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Page 35

1.7.1 Radar polarisation state

Normally, microwave energy transmitted and received by a radar antenna can travel in all directions perpendicular to the direction of wave propagation. However, most radar systems polarise microwaves in such a way that the transmitted and received waves are restricted to a single plane perpendicular to the direction of wave propagation (Figure 1.20). The polarised wave is therefore transmitted and received in either the horizontal (H) or the vertical (V) plane. Consequently, there are four combinations of transmission and reception for the polarised waves. These combinations are HV, HH, VV, and VH, where HV denotes wave transmitted in V direction and received in H direction. The other combinations can be inferred in a similar manner. Radar imagery generated in terms of HH or VV is called co- or like-polarised imagery, while imagery resulting from HV or VH polarisation is called cross-polarised imagery. Cross-polarisation detects multiple scattering from the target and thus generally results in weaker backscatter than that measured by a co-polarisation configuration.

The co-ordinate system shown in Figure 1.20 determines the radar polar

Figure 1.20 Polarised microwaves.

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Classification Methods for Remotely Sensed Data
Classification Methods for Remotely Sensed Data, Second Edition
ISBN: 1420090720
EAN: 2147483647
Year: 2001
Pages: 354

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