Using ultra-wideband (UWB) impulse radar for detecting and tracking fast-moving small targets over the ocean surface has been considered before with limited applications. The challenges of deploying such radar sensors on small, unmanned marine platforms are addressed in this study. The first challenge is the stringent size and weight requirement to allow a tracking radar sensor to be fitted into the payload of a small unmanned surface vehicle (USV). For the first time, we implemented a design that is based on a single chip UWB radar sensor operating at X-band, which effectively achieves the size and weight requirement for a small USV payload. The second challenge is range extension and range ambiguity resolution. With the UWB radar operating various high-PRF modes, we developed a novel approach that stitches together range profiles from multiple PRFs, to extend the effective non-ambiguous range at the cost of scan speed. The third challenge is developing a lowcost, ultra-wideband planar antenna and front-end, which is also part of the USV payload and needs to be able to perform either sector scanning, or even electronic scanning, with a very low profile. We have successfully designed and implemented one such antenna using a dipole array design. By integrating the solutions into a complete system, we have performed a series of lab and outdoor tests of the UWB radar sensor and obtained some promising target data. Simulations are also being developed for testing the potential target signatures and tracking effectiveness of moving targets over ocean surface clutter environments.
KEYWORDS: Radar, Calibration, Ka band, Data processing, Signal to noise ratio, Doppler effect, Reflectivity, Antennas, Signal attenuation, Data conversion
Data processing, calibration, and quality evaluation are critical elements for successful airborne radar missions. For a downward-looking airborne radar, the usage of ground as a calibration target has been discussed before but not completely analyzed for precipitation measurement missions at Ka-band. In this study, the team performed data analysis and calibration modeling for the Millimeter-Wave Airborne Radar for Learning and Education (MARBLE), which was developed as a recent undergraduate team effort beginning in 2016. Millimeter-wave radar missions for MARBLE include precipitation measurement and terrain remote sensing through vertical profiling. To achieve these mission goals, the team used multiple time- and spectrum-domain processing methods on the ground return data collected from 2018 NASA ER- 2 engineering calibration flights. Some of the algorithms include spectrum analysis with various CPI arrangement and multi-lag processing to enhance signal-to-noise ratio (SNR). Doppler calibration based on aircraft platform motion and orientation is also considered. Useful results are obtained from ground power calibration as well as Doppler estimation. In addition, multiple ground calibration tests with actual weather results are incorporated to supplement the airborne measurements after some hardware checking and improvement. Based on the reasonable outcomes from the calibration measurements, a new high-altitude flight campaign for precipitation measurement is being planned for 2020.
KEYWORDS: Radar, Antennas, Data modeling, Monte Carlo methods, Reflectivity, Doppler effect, Computer simulations, Phased arrays, Receivers, Signal attenuation
During the design and development of multi-functional airborne hazard detection and avoidance radars, as well as radar navigation functions, we usually need a precise and reliable simulation evaluation. However, the existing solutions are usually highly proprietary for specific developers. In previous studies, we developed PASIM as one possible framework to unify the multi-functional radar developments. In this study, more novel enhancements and applications of PASIM are introduced based on the needs of communities, and the software tools are updated specifically for airborne radars. These updates include: (1) Enhancement and evaluation of airborne radar ground clutter modules, which supports different terrain or water surface types. (2) Combination of measured data as part of simulations. In this case, we used NASA’s pulsed-Doppler weather radar data as “meta-truth” and created simulation examples of a new generation of Sense and Avoid (SAA) simulation operation based on them. (3) Incorporation of realistic target impulse responses, RF channel modeling and processing chain. (4) Incorporation of automatic radar mode optimization, ground clutter mitigation solution and algorithms. (5) Enhanced data quality evaluation for both air-target tracking and weather surveillance. A generic airborne pulsed-Doppler radar with reasonable system parameters are used for our studies as an example and the design/evaluation procedure and results are presented.
The calibration and inspection of various antennas related to navigation, aviation and flight operations has been a big challenge for agencies such as FAA and DoD. These antennas include both ground and airborne components. Antenna systems at ground infrastructure include navigational aide systems such as VOR/LOC, TACAN/DME, and Glide Slope, and include the ground-based surveillance radars. The antennas mounted on the aircraft include various aviation probe antennas and airborne radars. The flight inspection mission requires precise measurement of signal power at locations around any facility. Calibration of airborne radar antenna mounted on aircraft is also needed for precise radar functions. The difficulties, however, lie in the fact that the aircraft body and the environment have significant impacts on the signal measurement quality, which is usually difficult to characterize. This work focuses on how the airframe affects the typical aviation antenna measurements, and a possible way to “normalize” such impacts to gain the desired “effective” radiation patterns. We mainly reply on computational electromagnetic (CEM) tools to establish the physical scattering model of the aircraft with respect to different simplified antenna models, and then validate the radiation patterns through actual flight test data collections. Initial comparisons between the simulations and flight measurements reveal some interesting behaviors of radiation patterns on the aircraft installations, further issue of electromagnetic compatibility in the complex aircraft operations, and the potential of using unmanned aerial systems (UAS) to automate the measurement procedure in the future.
Supported by NASA’s Undergraduate Student Instrumentation Project (USIP), OU-IART worked with Garmin International Inc. to develop a novel, low C-SWaP, high-altitude storm-chasing radar, called MARBLE. The radar operates at 35 GHz (Ka-band), and the concept of operation is flying over the top of a convective storm to measure the reflectivity and vertical motion of the clouds. The system design is extremely simple and low-cost, which uses single-stage up-down conversion between Ka-Band operation and the X-band “base radar transceiver”. The radar is very easy to operate by a pilot, through a simple switch. Laboratory tests and ground verifications were performed, and the system airworthiness has been validated. The systems developments started in spring 2016, and the initial engineering validation flights were performed in Sep 2018, using a NASA high-altitude aircraft (ER-2). Initial flight tests show that MARBLE can operate in high-altitude environments and obtain return signatures from various targets. Further data processing is ongoing to evaluate the effectiveness of precipitation observations. In addition, the design, development and testing process successfully served the educational goals of the program.
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