameside Radio. There were only two known broadcasts in December 1987.
• TV Noordzee - A 1964 TV station on VHF channel 11 which, along with Radio Noordzee (not to be confused with the later Radio North Sea International), broadcast from "REM Island", an artificial platform 6 miles offshore of Noordwijk in the Netherlands. Both of the stations were knocked off the air by a sea and air raid by the armed forces of the Netherlands.
• TV Randers Syd - Randers, Denmark. Operated during 1981 and 1982. It was mostly broadcasting TV shows with music and entertainment recorded from German and Swedish TV channels and American movies. After two years of broadcasting the pirate was found in the suburb of Vorup and the station was closed by the authorities.
• TV Syd - A short-lived offshore TV station that broadcast on UHF channel 41. It was the sister station of Radio Syd and broadcast from the MV Cheeta 2 anchored off the Swedish coast.
• Voice of Nuclear Disarmament - Operating in the 1960s and technically a radio station, it broadcast pre-recorded programs from high-rise rooftops in the Greater London area on the audio portion of BBC1's television frequency after the station signed off for the night. Programming consisted of interviews, announcements, folk songs, and field recordings.
• WGUN - Mentioned in an article by Shannon Huniwell in Popular Communications magazine, this was a short-lived pirate station in the Lynchburg, Virginia area that broadcast on channel 45 during the late 1970s. The sole broadcast consisted of a water pistol with "WGUN 45 TV" in cut out letters mounted on a phonograph turntable with audio from "an unmercifully scratchy Baja Marimba Band album". The station was located by radio station technicians after being informed by the mother of a young viewer who found the station while tuning the UHF TV band. When asked, the young unnamed pirate stated he purchased the transmitter, an EMC Model TXRU-100 UHF transmitter, at a rummage sale from a church that had intended to start a UHF-TV station. Upon being informed that his broadcasts were illegal, the station was shut down. The transmitter was reportedly re-sold at a yard sale.
• W10BM - Morehead, Kentucky, United States - Originally a licensed LPTV station on VHF channel 10, it operated from 1998 to 2019 on a canceled license, making it a pirate broadcaster.

During the 1980s, large numbers of pirate TV stations operated in Italy, Greece, Spain and Israel. Subsequent legislation lead to the licensing of many of these stations and the closure of (most of) the remainder.

Proposed stations

• Caroline TV - Advertised in 1970, this was to have been a project related to Radio Caroline, which at the time was off the air. Artwork showing the proposed station's identification graphics were released, but the station, which was to be broadcast from an airplane (similar to Stratovision), never materialized, although there are two website domains, called www.carolinetv.co.uk. And carolinetelevision.com
• City TV - Was to have broadcast from a decommissioned minesweeper offshore of England. Plans for the station were announced on 8 June 1965, and was to have broadcast on VHF channel 3, but the station never materialized. It is not to be confused with the later CityTV in Toronto and Vancouver, Canada, which began operation in 1972 and are fully licensed and legal full-power stations.
• Sealand Television - Was to have broadcast on Channel 28 from the Principality of Sealand, a micronation established on a World War Two gunnery platform off the coast of Essex, England. The station, which was announced to start in September 1987, was to have been financed by Wallace Kemper, who was facing fraud and conspiracy charges.
• Tower TV - Was to have broadcast from Sunk Head Fort, 14 miles offshore of Essex, England. Reportedly held a test transmission at 4:20 AM on Tuesday 9 November 1965. If this station had gone on air it would have probably caused interference with a legitimate transmitter at Peterborough on the same frequency.

Pirate television in popular culture

Movies

Movies often show Pirate TV channels simply "breaking in" over the top of existing channels, often all of them simultaneously.

