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.
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 www.techbriefs.com/tsp under the Electronics/Computers category. NPO-40413
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Detecting Negative Obstacles By Use of Radar
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Overview
The document titled "Detecting Negative Obstacles by Use of Radar" from NASA's Jet Propulsion Laboratory outlines a novel approach to enhance obstacle detection for rovers operating in challenging Martian terrain. Traditional optical systems often struggle with detecting negative obstacles, such as holes and ditches, particularly under varying lighting conditions. To address this issue, the document proposes the integration of low power Frequency Modulated/Continuous Wave (FM/CW) radar technology.
The radar system is designed to point down and ahead of the rover, utilizing shifts in reflection from the Martian surface to identify negative obstacles. The radar operates effectively at wavelengths between 0.2 cm and 10 cm, allowing it to detect features comparable to its wavelength. This capability is particularly beneficial as the radar can penetrate dry Martian soil, providing a reliable means of obstacle detection at short ranges.
The document highlights the commercial availability of similar radar technologies, such as the Forewarn® Back-Up Aid used in high-end luxury vehicles. These systems have been tested at frequencies of 24 GHz and 77 GHz, demonstrating their effectiveness in detecting obstacles at ranges of up to 5 meters. The radar's low cost, simplicity, and robustness make it an attractive option for integration into rover systems.
Key benefits of the proposed radar system include its immunity to lighting and temperature variations, making it suitable for the harsh Martian environment. The radar serves as a "virtual bumper," alerting the rover to stop and assess its surroundings more closely when a potential obstacle is detected. Additionally, the system's signal processing can be managed by a small FPGA or microcontroller, allowing for high integration and low power consumption.
The document also references various literature sources related to automotive collision avoidance systems and radar technology, emphasizing the potential for leveraging existing commercial developments for aerospace applications. Overall, the integration of FM/CW radar technology represents a significant advancement in the capability of rovers to navigate and operate safely in complex Martian landscapes, enhancing their ability to conduct scientific exploration and gather data in previously inaccessible areas.
