Thinking Outside of the Box can be Over the Moon
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In the engineering profession, one often is presented with high-level requirements with which a design must comply. Experience suggests that such requirements never should be taken for granted. Rather, requirements should be scrubbed to look for potential opportunities or over-specification, which, if discovered, may be exploited to expand the compliant design space beyond traditional constraints, thus opening up potential solutions that are more satisfactory than traditional approaches.
The two Mini-RF radars illustrate this strategy. The imaging radar aboard India’s lunar Chandrayaan-1 satellite was the first polarimetric SAR beyond Earth orbit. The architecture of that radar’and of its more advanced two-frequency sibling on NASA’s Lunar Reconnaissance Orbiter’is hybrid dual-polarimetric, unprecedented for imaging radars. The dual-received data are orthogonal linear polarizations while the transmitted polarization is circular. The dominant science requirement for these lunar radars was measurement and mapping of the circular-polarization ratio (CPR), defined in Earth-based radar astronomical terms as the power ratio of the same-sense (SC) to the opposite-sense (OC) of circularly polarized backscatter, relative to the sense of the transmitted circular polarization. CPR measurement requires transmission of circular polarization. The original requirement for the design was that the receiving system should be dual-circulary-polarized so that traditional SC and OC imagery could be generated. After deeper thought, that requirement was exposed as over-specified. Thinking outside of the box revealed that classical fundamental principles could be applied to expand the design space for the receiver, leading to a new and better configuration. Rather than imagery, the primary data product of the Mini-RF radars was stipulated to be the 2Ï &rquo;2 covariance matrix of the backscattered field, leading to a paradigm shift in imaging radar design. The resulting hybrid-polarity architecture is an ideal response to the requirements for the lunar Mini-RF SARs; maximal science provided through minimal hardware.
R. Keith Raney received his B.S. degree with honors in physics from Harvard University in 1960, his M.S.E.E. degree from Purdue University in 1962, and his Ph.D. degree in Computer Information and Control from the University of Michigan in1968. He contributed to the design of NASA's Venus orbital radars Pioneer and Magellan, the ERS-1 microwave AMI instrument of the European Space Agency (ESA), and NASA’s Shuttle Imaging Radar SIR-C. While with the Canada Centre for Remote Sensing (CCRS, 1976-1994), Dr. Raney was scientific authority for the world's first digital processor for the SeaSat synthetic aperture radar (SAR), and responsible for the conceptual design of the Radarsat-1 SAR. The radar altimeter design on ESA’s CryoSat-2 is based on his original concept, and he is the design architect for the Mini-RF hybrid-polarity radars on India’s Chandrayaan-1 and NASA’s Lunar Reconnaissance Orbiter. Dr. Raney has authored over 400 publications and holds U.S. and international patents on various aspects of radar. Review and advisory committee service includes the Office of Naval Research, the National Academy of Sciences, ESA, the Canadian Space Agency, Germany’s Helmholtz Society, the Danish Technical Research Council, ONERA (France), and the Indian Space Research Organization (ISRO). He is a Fellow of the Electromagnetics Academy, and an Associate Fellow of the Canadian Aeronautics and Space Institute. Awards include the IEEE Geoscience and Remote Sensing Society 1993 Distinguished Achievement Award, the 1999 CCRS Gold Medal, the IEEE Millennium Medal 2000, and the IEEE 2007 Dennis J. Picard Medal for radar technologies and applications.