• The American Way (1986) (also known as Riders of the Storm) - Disgruntled Vietnam War veterans operate S&M TV, a pirate TV station, from an airborne B-29 airplane.
• Band Waggon (1940) - British film about a pair of out-of-work performers who are evicted from squatting on the roof of Broadcasting House (where BBC's studios were located). After moving into a supposedly haunted castle, they discover television transmission equipment used by German secret agents and use it to put on a show on the BBC's frequencies.
• Batman (1989) - The Joker overpowers a TV signal to broadcast a commercial for his deadly "Smilex", a gimmick in keeping with his comics counterpart.
• Bedwin Hacker (2003) - A Tunisian woman hijacks TV signals as a form of political protest, broadcasting short text messages with pictures of a cartoon Camel. A French counter-intelligence (DST) computer expert attempts to track her down by way of a spy sent to infiltrate the hacker's social circle. Note this was several years before the Arab Spring.
• Death Race 2000 (1975) - Political revolutionaries use broadcast signal intrusion to announce their plans to sabotage a transcontinental road race.
• District 13 (2004) - The protagonists force a Defense Secretary into admitting he was planning to detonate a neutron bomb, and the videotaped confession is broadcast via pirate transmission.
• Free Amerika Broadcasting (1981) - During a state of political upheaval in the USA, a group of rebels in Michigan set up a pirate television station.
• Hackers (1995) - One of the characters, Dade "Zero Cool" Murphy, hacks into a TV station's network feed and switches the programming to an episode of The Outer Limits. A fictional TV show, Hack the Planet, is shown on a pirate TV channel.
• Iron Man 3 (2013) - Crippled scientist Aldrich Killian covers up his illegal Extremis failures, which are 3000 °C explosions, by using broadcast signal intrusion to broadcast terrorist threats, which are performed by actor Trevor Slattery under the alias The Mandarin.
• The Pink Panther Strikes Again (1976) - Charles Dreyfus uses a broadcast intrusion to deliver his ultimatum to the world: kill Jacques Clouseau or be annihilated by laser.
• RoboCop 3 (1993) - Dr. Lazarus and Nikko transmit over Mediabreak to tell the city about the goings-on in Cadillac Heights.
• The Running Man (1987) - Revolutionaries use broadcast signal intrusion to "detour" a popular TV game show.
• Serenity (2005) - Criminals with a sense of honor use a pirate television broadcast to expose a large governmental cover-up.
• Simon (1980) - A psychology professor, brainwashed by scientists as a prank to believe he is of extraterrestrial origin, attempts to reform American society by broadcasting his pronouncements with a high-power transmitter that overrides TV network feeds, becoming a national celebrity in the process.
• They Live (1988) - A group, seeking to warn the populace of an alien invasion, use broadcast signal intrusion on local TV programming.
• Used Cars (1980) - Feuding used car lot owners use broadcast signal intrusion to discredit each other.
• V for Vendetta (2005) - The main character, a revolutionary named "V", hacks into the TV, broadcasting his plans all over Britain. The film has influenced many in real life to do the same.
• Videodrome (1983) - A TV technician discovers an encrypted pirate TV signal transmitting what appear to be snuff films.

Television

• Al TV (1980s–90s) - Series of MTV specials hosted by "Weird Al" Yankovic, using his own pirate transmitter to take over MTV's signal to play unusual music videos and comedy bits.
• Batman (1966–68) - In the episode "The Minstrel's Shakedown", the titular villain uses a broadcast signal intrusion to threaten the police and the stock exchange of Gotham City.
• Channel Umptee-3 (1997) - Animated children's educational television series. The main characters operate a pirate TV station "located in the white space between channels".
• Club Mario (1990–91) - A repackaged version of The Super Mario Bros. Super Show!. The new wrap-around segments had the hosts hijacking a TV signal to broadcast video of their antics, the Super Mario Bros. and Legend of Zelda cartoon shorts used in Super Show!, and redubbed clips from the short-lived Photon TV series.
• Feral TV (1995–97) - Australian children's comedy television series. The main characters find an underground cable TV feed and use it to broadcast a pirate TV station.
• Disney Club (Brazil) (1997–2002) - in the Brazilian version, later renamed to Disney CRUJ, the protagonists operate a pirate TV station.
• Dark Angel (2000–2002) - One of the series protagonists, Logan Cale, operated a pirate television broadcast known as "Eyes Only" primarily to broadcast news reports, expose political/corporate corruption, issue public alerts, etc.
• Ed, Edd N Eddy (1999–2009) - In the episode "A Town Called Ed", the Eds use a pirate TV transmitter to inform the neighborhood kids of Eddy’s roots as a founding father.
• Family Guy - On the episode "PTV", Peter Griffin, angered that authorities are censoring TV broadcasts, starts his own well-liked pirate TV station, PTV, containing deleted risqué scenes from movies and TV shows, partial nudity from TV programs and dogs mating.
• Green Acres - In the episode "How to Succeed In Television Without Really Trying", a Hooterville whiz-kid builds a pirate TV station in Mr. Douglass' barn. Mr. Douglass gets undressed in the barn, not knowing that he is now starring on TV in Hooterville. The FCC drops in to shut Mr. Douglass down, and he tries to deny the whole thing, but at the same time, Mr. Haney drives up with a rack full of men's underwear. He tells Mr. Douglass that he needs some new shorts for his next undressing show.
• Max Headroom (1987) - One of the TV series' characters, "Blank Reg", runs Big Time Television, a pirate station, from a converted bus.
• Rock 'N' America was a 1984 US series in which Rick Ducommun played a VJ named Rick, who would play rock videos by "jamming into" existing TV channels. The character was relentlessly, but always unsuccessfully, pursued by an FCC agent. When the agent asked if Rick was doing it for a lark, Rick replied (via his illegal transmission) that his father had invented the system and offered it to the US military for jamming into Nazi propaganda broadcasts during World War II, but had been rebuffed.
• The Simpsons - In the episode "Sideshow Bob's Last Gleaming", Springfield is ordered by Sideshow Bob to shut down all its television stations or face nuclear devastation. Krusty the Clown refuses to comply with the demands and uses an abandoned Emergency Broadcast System transmitter to operate a pirate TV station and broadcast heavily improvised material.
• Torchwood (2006–11) - In "Children of Earth: Day Five," a pirate television station broadcasts footage of soldiers taking children to a rendezvous point on "Digital 141."

Music

• Flaunt It (1986) - The debut album by British band Sigue Sigue Sputnik was notable for containing paid advertisements between the tracks and in the liner notes, including one for London pirate TV station NeTWork 21.

