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Funafuti Atoll, Tuvalu - Continued 
Download a larger version of the Tuvalu radar image (1.6 Mb). One of the other sensors onboard Envisat is the ASAR radar. Recently, this instrument has captured this interesting overview image of the atolls. You can find Vaitupu, Funafuti and Nukufetau in the right (eastern) central part of the image, consisting of very fragile and tiny white and black lines. Perhaps you need to zoom into the image in order to see it better! But what are all the other enormous bulky features? Consider the fact that the image is over 300 km across in both directions. These are footprints of huge thunderstorm clouds! Radar would not show any clouds but just their effect on the surface of the ocean. Such so-called cumulonimbus clouds provoke very strong winds and heavy rainfall, menacing ships and the dwellers of the atolls. The round forms are the gust fronts. The dark spots indicate rainfall, and the very bright spots should represent downpours or extremely heavy rain. Stormy winds and downpours strongly roughen the sea surface, and make it appear bright in the image. Showers, however, dampen the sea waves, making these areas appear as a dark sea surface.
In the image you can also observe a general increase of brightness towards the left. This has nothing to do with phenomena on the ground, but is a consequence of the radar looking steeper towards this end.
Download here a larger version of the Funafuti radar image (1.6 Mb). The Funafuti atoll are shown here in this image taken by Envisat's radar on 10 March 2004. It is a fragile band of land, threatened by high swell and sometimes extreme meteorological conditions, such as storms and typhoons, accompanied by incredible amounts of rain in a short lapse of time. Date of acquission: 4 February 2004 Resolution: 25 metres
The inner part of the atoll seems to be better protected. But is this really the case? Watch the swell travelling southeast on that day. At some point it enters the atoll! Can you spot this? But how is the protection against heavy seas arriving from southwest? Inspect the MERIS images to judge this, since the radar would not show us a reef barrier (microwave does not enter water) but just a change in the wave structure. What is your assessment?
Download here a larger version of the Funafuti radar image (0.2 Mb).
On the eastern coast, where the island is largest, we can spot the main settlement of Tuvalu. There the land is somehow higher, and has a triangular shape. The tiny bright points are houses. Resolution: 12,5 metres
But there is also a long, narrow and straight black line. What can it be? A landing strip?
Let's make some measurements. The size of each pixel in this image is 12.5 m. What is the width of the island in the northern part, what is it across the largest area, and how many metres is it to walk across the island south of the settlement? How long is the landing strip? Find out what type of aircraft would be able to land at Funafuti. In conclusion: The existence of the Tuvalu atolls is based on a fragile equilibrium between constructive and destructive forces.
Name these natural forces and try to quantify them in space and time. Name all possible interference from settlers and from mankind in general, and put them in relation with the natural factors. You may end up constructing a complex environmental model considering long-term phenomena (e.g. coral growth) and singularities like an oil spill, etc. Is such a model also valid for European coastal waters? Last update: 3 July 2013
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