Advancing Radar Technologies for Space Exploration

Microwave radar imaging systems have proven themselves to be an indispensable tool for scientific exploration, but it could also be argued that the capabilities of contemporary systems thus form a bottleneck that serves to restrict the pace of scientific discovery. In recognition of this, the proposal “Advancing Radar Technologies for Space Exploration” was submitted to the NASA Space Technology Research Fellowship program in 2011 to advance the goal of continued improvement in the technologies that enable radar imaging systems to facilitate exploration of the earth and the surrounding universe. The two-fold goals of this project have been to analyze and demonstrate next-generation techniques for microwave radar imaging, particularly by exploring the convergence of rising interest in both software defined and Multiple-Input Multiple-Output (MIMO) radar systems. This report details the outcomes of this four-year fellowship project which have included the development and demonstration of one of the world’s first waveform-diverse MIMO synthetic aperture radar imaging systems. Coverage also includes a brief introduction to this work and a synopsis of published articles, conference presentations, on-site experience outcomes, and plans for the future. The final MIMO SAR measurement used much of the same approach from the stationary target measurement trials. Targets were again imaged in both TDMA and MIMO modes so that the coherent subtraction of these images could be compared. An example image is shown below for a top hat reflector imaged against a mown grass background. Results once again show a good agreement between the images. Both TDMA and MIMO images clearly show the presence of the target as well as a consistent presentation of the background clutter, and even disagreements that are detected are more than thirty decibels below the target’s magnitude. A weaker subtraction is seen along the target’s range arc, and this is most likely due to the lower dynamic range of this measurement as compared to the stationary target trials. While analysis of this data will continue, results such as these provide some of the first experimental data from a practical MIMO SAR system, and their production is one of this project’s most significant outcomes. The primary objective of this fellowship was the assembly and demonstration of a waveform-diverse MIMO SAR system, and this has been accomplished. Data from the experiments described above represents some of the first experimentally-derived information available about the performance of MIMO SAR systems, and it is hoped that this information will go a long way towards informing the debate over the practical applications of MIMO radar imaging techniques. While the experiments performed as a part of this project are greatly limited in range and scale as compared to many contemporary remote sensing systems, results here seem to indicate that waveform-diverse MIMO imaging may be a viable option for certain applications. Results here have clearly shown that images can be formed using MIMO techniques that retain much of the quality of more traditional approaches. Likewise concepts such as the virtual array and post-processed beamforming have been demonstrated by these measurements, and their successful application here is another promising indication that the practical benefits of MIMO systems can be realized despite the presence of notable obstacles.