Books

• The Moon Is a Harsh Mistress (1966) - In this science fiction novel, a self-aware computer helps revolutionaries by generating and broadcasting synthesized TV transmissions of their non-existent leader "Adam Selene" via an internal TV network.
• Mockingjay (2010) - This book, the third in The Hunger Games trilogy, describes the hacking of official government television broadcasts at several points in the novel, replacing them with calls to revolution, before the original broadcasts are restored by the government.

Comic books

• Batman villain the Joker often announces his crimes to Gotham City this way, in keeping with his theme as a showman. In the character's earliest appearances (including his debut in Batman #1 from the spring of 1940), he used radio broadcasts to this effect.
• American Flagg! (1983–1989) - A science fiction comic book series created by Howard Chaykin set in the early 2030s. A plot device in the story is Q-USA, a pirate TV station that broadcasts illegal sports, pornography, and movies and television shows made before the collapse of the pre-existing order .
• WRAB: Pirate Television (1985) A graphic novel by Matt Howarth and part of his Post Brothers story arc. An off-shore pirate television station operating in international waters interrupts satellite broadcasts with the intention of gaining a global audience.

Whale vocalization

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Whale_vocalization

Whales use a variety of sounds for communication and sensation. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, including whales, dolphins, and porpoises, are much more dependent on sound than land mammals due to the limited effectiveness of other senses in water. Sight is less effective for marine mammals because of the particulate way in which the ocean scatters light. Smell is also limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly four times greater in water than in the atmosphere at sea level. As sea mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships, sonar and marine seismic surveys.

The word "song" is used to describe the pattern of regular and predictable sounds made by some species of whales, notably the humpback whale. This is included with or in comparison with music, and male humpback whales have been described as "inveterate composers" of songs that are "'strikingly similar' to human musical traditions". It has been suggested that humpback songs communicate male fitness to female whales. The click sounds made by sperm whales and dolphins are not strictly song, but the clicking sequences have been suggested to be individualized rhythmic sequences that communicate the identity of a single whale to other whales in its group. These clicking sequences reportedly allow the groups to coordinate foraging activities.

Production of sound

Humans produce voiced sounds by passing air through the larynx. Within the larynx, when the vocal cords are brought close together, the passing air will force them to alternately close and open, separating the continuous airstream into discrete pulses of air that are heard as a vibration. This vibration is further modified by speech organs in the oral and nasal cavities, creating sounds which are used in human speech.

Cetacean sound production differs markedly from this mechanism. The precise mechanism differs in the two major suborders of cetaceans: the Odontoceti (toothed whales, including dolphins) and the Mysticeti (baleen whales, including the largest whales such as the blue whale).

Odontocete whales

Process in a dolphin echolocation: in green the sounds generated by the dolphin, in red from the fish.

 

Idealized dolphin head showing the regions involved in sound production. This image was redrawn from Cranford (2000).

Odontocetes produce rapid bursts of high-frequency clicks that are thought to be primarily for echolocation. Specialized organs in an odontocete produce collections of clicks and buzzes at frequencies from 0.2 to 150 kHz to obtain sonic information about its environment. Lower frequencies are used for distance echolocation, due to the fact that shorter wavelengths do not travel as far as longer wavelengths underwater. Higher frequencies are more effective at shorter distances, and can reveal more detailed information about a target. Echoes from clicks convey not only the distance to the target, but also the size, shape, speed, and vector of its movement. Additionally, echolocation allows the odontocete to easily discern the difference between objects that are different in material composition, even if visually identical, by their different densities. Individuals also appear to be able to isolate their own echoes during pod feeding activity without interference from other pod members' echolocations.

Whistles are used for communication, and four- to six-month-old calves develop unique sounds that they use most frequently throughout their lives. Such "signature whistles" are distinctive to the individual and may serve as a form of identification among other odontocetes. Though a large pod of dolphins will produce a wide range of different noises, very little is known about the meaning of the sound. Frankel quotes one researcher who says listening to a school of odontocetes is like listening to a group of children at a school playground.

The multiple sounds odontocetes make are produced by passing air through a structure in the head called the phonic lips. The structure is analogous to the human nasal cavity, but the phonic lips act similarly to human vocal cords, which in humans are located in the larynx. As the air passes through this narrow passage, the phonic lip membranes are sucked together, causing the surrounding tissue to vibrate. These vibrations can, as with the vibrations in the human larynx, be consciously controlled with great sensitivity. The vibrations pass through the tissue of the head to the melon, which shapes and directs the sound into a beam of sound useful in echolocation. Every toothed whale except the sperm whale has two sets of phonic lips and is thus capable of making two sounds independently. Once the air has passed the phonic lips it enters the vestibular sac. From there, the air may be recycled back into the lower part of the nasal complex, ready to be used for sound creation again, or passed out through the blowhole.

The French name for phonic lips, museau de singe, translates literally as "monkey's muzzle", which the phonic lip structure is supposed to resemble. New cranial analysis using computed axial and single photon emission computed tomography scans in 2004 showed, at least in the case of bottlenose dolphins, that air might be supplied to the nasal complex from the lungs by the palatopharyngeal sphincter, enabling the sound creation process to continue for as long as the dolphin is able to hold its breath.

