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The advantages of ERS SAR
| Illumination |
SAR is an active system. It illuminates the Earth surface and
measures the reflected signal, generating microwave images of the surface.
Therefore images can be acquired day and night, completely independent
of solar illumination, particularly important at high latitudes (polar
night). |
| Weather independence |
The microwaves emitted and received by the ERS SAR are at a much
longer wavelengts (5.6 cm) than optical or infrared waves. Microwaves can
therefore easily penetrate clouds, and images of the surface acquired irrespective
of local weather conditions. |
| Unique parameters |
Images provided by optical sensors contain information about the surface
layer of the imaged objects (i.e. colour), while microwave images provide
information about the geometric and dielectric properties of the surface
(i.e. roughness) or volume (i.e. chemical composition, moisture) studied,
allowing unique properties of the target to be revealed. |
| Hidden features |
The penetration depth of an incident wave depends partly on its wavelength.
Because of their long wavelength, microwaves are able to penetrate not
only clouds but also features such as soil, sand, snow (in very dry conditions)
or the canopy of a forest, thus providing information about hidden features.
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| SAR-optical complementary applications |
The combined analysis of optical and radar data can provide
unique information not visible in the separate images. |
| Stereo viewing |
Data acquired from slightly different orbits can be combined to produce
stereo images. SAR stereo-pairs can be used to view a scene in three dimensions,
very useful for geological applications, or monitoring ice movement. |
| SAR interferometry |
An exciting new technique has emerged in recent years to utilise ERS SAR
data: Interferometric SAR, or InSAR. Using ERS SAR interferometry, under
suitable conditions, is it possible to generate three-dimensional relief
maps of the Earth's surface. In addition, an extension of the basic technique
allows the detection of very small (order of centimetres) movement of land
surface features, such as Landslides and Earthquakes. |
This page produced by the ERS Data Utilisation Section
RS/ED, 1997
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,
atmospheric chemistry
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