Because such wavelengths are comparable to the characteristic dimensions of terrain features associated with negative hazards, a significant amount of diffraction would occur at such features. In effect, the diffraction would afford a limited ability to see corners and to see around corners. Hence, the system might utilize diffraction to detect corners associated with negative obstacles. At the time of reporting the information for this article, preliminary analyses of diffraction at simple negative obstacles had been performed, but an explicit description of how the system would utilize diffraction was not available.

A Robotic Vehicle Approaching a Ditch would carry a radar system that
Alternatively or in addition to using diffraction, the system might utilize the Doppler effect and/or the radiation pattern of the radar antenna for detecting negative obstacles. For example, if the forward speed of the vehicle were known, then the approximate direction from the radar apparatus to a reflecting object could be determined from the difference between the Doppler shift of the reflection and the Doppler expected of a reflection from an object straight ahead. For another example, if the main lobe of the radar beam were horizontal or nearly so, then the amount of power reflected from a nearby negative obstacle would be less than that reflected from level ground at the same horizontal distance from the vehicle. Combining these two examples, it might be possible to detect approaching negative obstacles through changes in the reflected power and/or in the spectral distribution of the reflected power.

This work was done by Anthony Mittskus and James Lux of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Electronics/Computers category. NPO-40413

This Brief includes a Technical Support Package (TSP).
Detecting Negative Obstacles By Use of Radar

(reference NPO-40413) is currently available for download from the TSP library.

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