Mysticete whales

Baleen whales (formally called mysticetes) do not have phonic lip structure. Instead, they have a larynx that appears to play a role in sound production, but it lacks vocal cords, and scientists remain uncertain as to the exact mechanism. The process, however, cannot be completely analogous to humans, because whales do not have to exhale in order to produce sound. It is likely that they recycle air around the body for this purpose. Cranial sinuses may also be used to create the sounds, but again, researchers are currently unsure how.

Vocal plasticity and acoustic behavior

There are at least nine separate blue whale acoustic populations worldwide. Over the last 50 years blue whales have changed the way they are singing. Calls are progressively getting lower in frequency. For example, the Australian pygmy blue whales are decreasing their mean call frequency rate at approximately 0.35 Hz/year.

The migration patterns of blue whales remains unclear. Some populations appear to be resident in habitats of year-round high productivity in some years, while others undertake long migrations to high-latitude feeding grounds, but the extent of migrations and the components of the populations that undertake them are poorly known.

Sound levels

The frequency of baleen whale sounds ranges from 10 Hz to 31 kHz. A list of typical levels is shown in the table below.

Source	Broadband source level (dB re 1 ${\displaystyle \mu }$Pa at 1m)
Fin whale moans	155–186
Blue whale moans	155–188
Gray whale moans	142–185
Bowhead whale tonals, moans and song	128–189

Purpose of whale-created sounds

While the complex sounds of the humpback whale (and some blue whales) are believed to be primarily used in sexual selection, there are simpler sounds that are created by other species of whales that have an alternative use and are used all year round. Whale watchers have watched mother whales lift their young towards the surface in a playful motion, while making a noise that resembles cooing in humans. This cooing-like noise made by whales seems designed to relax their young and is one of several distinct everyday noises whales are known to make. Unlike some fish such as sharks and dolphins, a toothed whale's sense of smell is absent, causing them to rely heavily on echolocation, both for hunting prey and for navigating the ocean under darkness. This requires the whales to produce noise year round to ensure they are able to navigate around any obstacles they may face such as sunken ships or other animals.

It has also been proven that whales are extremely social creatures. The noises that are made throughout the entire year (the main sounds being whistles, clicks, and pulsed calls) are used to communicate with other members of their pod. Each sound a whale makes could mean something different. The clicking noises whales make are used for navigation.   

The question of whether whales sometimes sing purely for aesthetic enjoyment, personal satisfaction, or 'for art's sake', is considered by some to be "an untestable question".

Song of the humpback whale

Two groups of whales, the humpback whale and the subspecies of blue whale found in the Indian Ocean, are known to produce a series of repetitious sounds at varying frequencies known as whale song. Marine biologist Philip Clapham describes the song as "probably the most complex in the animal kingdom."

Male humpback whales perform these vocalizations often during the mating season, and so it is believed the purpose of songs is to aid mate selection.

Interest in whale song was aroused by researchers Roger Payne and Scott McVay after the songs were brought to their attention by a Bermudian named Frank Watlington who was working for the US government at the SOFAR station listening for Russian submarines with underwater hydrophones off the coast of the island. Payne released the best-selling Songs of the Humpback Whale in 1970, and the whale songs were quickly incorporated into human music by, among others, singer Judy Collins.

The songs follow a distinct hierarchical structure. The base units of the song (sometimes loosely called the "notes") are single uninterrupted emissions of sound that last up to a few seconds. These sounds vary in frequency from 20 Hz to upward of 24 kHz (the typical human range of hearing is 20 Hz to 20 kHz). The units may be frequency modulated (i.e., the pitch of the sound may go up, down, or stay the same during the note) or amplitude modulated (get louder or quieter). However, the adjustment of bandwidth on a spectrogram representation of the song reveals the essentially pulsed nature of the FM sounds.

A collection of four or six units is known as a sub-phrase, lasting perhaps ten seconds (see also phrase (music)). A collection of two sub-phrases is a phrase. A whale will typically repeat the same phrase over and over for two to four minutes. This is known as a theme. A collection of themes is known as a song. The whale song will last up to 30 or so minutes, and will be repeated over and over again over the course of hours or even days. This "Russian doll" hierarchy of sounds suggests a syntactic structure that is more human-like in its complexity than other forms of animal communication like bird songs, which have only linear structure.

All the whales in an area sing virtually the same song at any point in time and the song is constantly and slowly evolving over time. For example, over the course of a month a particular unit that started as an upsweep (increasing in frequency) might slowly flatten to become a constant note. Another unit may get steadily louder. The pace of evolution of a whale's song also changes—some years the song may change quite rapidly, whereas in other years little variation may be recorded.

Idealized schematic of the song of a humpback whale.
Redrawn from Payne, et al. (1983)

 

Humpback whale, sound spectrum and time plots

Whales occupying the same geographical areas (which can be as large as entire ocean basins) tend to sing similar songs, with only slight variations. Whales from non-overlapping regions sing entirely different songs.

As the song evolves, it appears that old patterns are not revisited. An analysis of 19 years of whale songs found that while general patterns in song could be spotted, the same combination never recurred.

