Pressão atmosférica - Barómetro primitivo

Uma referência interessante acerca da necessidade de avaliar a pressão atmosférica na actividade náutica.

Ninguém duvida que após a invenção do barómetro, tal como hoje o conhecemos, a actividade náutica passou a de dispor de um instrumento de grande utilidade permitindo ao navegador saber da situação no momento da pressão atmosférica e avaliar as condições meteorológicas expectáveis.

Todos nós sabemos que uma situação de pressão atmoférica alta está associada a condições meteorológicas de bom tempo enquanto que uma pressão atmoférica de valor baixo significa uma condição de mau tempo, de tempestade.


Ora Peter Trickett no seu livro "Beyond Capricorn" a páginas 86 escreve:

»»»The forerunner of the modern barometer was not invented until 1643. Instead, Portuguese pilots in the sixteenth century employed a curious form of 'live' barometer consisting of a leech swimming in a bottle of spring water. The position of the leech in the bottle on any given day was held to predict the weather. The system was more sophisticated than it might sound. There were no fewer than nine recognised positions for the leech, and navigators memorised a set of nine rhyming verses to remind them of what each position foretold. As a rule of thumb, the finer the impending weather, the lower in water the leech would swim. Conversely, if the leech climbed high in the bottle it would be a warning of stormy weather on the way.«««

O que se traduz:

»»»O antecessor do moderno barómetro só foi inventado em 1643. Apesar disso, os navegadores Portugueses (pilotos) no século dezaseis usavam um tipo de barómetro "vivo" o qual consistia numa sanguessuga dentro de uma garrafa cheia de água doce. A posição que a sanguessuga tomava dentro da garrafa permitia prever as condições meteorológicas. O sistema era bastante mais sofisticado do que pode parecer. Existiam nada menos do que nove posições que a sanguessuga podia tomar, e os navegadores memorizavam um conjunto de nove versos que indicavam qual a previsão em função da posição da sanguessuga. Como regra empírica básica, quanto melhor sejam as condições meteorológicas futuras, o mais no fundo da água a sanguessuga nadará. Inversamente, quanto mais à superfície se encontrar a sanguessuga maior será a tempestade que se aproxima.««« 

Os factos que o autor se refere no seu livro desenvolvem-se no primeiro quartel do século dezaseis mas as técnicas usadas e desenvolvidas pelos navegadores portugueses têm origem no século quinze com todas as capacidades da época. No caso vertente será um aproveitamento empírico de um fenómeno observado.

O que se pode concluir é que, 150 anos antes do aparecimento do primeiro modelo do barómetro moderno já existia uma possibilidade, arcaica e limitada, de resolver o problema da possibilidade de previsão meteorológica.

A Universidade do Algarve em mais um projecto de investigação ligado ao Mar

Transcrevemos, com a devida vénia, a notícia dada à estampa no jornal "BARLAVENTO" de mais um projecto de investigação que envolve a Universidade do Algarve, projecto ligado ao Mar.

Os Oceanos continuam a ser o futuro da humanidade tal como o foram há mais de quinhentos anos, quase seiscentos, para Portugal e para o Algarve, sendo de assinalar que a Universidade do Algarve esteja na primeira linha.

Universidade do Algarve lidera projecto criação de rede sem fios para comunicar debaixo de água

A criação de uma rede sem fios para comunicar através do som debaixo de água é o objectivo de um projecto que está a ser desenvolvido por vários países europeus, liderado pela Universidade do Algarve (UAlg).

O projecto Underwater Acoustic Network (UAN) visa colocar a rede ao serviço da segurança subaquática de estruturas como plataformas petrolíferas ou instalações de geração de energias renováveis, vulneráveis a diversas ameaças.

Os cinco pontos da rede vão cobrir um perímetro de 100 quilómetros quadrados e permitirão a troca de mensagens entre si através de uma espécie de e-mail, enviando texto e imagens usando ondas sonoras, que se propagam facilmente debaixo de água.

O Laboratório de Processamento de Sinais (SiPLAB) da UAlg é o organismo que lidera o grupo de seis parceiros que participam no projecto e que inclui cinco centros de investigação e empresas da Itália, Noruega e Suécia.

Segundo Sérgio Jesus, coordenador do SiPLAB e do projecto UAN, o conceito chave do projecto é a "mobilidade" e uma rede de comunicação "wireless" subaquática tem grandes vantagens, sobretudo quando aplicada ao serviço da segurança em meio aquático.

Composta por cinco nós - dois móveis, dois fixos e uma estação de base que assumirá o papel de cérebro de toda a operação -, a UAN terá capacidade para cobrir de forma dinâmica um perímetro subaquático de 100 quilómetros quadrados. Todos os nós da rede estarão equipados com vários sensores, necessários para detectar potenciais ameaças a estruturas estratégicas como plataformas petrolíferas ou instalações de geração de energia, tanto em alto mar como em zonas costeiras.

