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Satellite observation of an intertidal zone

The two images below show an intertidal zone observed in high and low tidal conditions by the synthetic aperture radar (SAR) on-board the ERS-1 satellite. The area is located at about 25 km north of Port Klang, Malaysia.

High Tide Image (ERS SAR) High Tide Image (ERS SAR)

Acquisition date: 10 May 1996
Time of acquisition: 11:34:58 am (Local Time)
High water time: 10:58 am
© ESA 1996
Low Tide Image (ERS SAR) Low Tide Image (ERS SAR)

Acquisition date: 17 October 1997
Time of acquisition: 11:34:45 am (Local time)
Low water time: 1:01 pm
© ESA 1997

High Tide Image (ERS SAR) shows the land distinctly demarcated from the sea during high tide. Low Tide Image (ERS SAR) shows that a strip of intertidal mud or sand flat along the coast is exposed during low tide. This intertidal zone of more than 20 km long extends as far as two kilometres away from the high tide coastline. The mud or sand flat appears dark in the synthetic aperture radar image due to its generally smooth surface. The brighter structures observed near the river mouth are probably the sand ridges or rocks exposed during low tide.

The river in the middle of the image cuts its course through the mud flat before discharging into the sea. This feature is submerged and not observable in the high tide image. Strips of natural slicks are observed in the low tide image. These natural slicks are probably associated with biological activities in the intertidal zone.

Low Tide Image (SPOT Multispectral) Low Tide Image (SPOT Multispectral)

Acquisition date: 20 January 1999
Time of acquisition: 12:01:54 (local time)
© CNES 1999 Reprodced by CRISP (Singapore) under license from SPOT IMAGE
© Centre for Remote Imaging, Sensing and Processing (CRISP) National University of Singapore

This is a multispectral image of the same area around the river outlet acquired by the SPOT satellite during low tide. The red area is vegetated land while the mud or sand flat appears as grey strip along the coast. The small white patches in the image are clouds, and the adjacent dark patches are the shadows cast by the clouds.