180.

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similar basis, but use a synthetic rather than a real antenna. They are known as synthetic aperture radars (SAR).

1.6.1 SLAR image resolution

SLAR transmits and receiving microwave energy using an antenna located to the side of the platform. The area imaged by the sensor is thus a strip of ground parallel to the flight track (known as the azimuth direction). SLAR image resolution is mainly dependent on pulse duration and antenna beam width, which is the ground area ‘illuminated’ by the radar pulse at a given instant in time (Figure 1.13). Pulse duration affects the resolution in the range (cross track) direction, while antenna beam width controls the azimuth (along track) resolution. The ground range resolution and azimuth resolution are computed by:

(1.23)

(1.24)

The term c is defined in Equation (1.22), while τ is the pulse duration, θ is the depression angle defined as the angle between the horizontal plane and the direction of emitted microwave energy (Figure 1.13), d is the ground range, and β is the antenna beam width. Range resolution can also be analysed in terms of incidence angle or look angle (Figure 1.13). Incidence angle is defined as the angle between the radar beam and a line

Figure 1.13 Some basic parameters of a SLAR system.

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