Humpback whales may also make stand-alone sounds that do not form part of a song, particularly during courtship rituals. Finally, humpbacks make a third class of sound called the feeding call. This is a long sound (5 to 10 s duration) of near constant frequency. Humpbacks generally feed cooperatively by gathering in groups, swimming underneath shoals of fish and all lunging up vertically through the fish and out of the water together. Prior to these lunges, whales make their feeding call. The exact purpose of the call is not known.

Some scientists have proposed that humpback whale songs may serve an echolocative purpose, but this has been subject to disagreement.

Other whale sounds

Humpback whales have also been found to make a range of other social sounds to communicate such as "grunts", "groans", "thwops", "snorts" and "barks".

In 2009, researchers found that blue whale song has been deepening in its tonal frequency since the 1960s. While noise pollution has increased ambient ocean noise by over 12 decibels since the mid-20th century, researcher Mark McDonald indicated that higher pitches would be expected if the whales were straining to be heard.

Killer whales have been observed to produce long range calls that are stereotyped and high frequency travelling distances from 10–16 km (6.2–9.9 mi) as well as short range calls that can travel distances from 5–9 km (3.1–5.6 mi). Short range calls are reported during social and resting periods while long range are more commonly reported during foraging and feeding.

Most other whales and dolphins produce sounds of varying degrees of complexity. Of particular interest is the Beluga (the "sea canary") which produces an immense variety of whistles, clicks and pulses.

Research in Whale Vocalization

It was previously thought that most baleen whales make sounds at about 15–20 hertz. However, a team of marine biologists, led by Mary Ann Daher of the Woods Hole Oceanographic Institution, reported in New Scientist in December 2004 that they had been tracking a whale in the North Pacific for 12 years that was "singing" at 52 Hz. Scientists have been unable to explain this phenomenon. 52 Hz is a very low sound, it is audible through human ears as a low moaning sound. It was not expected that this whale was a new species, more so this whale indicated that a currently known species potentially has a much wider vocal range than previously thought. There is disagreement in the scientific community regarding the uniqueness of the whale's vocalization and whether it is a member of a hybrid whale such as the well documented blue and fin whale hybrids.

Human interaction

Blue whales stop producing foraging D calls once a mid-frequency sonar is activated, even though the sonar frequency range (1–8 kHz) far exceeds their sound production range (25–100 Hz).

 

Voyager Golden Records carried whale songs into outer space with other sounds representing planet Earth.

Researchers use hydrophones (often adapted from their original military use in tracking submarines) to ascertain the exact location of the origin of whale noises. Their methods also allow them to detect how far through an ocean a sound travels. Research by Dr. Christopher Clark of Cornell University conducted using military data showed that whale noises travel for thousands of kilometres. As well as providing information about song production, the data allows researchers to follow the migratory path of whales throughout the "singing" (mating) season. An important finding is that whales, in a process called the Lombard effect, adjust their song to compensate for background noise pollution. Moreover, there is evidence that blue whales stop producing foraging D calls once a mid-frequency sonar is activated, even though the sonar frequency range (1–8 kHz) far exceeds their sound production range (25–100 Hz).

Prior to the introduction of human noise production, Clark says the noises may have travelled right from one side of an ocean to the other, agreeing with a thirty-year-old concept blaming large-scale shipping. His research indicates that ambient noise from boats is doubling with each decade. This has the effect of reducing the range at which whale noises can be heard. Environmentalists fear that such boat activity is putting undue stress on the animals as well as making it difficult to find a mate.

In the past decade, many effective automated methods, such as signal processing, data mining, and machine learning techniques have been developed to detect and classify whale vocalizations.

Media

See also: List of whale vocalizations

 

A humpback whale song

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Common humpback whale vocalizations on a windy day

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An orca's song

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An orca's song, at a distance

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Vocalizations of an orca

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A fin whale song

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A blue whale song

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Recorded in the Atlantic (1)

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A blue whale song

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Recorded in the Atlantic (2)

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A blue whale song

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Recorded in North Eastern Pacific

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A blue whale song

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Recorded in the South Pacific

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A blue whale song

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Recorded in the West Pacific

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An Atlantic minke whale

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Selected discography

• Songs of the Humpback Whale (SWR 118) was originally released in 1970 by CRM Records from recordings made by Roger Payne, Frank Watlington, and others. The LP was later re-released by Capitol Records, published in a flexible format in the National Geographic Society magazine, Volume 155, Number 1, in January 1979, re-released by Living Music/Windham Hill/BMG Records on CD in 1992, and remastered on CD by BGO-Beat Goes On in 2001.
• Deep Voices: The Second Whale Record (Capitol/EMI Records 0777 7 11598 1 0) was released on LP in 1977 from additional recordings made by Roger Payne, and re-released on CD in 1995 by Living Music/Windham Hill/BMG Records. It includes recordings of humpbacks, blues, and rights.
• Northern Whales (MGE 19) was released by Music Gallery Editions from recordings made by Pierre Ouellet, John Ford, and others affiliated with Interspecies Music and Communication Research. It includes recordings of belugas, narwhals, orca, and bearded seals.
• Sounds of the Earth: Humpback Whales (Oreade Music) was released on CD in 1999.
• Rapture of the Deep: Humpback Whale Singing (Compass Recordings) was released on CD in 2001.
• Songlines: Songs of the East Australian Humpback whales. was released in 2009.