Os diversos sensores captarão informação sobre a temperatura da água, a velocidade das correntes ou a oscilação da coluna de água, monitorizando a todo o tempo o perímetro que defendem. "Os dois nós móveis, ou veículos autónomos subaquáticos, serão cruciais no processo de recolha de informação, uma vez que podem ser destacados para ir a determinada localização", explica Sérgio Jesus.

A controlar as operações estará uma cadeia de sensores, a estação-base, ou seja, uma antena com 60 metros de altura constituída por uma base, uma unidade de telemetria, um "modem" e vários sensores ao longo de um cabo que termina num flutuador abaixo da superfície. Além dos dois veículos autónomos e da estação-base, farão parte desta rede outros dois nós fixos que participam na recolha de informação ambiental estratégica para o processo de vigilância e detecção.

Iniciada em Outubro de 2008, a UAN terá de esperar até Setembro de 2010 para ser testada pela primeira vez em águas italianas, numa operação em que vão participar todos os parceiros do consórcio europeu coordenado pelo SiPLAB.

Em 2011 terá lugar o teste final, na Noruega, sendo que já em Março de 2010 serão efectuados, ao largo de Vilamoura, testes preliminares à estação-base que está a ser desenvolvida na UAlg.

22 de Maio de 2009 07:43lusa

Os Vikings foram os primeiros oceanografos ?

Com a devida vénia transcreve-se o artigo da NewScientist relativo ao assunto onde se vão confirmando que as "sagas" que pertencem ao passado Viking devem ser tomadas com atenção pois mostram-se como verdadeiros primeiros relatos da oceanografia da área do Atlântico que envolve as costas do NW da Europa, NE da América, Gronelêndia e Islândia.

