ESA - Eduspace EN - Global Change - The Islands of Kerguelen

Coastal change

Danube Delta change detection Oil spills

Deforestation

Bardia National Park Congo River Basin Kameng-Sonitpur Elephant Reserve Kilimanjaro Rondonia Shillong and Guwahati

Ice

Antarctica 2003 Climate change and glaciers Glacier analysis using radar imagery Glacial retreat in the Alps Glacier Ice Flow Monitoring of glaciers in the Himalayas Remote sensing of ice and snow

Urbanisation

Cairo City of Kathmandu Córdoba Himalayas Kathmandu Valley Lagos

Vegetation

Annapurna Conservation Area Lost in the Andes Ngorongoro Conservation Area Niger Inland Delta Vegetation in South America

The Islands of Kerguelen - Continued

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Radar stereo image of Kerguelen Islands

You may also notice that the sea is coloured on this image. Can you explain why? Think of the fact that this image is a combination of two images taken on different days, and think of the ever-changing wind conditions.

While orbiting the Earth, Envisat's radar always looks to the right. In these scenes, the westernly exposed slopes are brightly illuminated. This means that the satellite passed over the area coming from the south, hence on the night-side of the globe. In fact, it was 18:17 GMT, or 23:17 local time, when the satellite passed over the area. As mentioned already, radar does not need sunlight. It uses its own microwave resources to 'illuminate' the scene.

There was only local wind at that time of the night. And looking at the huge tongue-like feature on the sea just west of the glacier dome, we can identify the effect of the descent of cold and heavy air spreading out from the valleys into the sea – this is a typical nighttime valley wind in mountainous areas. We do not see the wind, but just the effect of it on the sea surface.

During her short stay at Kerguelen, our young scientist onboard the icebreaker also took samples from the sea and measured, among other things, its chlorophyll concentration.

When the icebreaker passed the island, our student took water samples at 49-23 South and 70-05 East and assessed the chlorophyll concentration. This allowed us to compare the measurement taken on the ground with the one made by the Envisat satellite at an altitude of 800 km. We do, however, have to keep in mind that onboard the ship only a few litres of seawater is analysed, while the satellite covers an area of around 1200 m x 1200 m for one measurement.

Look it up in the list of the 'resultats-chimie-chlorophyll' table file. Envisat flew over and measured the colours of the sea surface with its MERIS visible-infrared scanner.


	MERIS image of Kerguelen Islands (natural colour)

MERIS031114_054501_Kerguelen.jpg shows the island and the vicinity in real colour. We can hardly recognise the island, a grey surface in the upper left section, close to the image centre.


MERIS image of Kerguelen Islands (chlorophyll colour)

MERIS031114_054501_Kerguelen.bmp shows a colour representation of the chlorophyll concentration ranging from low (green) to red and yellow (high). We can observe a high concentration towards the top right corner. This might be caused by an upwelling zone where cold Antarctic and cool mid-latitude water meet.

There is more about how to measure chlorophyll concentration in the 'chlorophyll concentration exercice' you find on the right.

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