History

Whaling Captain Wm. H. Kelly was the first person known to recognize whale singing for what it was, while on the brig Eliza in the Sea of Japan in 1881.

 

Hall-effect thruster

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hall-effect_thruster 

 

6 kW Hall thruster in operation at the NASA Jet Propulsion Laboratory

In spacecraft propulsion, a Hall-effect thruster (HET) is a type of ion thruster in which the propellant is accelerated by an electric field. Hall-effect thrusters (based on the discovery by Edwin Hall) are sometimes referred to as Hall thrusters or Hall-current thrusters. Hall-effect thrusters use a magnetic field to limit the electrons' axial motion and then use them to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the ions in the plume. The Hall-effect thruster is classed as a moderate specific impulse (1,600 s) space propulsion technology and has benefited from considerable theoretical and experimental research since the 1960s.

Hall thrusters operate on a variety of propellants, the most common being xenon and krypton. Other propellants of interest include argon, bismuth, iodine, magnesium, zinc and adamantane.

Hall thrusters are able to accelerate their exhaust to speeds between 10 and 80 km/s (1,000–8,000 s specific impulse), with most models operating between 15 and 30 km/s. The thrust produced depends on the power level. Devices operating at 1.35 kW produce about 83 mN of thrust. High-power models have demonstrated up to 5.4 N in the laboratory. Power levels up to 100 kW have been demonstrated for xenon Hall thrusters.

As of 2009, Hall-effect thrusters ranged in input power levels from 1.35 to 10 kilowatts and had exhaust velocities of 10–50 kilometers per second, with thrust of 40–600 millinewtons and efficiency in the range of 45–60 percent. The applications of Hall-effect thrusters include control of the orientation and position of orbiting satellites and use as a main propulsion engine for medium-size robotic space vehicles.

History

Hall thrusters were studied independently in the United States and the Soviet Union. They were first described publicly in the US in the early 1960s. However, the Hall thruster was first developed into an efficient propulsion device in the Soviet Union. In the US, scientists focused on developing gridded ion thrusters.

Two types of Hall thrusters were developed in the Soviet Union:

• thrusters with wide acceleration zone, SPT (Russian: СПД, стационарный плазменный двигатель; English: SPT, Stationary Plasma Thruster) at Design Bureau Fakel
• thrusters with narrow acceleration zone, DAS (Russian: ДАС, двигатель с анодным слоем; English: TAL, Thruster with Anode Layer), at the Central Research Institute for Machine Building (TsNIIMASH).

Soviet and Russian SPT thrusters

The SPT design was largely the work of A. I. Morozov. The first SPT to operate in space, an SPT-50 aboard a Soviet Meteor spacecraft, was launched December 1971. They were mainly used for satellite stabilization in north–south and in east–west directions. Since then until the late 1990s 118 SPT engines completed their mission and some 50 continued to be operated. Thrust of the first generation of SPT engines, SPT-50 and SPT-60 was 20 and 30 mN respectively. In 1982, SPT-70 and SPT-100 were introduced, their thrusts being 40 and 83 mN, respectively. In the post-Soviet Russia high-power (a few kilowatts) SPT-140, SPT-160, SPT-200, T-160 and low-power (less than 500 W) SPT-35 were introduced.

Soviet and Russian TAL-type thrusters include the D-38, D-55, D-80, and D-100.

Soviet-built thrusters were introduced to the West in 1992 after a team of electric propulsion specialists from NASA's Jet Propulsion Laboratory, Glenn Research Center, and the Air Force Research Laboratory, under the support of the Ballistic Missile Defense Organization, visited Russian laboratories and experimentally evaluated the SPT-100 (i.e., a 100 mm diameter SPT thruster). Over 200 Hall thrusters have been flown on Soviet/Russian satellites in the past thirty years. No failures have ever occurred on orbit. Hall thrusters continue to be used on Russian spacecraft and have also flown on European and American spacecraft. Space Systems/Loral, an American commercial satellite manufacturer, now flies Fakel SPT-100's on their GEO communications spacecraft.

Since their introduction to the West in the early 1990s, Hall thrusters have been the subject of a large number of research efforts throughout the United States, France, Italy, Japan, and Russia (with many smaller efforts scattered in various countries across the globe). Hall thruster research in the US is conducted at several government laboratories, universities and private companies. Government and government funded centers include NASA's Jet Propulsion Laboratory, NASA's Glenn Research Center, the Air Force Research Laboratory (Edwards AFB, CA), and The Aerospace Corporation. Universities include the US Air Force Institute of Technology, University of Michigan, Stanford University, The Massachusetts Institute of Technology, Princeton University, Michigan Technological University, and Georgia Tech. A considerable amount of development is being conducted in industry, such as IHI Corporation in Japan, Aerojet and Busek in the US, SNECMA in France, LAJP in Ukraine, SITAEL in Italy, and Satrec Initiative in South Korea.

