SismoscholarLa sismologia nelle scuole
Le immagini satellitari più belle fornite dall'ESA
This Envisat image captures sea ice and cloud streets in the Svalbard Archipelago, located north of mainland Europe half way between Norway and the North Pole between the Arctic Ocean (top), Barents Sea (bottom right), Greenland Sea (bottom left) and Norwegian Sea.The mixture of heat, moisture and wind over the area has allowed for the formation of cloud streets (thin, white, straight lines). The clouds, commonly found at the border between ice and sea, get their stretched shape through processes related to the high wind speeds at the ice edge.Throughout the image, ice cover is visible breaking into huge chunks. Recent record-lows in the extent of summer Arctic sea-ice cover demonstrate significant changes are occurring in the polar regions. Ice cover has been mapped from space for many years by satellites such as Envisat. However, to understand more about how climate change is affecting these sensitive regions, there was also an urgent need to determine how ice thickness is changing.Data from ESA’s ice mission CryoSat, launched last week, will measure precisely the rates of change of sea and land ice in the Arctic and the Antarctic. Assessing the volume of sea ice in the Arctic has been difficult to do from space because previous missions have not flown far enough to the north to obtain a full view of the Arctic and their instruments have not had the resolution needed to measure the difference between the top of the ice surface and the top of the water.CryoSat is carrying the first radar altimeter of its kind to overcome the difficulties of measuring icy surfaces, and its polar orbit allows it to cover the Arctic up to of 88° north.This image was acquired by Envisat's Medium Resolution Imaging Spectrometer instrument on 13 April 2010, working in Full Resolution mode to provide a spatial resolution of 300 m.
This satellite image shows the ever-moving sandbanks in the shallow Wadden Sea in the north of the Netherlands. Declared a UNESCO World Heritage Site last year, this unique region is one of the largest wetlands in the world.Shaped by the ebb and flow of the tides, waves and wind, the area appears very different depending on the time of day; at times there are kilometres and kilometres of open mud flats full of life and the next moment, awash with incoming waters from the North Sea. These tidal flats and wetlands give rise to an excellent habit for a wealth of wildlife, in particular, an estimated 1.5 million migrating birds.As this satellite image shows, the sandbanks are bordered by relatively deep channels and gullies, which provide a route for boats crossing between the islands and mainland. The image shows the southern part of the Wadden Sea with part of the Dutch mainland on the right and the island of Texel at the bottom left, and Vlieland and Terschelling to the northwest. The impact of waves and currents, which carry away sediment, is slowly changing the layout of these and the other islands further west. For example, the islands of Vlieland and Ameland, which is not visible here but it is the next island after Terschelling, have moved eastwards over the centuries and are being eroded on one side and growing on the other.The Wadden Sea, a name that comes from the Dutch 'wad' for mud flat, extends from the south of Texel, along the coast of Germany to just north of Esbjerg in Denmark, a total length of some 500 km.Also visible in the image is the 'Afsluitdijk' – a causeway that creates a division between the Wadden Sea to the north and the Zuiderzee to the south. Built between 1927 and 1933, this causeway dammed off what was a salt water inlet of the North Sea and turned into a fresh water lake.SPOT-4 acquired this image on 8 May 2006 with a spatial resolution of 20 m. SPOT-4 is supported by ESA as a 'Third Party Mission', which means ESA utilises its multi-mission European ground infrastructure and expertise to acquire, process and distribute data from the satellite to its wide user community. The SPOT system was designed by the French space agency (CNES) and is operated by Spot Image.
This Envisat Advanced Synthetic Aperture Radar (ASAR) composite image shows the Bay of Naples off the west coast of Italy. The bay is lined to the south by the Sorrento Peninsula – where the world-famous Amalfi coast runs along its southern edge. Just beyond the tip of the peninsula lies the beautiful island of Capri. The islands of Ischia, renowned for its thermal springs, and Procida can be seen to the top of the bay.The image clearly displays the signs of volcanism in this region. Formed as a result of the collision between the African and Eurasian tectonic plates, Mount Vesuvius is featured just inland from the bay overlooking the city of Naples. This volcano has erupted many times, most notably in 79 AD when the cataclysmic eruption buried the surrounding area with up to 30 m of ash. The towns of Pompeii and Herculaneum were excavated last century, providing a snapshot of what Roman life was like almost 2000 years ago.The region around this volcano is home to more than three million people and with the last eruption occurring in 1944, it is intensively monitored for signs of unrest.Further signs of volcanism can be seen at the western end of the bay where the Phlegraean Fields lie. This complex structure, most of which is below sea level, is constantly on the move due to subsidence and uplift.This image was created by combining three Envisat ASAR acquisitions taken over the same area. The colours in the image result from variations on the surface that occurred between acquisitions.
