700-SDI-RADAR-300WL-Man Rev 2 11 Apr Mar 2022
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Part# 21371
2.6
REFLECTIONS
Water is very reflective medium for the radar waves and most of the power transmitted from radar
transmitter will be reflected from the water surface. Reflections of the radar transmitted power
beam follow the same physical laws as in optics in that part of the power is reflected towards the
radar, part of the power is reflected away from the radar, and a small part of power is absorbed by
the water. Depending on the surface roughness, the incident angle ratio between power reflected
away from the radar and towards the radar can significantly vary.
Figure 2-1: Reflected power
In the case of level meter where the incident angle of the transmitted radar beam (yellow arrow) to
the water is around 90°, most of the power is reflected back to the sensor (blue arrow) and only a
small portion of the transmitted power will be dispersed in all directions (red arrows). In general, the
ratio between power reflected to the sensor and power dispersed in all directions due to surface
roughness is very small and it is unlikely that dispersed energy will cause additional multipath
problems due to additional reflections from surrounding objects.
The situation for the surface velocity radar is little more complex as the angle between the
transmitted radar beam (yellow arrow) and water is around 45°. In calmer conditions, most of the
power is reflected in the opposite direction from the radar (red arrow) at around a 45°. Reflection in
the direction of the radar sensor (blue arrow) is always smaller and can be comparable with the
dispersed power in all directions (gray arrows). However, generally, a rougher water surface will lead
to a stronger reflection being returned to the radar and a greater SNR (signal to noise) ratio which
enables more accurate measurements. The surface velocity radar is designed to achieve accurate