The first use of Hall thrusters on lunar orbit was the European Space Agency (ESA) lunar mission SMART-1 in 2003.

Hall thrusters were first demonstrated on a western satellite on the Naval Research Laboratory (NRL) STEX spacecraft, which flew the Russian D-55. The first American Hall thruster to fly in space was the Busek BHT-200 on TacSat-2 technology demonstration spacecraft. The first flight of an American Hall thruster on an operational mission, was the Aerojet BPT-4000, which launched August 2010 on the military Advanced Extremely High Frequency GEO communications satellite. At 4.5 kW, the BPT-4000 is also the highest power Hall thruster ever flown in space. Besides the usual stationkeeping tasks, the BPT-4000 is also providing orbit raising capability to the spacecraft. The X-37B has been used as a testbed for the Hall thruster for the AEHF satellite series. Several countries worldwide continue efforts to qualify Hall thruster technology for commercial uses. The SpaceX Starlink constellation, the largest satellite constellation in the world, uses Hall thrusters. They are also included in the design of the Psyche spacecraft for asteroid exploration.

Principle of operation

The essential working principle of the Hall thruster is that it uses an electrostatic potential to accelerate ions up to high speeds. In a Hall thruster, the attractive negative charge is provided by an electron plasma at the open end of the thruster instead of a grid. A radial magnetic field of about 100–300 G (0.01–0.03 T) is used to confine the electrons, where the combination of the radial magnetic field and axial electric field cause the electrons to drift in azimuth thus forming the Hall current from which the device gets its name.

Hall thruster. Hall thrusters are largely axially symmetric. This is a cross-section containing that axis.

A schematic of a Hall thruster is shown in the adjacent image. An electric potential of between 150 and 800 volts is applied between the anode and cathode.

The central spike forms one pole of an electromagnet and is surrounded by an annular space, and around that is the other pole of the electromagnet, with a radial magnetic field in between.

The propellant, such as xenon gas, is fed through the anode, which has numerous small holes in it to act as a gas distributor. As the neutral xenon atoms diffuse into the channel of the thruster, they are ionized by collisions with circulating high-energy electrons (typically 10–40 eV, or about 10% of the discharge voltage). Most of the xenon atoms are ionized to a net charge of +1, but a noticeable fraction (~20%) have +2 net charge.

The xenon ions are then accelerated by the electric field between the anode and the cathode. For discharge voltages of 300 V, the ions reach speeds of around 15 km/s (9.3 mps) for a specific impulse of 1,500 seconds (15 kN·s/kg). Upon exiting, however, the ions pull an equal number of electrons with them, creating a plasma plume with no net charge.

The radial magnetic field is designed to be strong enough to substantially deflect the low-mass electrons, but not the high-mass ions, which have a much larger gyroradius and are hardly impeded. The majority of electrons are thus stuck orbiting in the region of high radial magnetic field near the thruster exit plane, trapped in E×B (axial electric field and radial magnetic field). This orbital rotation of the electrons is a circulating Hall current, and it is from this that the Hall thruster gets its name. Collisions with other particles and walls, as well as plasma instabilities, allow some of the electrons to be freed from the magnetic field, and they drift towards the anode.

About 20–30% of the discharge current is an electron current, which does not produce thrust, thus limiting the energetic efficiency of the thruster; the other 70–80% of the current is in the ions. Because the majority of electrons are trapped in the Hall current, they have a long residence time inside the thruster and are able to ionize almost all of the xenon propellant, allowing mass use of 90–99%. The mass use efficiency of the thruster is thus around 90%, while the discharge current efficiency is around 70%, for a combined thruster efficiency of around 63% (= 90% × 70%). Modern Hall thrusters have achieved efficiencies as high as 75% through advanced designs.

Compared to chemical rockets, the thrust is very small, on the order of 83 mN for a typical thruster operating at 300 V and 1.5 kW. For comparison, the weight of a coin like the U.S. quarter or a 20-cent Euro coin is approximately 60 mN. As with all forms of electrically powered spacecraft propulsion, thrust is limited by available power, efficiency, and specific impulse.

However, Hall thrusters operate at the high specific impulses that are typical for electric propulsion. One particular advantage of Hall thrusters, as compared to a gridded ion thruster, is that the generation and acceleration of the ions takes place in a quasi-neutral plasma, so there is no Child-Langmuir charge (space charge) saturated current limitation on the thrust density. This allows much smaller thrusters compared to gridded ion thrusters.

Another advantage is that these thrusters can use a wider variety of propellants supplied to the anode, even oxygen, although something easily ionized is needed at the cathode.

Propellants

Xenon

Xenon has been the typical choice of propellant for many electric propulsion systems, including Hall thrusters. Xenon propellant is used because of its high atomic weight and low ionization potential. Xenon is relatively easy to store, and as a gas at spacecraft operating temperatures does not need to be vaporized before usage, unlike metallic propellants such as bismuth. Xenon's high atomic weight means that the ratio of energy expended for ionization per mass unit is low, leading to a more efficient thruster.