Sagas reveal Vikings were 'first oceanographers'
24 March 2009 by Eric Scigliano
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Norse pioneers chose where to settle by following signs from the god Thor, but the practice was based on sound science too (Image: Bridgeman Art Library/Getty)
When Hallstein son of Thorolf Mostbeard found a suitable homestead on Iceland, he sacrificed to Thor, imploring the god to provide the ceremonial high seat posts he needed to complete his great hall. Evidently Thor heard: a mighty log washed ashore, big enough to supply seat posts for all the settlers round about. Years earlier, when Hallstein's father and other Norse pioneers sailed for Iceland, they had found themselves in the opposite fix. They had brought seat posts from home but needed a good place to settle. As they approached Iceland, they tossed their precious posts overboard and followed them to the places Thor supposedly chose for them. But the two prayers had something in common: the same sound ocean science underlay them both.
OLD Kveldulf knew it was time to get out of Norway. He had pushed his luck by refusing to swear allegiance to Harald Tanglehair - a king not to be trifled with. When the king slew his son Thorolf, Kveldulf went berserk. He and his surviving son Skallagrim ambushed two of the king's emissaries, killing them and 50 companions, and fled to sea.
Luckily, safer shores awaited them. This was the 9th century and Norsemen had lately begun to settle Iceland, a thousand kilometres to the west. As they sailed, though, father and son's ships became separated. Exhausted by his killing spree, Kveldulf felt his strength slipping away, as the Norse sagas tell us often happens to berserkers when they come down. When he felt he was close to death he instructed his companions to "make me a coffin, and put me overboard" that he might "come to Iceland and take land there", and to tell his son "that if he reaches Iceland and I am there already, to make himself a home as close as possible to the place where I have come ashore". They obeyed, and later chanced upon the coffin washed up in a creek entering the firth called Borgarfjord. Skallagrim dutifully built his farmstead there and prospered.
Strange as his last wish might sound, Kveldulf was not merely exercising an old man's whim. He was following what was already a hallowed tradition among Norse explorers, a tradition that made oceanographers of Kveldulf and his fellow Vikings.
The practice goes back to the first recorded Norse settler in Iceland: Ingolf Arnarson, who fled Norway in 874 after a killing. As Ingolf approached the island, he threw his öndvegissúlur, his high seat posts, overboard. This was no frivolous gesture; these pillars, often carved with an image of the god Thor, framed the high seat in a Norse great hall where the master of the house sat, and were infused with totemic power and family symbolism. But Ingolf had no intention of losing his, any more than Kveldulf had of being lost. He landed on Iceland's south coast and sent his slaves westward to find the posts. Where they found them, he made his home - at Reykjavik, Iceland's capital to this day.
As more fugitives and emigrants followed Ingolf, seat posts and other precious wooden objects flew off the longboats. Bjorn Ketilson, who was also fleeing King Harald's wrath, found his posts - and settled - where the steep walls of Breidafjord opened onto an appealing beach. His sister Unn the Deep-Minded, shipwrecked at Vikrarskeid, overwintered with her brother and then found her seat posts at the head of Hvammsfjord, near today's village of Hvamm. Hasteinn Atlason jettisoned his setstokkar, the partition beam from his old hall, and followed it to his new home.
What prompted the Vikings to risk their precious heirlooms this way? The tale of Thorolf Mostbeard, recounted in the Eyrbyggja saga, offers one explanation. Thorolf, a "great friend" of Thor, was obliged to flee after he sheltered Bjorn Ketilson from King Harald. He made a sacrifice and asked Thor what he should do. Sail for Iceland, the thunder god replied. Cast your seat posts upon the waters and follow where I take them. Thorolf obeyed and, where the posts washed up, he built a great temple dedicated to Thor and declared the site a sanctuary where killing and defecation were strictly forbidden. Alas, one faction among his successors refused to observe the second of these prohibitions, and the faithful non-defecators drove them off in a fierce onslaught.
Cast your seat posts upon the waters and follow where I take them, replied Thor
For a millennium after these accounts were recorded, they lay buried in the sagas. Then, in 1962, in an otherwise conventional doctoral dissertation on the waters around Iceland, a young oceanographer called Unsteinn Stefansson re-examined the tales. The jettisoned posts, he wrote, were the "drift bottles" of their day, markers that helped the settlers discern the currents around Iceland.
Stefansson's insight might likewise have been filed and forgotten, except that soon afterwards he visited the University of Washington in Seattle and presented a leather-bound copy of his dissertation to oceanographer Cliff Barnes. Barnes had a particular interest in North Atlantic drifters: during the second world war he had helped allied convoys thread the safest route between the icebergs and German U-boats by tracking the icebergs that calved off Greenland.
In the 1980s, Barnes was incapacitated by Alzheimer's and his protégé Curt Ebbesmeyer inherited his papers. Ebbesmeyer (with whom I've written a book, the forthcoming Flotsametrics and the Floating World) came across Stefansson's dissertation and decided to follow the clues he had left. Delving further into the sagas and the minutiae of Icelandic geography, he plotted the drift routes of Kveldulf's coffin and sundry seat posts and reached a surprising conclusion.
The Icelanders knew well what treasures the currents could carry. They collected sea beans, floating seeds from tropical America widely believed to bring good luck, and washed-up logs from Siberia and the Americas. Such wash-ups can be vital to those who live on islands with limited supplies of timber. Even on the relatively lush Hawaiian islands, Polynesian kings needed drift logs from America's west coast to build their giant war canoes. The esteem in which such flotsam was held is evident from the account of one 19th-century missionary to Hawaii, Titus Coan. He wrote how a native assistant helping to translate a Pauline epistle stumbled over the word "virtue" until he found a Hawaiian equivalent - "a stick of Oregon pine".
Driftwood was needed even more on nearly treeless Iceland and the washed-up seat posts marked beaches where it accumulates. "Wood follows wood," says Ebbesmeyer. Other valuable flotsam, such as beached whales, concentrated there and marine mammals also took advantage of the currents to haul out. Kveldulf's son Skallagrim found that the firth where his father's coffin washed up offered "seal-hunting in plenty, and good fishing".
Thor's instructions were "sound practical oceanography", says Ebbesmeyer. After plotting their jetsam's arcing drifts around southern and western Iceland, he believes the Vikings deduced that a current circled the entire island, the first recorded discovery of an oceanic gyre. "I'd have to call the Vikings the first oceanographers."
The idea is so practical that Ebbesmeyer thinks the Norsemen probably practised the same sort of oceanographic observation in Norway, although he hasn't found any evidence. He hopes others will follow the trail Stefansson began when he dared to open his dissertation with data derived from ancient tales generally dismissed as legend. "It was brave of him," says Ebbesmeyer. "Even anthropologists did not take the sagas seriously. They did not believe the sagas when they said that Vikings had reached America. Then the discovery of the Viking settlement at l'Anse aux Meadows changed all that. We need to listen to the sagas more carefully."
Perhaps future discoveries of far-floating seat posts will pique rather more interest. So many eddies spin off the currents circling Iceland that Ebbesmeyer thinks most jettisoned artefacts would have been borne away from the island to Norway, to North America and, via the Norwegian and North Atlantic Currents, to the Arctic, where some may have lain a thousand years encased in ice. Now the Arctic is thawing. Perhaps Thor's drifters will emerge to beckon future emigrants - refugees from a baking planet rather than a vengeful king - to new homes in the once-frozen north.

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