This Envisat image captures New Zealand's North and South Islands, separated by the Cook Strait. Named after James Cook, who in 1770 was the first European to sail through it, the Cook Strait connects the Tasman Sea to the west with the South Pacific Ocean to the east. At its narrowest, it is just 23 km wide – so on a clear day it is possible to see across the strait. However, the Cook Strait is also renowned for being one of the roughest and most unpredictable stretches of water in the world.As a result of New Zealand's latitude, the country lies in the path of the westerly wind belt known as the Roaring Forties. Since the strait is the only gap between the mountainous two islands, it acts as a huge wind tunnel, whipping up treacherous seas.In addition, the tidal flow through Cook Strait is unusual. The tide is out of phase, which means when it is high tide on one side it is low on the other, resulting in strong currents in the middle. New Zealand comprises many islands, though the North and South Islands are the largest landmasses. The image shows that the northerly part of the South Island is, in fact, further north that the south of the North Island. The South Island is the larger of these two landmasses and along its length gives rise to the Southern Alps, where the highest peak, Mount Cook, reaches 3754 metres. The North Island is less mountainous but more volcanic.Notable for its geographic isolation in the southwest Pacific Ocean, New Zealand is home to many endemic plant and animal species, although the country has suffered a high rate of extinction due human activity. However, New Zealand is now a world-leader in island restoration programmes, reintroducing native species and establishing wildlife reserves on several smaller islands where pests such as rodents have been eradicated. This image was acquired on 8 March 2010 by Envisat's Medium Resolution Imaging Spectrometer (MERIS) while working in Full Resolution Mode to provide a spatial resolution of 300 metres.
This Envisat image captures the Baltic Sea, with the northern part of the Gulf of Bothnia (top), the Gulf of Finland (right) and the Gulf of Riga (directly below image centre) covered in ice.An arm of the North Atlantic Ocean, the Baltic Sea separates the Scandinavian Peninsula (left) from the rest of continental Europe. The sea is roughly 1610 km long, 190 km wide and has a surface area of about 377 000 sq km, making it the largest body of brackish water in the world.While ice cover varies from year to year, during an average winter about half of the Baltic Sea’s surface is ice covered. As it is a vitally important waterway for transportation and shipping, sea ice can be a major hazard for passenger and commercial vessels during the winter and early spring.This year’s unusual freezing conditions and gale-force winds resulted in the worst ice cover since 1996, causing about 50 cargo and passenger vessels to be trapped in the sea between Sweden (left) and Finland (top centre).The vessels were stuck for several days in early March and had to be freed by icebreaking vessels dispatched by the Swedish Maritime Administration (SMA), which relies on Earth-observation satellite data from the ESA-backed Polar View initiative to coordinate its operations. The SMA also uses Polar View’s sea-ice forecasting service on each of its Finnish and Swedish icebreakers to see how the ice is changing for safe navigation.Polar View, supported by ESA and the EC with participation from the Canadian Space Agency, was established under the EU’s Global Monitoring for Environment and Security (GMES) initiative.The northern basin of the Gulf of Bothnia, known as the Bay of Bothnia, typically ices over in early January, while the Gulf of Finland and the Gulf of Riga usually freeze in late January. Normally, the ice reaches a maximum extent in February or March.Russia’s major city of St. Petersburg is located at the eastern end of the Gulf of Finland and beside it the frozen Lake Ladoga, which is typically frozen from February to May. With a total area of about 18 000 sq km, Ladoga is Europe’s largest freshwater lake and is the main source of drinking water for the inhabitants of St. Petersburg.This image was acquired on 15 March 2010 by Envisat's Medium Resolution Imaging Spectrometer instrument, working in Full Resolution mode to provide a spatial resolution of 300 m.