Krypton

Krypton is another choice of propellant for Hall thrusters. Xenon has an ionization potential of 12.1298 eV, while krypton has an ionization potential of 13.996 eV. This means that thrusters utilizing krypton need to expend a slightly higher energy per mole to ionize, which reduces efficiency. Additionally, krypton is a lighter ion, so the unit mass per ionization energy is further reduced compared to xenon. However, xenon can be more than ten times as expensive as krypton per kilogram, making krypton a more economical choice for building out satellite constellations like that of SpaceX's Starlink, whose Hall thrusters are fueled with krypton.

Variants

Cylindrical Hall thrusters

An Exotrail ExoMG - nano (60W) Hall Effect Thruster firing in a vacuum chamber

Although conventional (annular) Hall thrusters are efficient in the kilowatt power regime, they become inefficient when scaled to small sizes. This is due to the difficulties associated with holding the performance scaling parameters constant while decreasing the channel size and increasing the applied magnetic field strength. This led to the design of the cylindrical Hall thruster. The cylindrical Hall thruster can be more readily scaled to smaller sizes due to its nonconventional discharge-chamber geometry and associated magnetic field profile. The cylindrical Hall thruster more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster. The primary reason for cylindrical Hall thrusters is that it is difficult to achieve a regular Hall thruster that operates over a broad envelope from ~1 kW down to ~100 W while maintaining an efficiency of 45-55%.

External discharge Hall thruster

Sputtering erosion of discharge channel walls and pole pieces that protect the magnetic circuit causes failure of thruster operation. Therefore, annular and cylindrical Hall thrusters have limited lifetime. Although magnetic shielding has been shown to dramatically reduce discharge channel wall erosion, pole piece erosion is still a concern. As an alternative, an unconventional Hall thruster design called external discharge Hall thruster or external discharge plasma thruster (XPT) has been introduced. The external discharge Hall thruster does not possess any discharge channel walls or pole pieces. Plasma discharge is produced and sustained completely in the open space outside the thruster structure, and thus erosion-free operation is achieved.

Applications

An illustration of the Gateway in orbit around the Moon. The orbit of the Gateway will be maintained with Hall thrusters.

Hall thrusters have been flying in space since December 1971, when the Soviet Union launched an SPT-50 on a Meteor satellite. Over 240 thrusters have flown in space since that time, with a 100% success rate. Hall thrusters are now routinely flown on commercial LEO and GEO communications satellites, where they are used for orbital insertion and stationkeeping.

The first Hall thruster to fly on a western satellite was a Russian D-55 built by TsNIIMASH, on the NRO's STEX spacecraft, launched on October 3, 1998.

The solar electric propulsion system of the European Space Agency's SMART-1 spacecraft used a Snecma PPS-1350-G Hall thruster. SMART-1 was a technology demonstration mission that orbited the Moon. This use of the PPS-1350-G, starting on September 28, 2003, was the first use of a Hall thruster outside geosynchronous earth orbit (GEO). Like most Hall thruster propulsion systems used in commercial applications, the Hall thruster on SMART-1 could be throttled over a range of power, specific impulse, and thrust. It has a discharge power range of 0.46–1.19 kW, a specific impulse of 1,100–1,600 s and thrust of 30–70 mN.

Many small satellites of the SpaceX Starlink cluster use krypton-fueled Hall thrusters for position-keeping and deorbiting.

Tiangong space station is fitted with Hall-effect thrusters. Tianhe core module is propelled by both chemical thrusters and four ion thrusters, which are used to adjust and maintain the station's orbit. The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention". Hall-effect thrusters are created with manned mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles. A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters. According to the Chinese Academy of Sciences, the ion drive used on Tiangong has burned continuously for 8,240 hours without a glitch, indicating their suitability for the Chinese space station’s designated 15-year lifespan. This is the world's first Hall thrusters on a human-rated mission.

The Jet Propulsion Laboratory (JPL) granted exclusive commercial licensing to Apollo Fusion- led by Mike Cassidy, for its Magnetically Shielded Miniature, or MaSMi Hall thruster technology. In January 2021, Apollo Fusion announced they had secured a contract with York Space Systems for an order of its latest iteration named the "Apollo Constellation Engine".

In late 2022, the NASA mission to the asteroid Psyche will utilize xenon gas Hall Thrusters. The electricity will come from the craft's 75 square meter solar panels.

NASA's first Hall thrusters on a human-rated mission will be a combination of 6kW Hall thrusters provided by Busek and NASA Advanced Electric Propulsion System (AEPS) Hall thrusters. They will serve as the primary propulsion on Maxar's Power and Propulsion Element (PPE) for the Lunar Gateway under NASA's Artemis program. The high specific impulse of Hall thrusters will allow for efficient orbit raising and station keep for the Lunar Gateway's polar near-rectilinear halo orbit.

In development

The highest power Hall-effect thruster in development is the University of Michigan's 100 kW X3 Nested Channel Hall Thruster. The thruster is approximately 80 cm in diameter and weighs 230 kg, and has demonstrated a thrust of 5.4 N. 

Other high power thrusters include NASA's 40 kW Advanced Electric Propulsion System (AEPS), meant to propel large-scale science missions and cargo transportation in deep space.