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The Earth Sciences Decadal Survey identifies a multiangle, multispectral, high-accuracy polarization imager as one requirement for the Aerosol-Cloud-Ecosystem (ACE) mission. JPL has been developing a Multiangle SpectroPolarimetric Imager (MSPI) as a candidate to fill this need. A key technology development needed for MSPI is on-board signal processing to calculate polarimetry data as imaged by each of the 9 cameras forming the instrument. With funding from NASA's Advanced Information Systems Technology (AIST) Program, JPL is solving the real-time data processing requirements to demonstrate, for the first time, how signal data at 95 Mbytes/sec over 16-channels for each of the 9 multiangle cameras in the spaceborne instrument can be reduced on-board to 0.45 Mbytes/sec. This will produce the intensity and polarization data needed to characterize aerosol and cloud microphysical properties. Using the Xilinx Virtex-5 FPGA platform, a polarimetric processing least-squares fitting algorithm is under development to meet MSPI's on-board processing (OBP) requirements. The Virtex-5 FPGA is not yet space-flight qualified; however, an in-flight validation of this technology on a pre-cursor CubeSat mission is valuable toward advancing the technology readiness level for MSPI and the ACE mission.

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The multi-angle spectro-polarimetric imager (MSPI) is an advanced camera system currently under development at JPL for possible future consideration on a satellite based Aerosol-Cloud-Environment (ACE) interaction study as outlined in the National Academies 2007 decadal survey. In an attempt to achieve necessary accuracy of the degree of linear polarization of better than 0.5%, the light in the optical system is subjected to a complex modulation designed to make the overall system robust against many instrumental artifacts that have plagued such measurements in the past. This scheme involves two photoelastic modulators that are beating in a carefully selected pattern against each other [1]. In order to properly sample this modulation pattern, each of the proposed nine cameras 1 in the system needs to read out its imager array about 1000 times per second, resulting in two orders of magnitude more data than can typically be downlinked from the satellite. The onboard processing required to compress this data involves least-squares fits of Bessel functions to data from every pixel, effectively in real-time, thus requiring an on-board computing system with advanced data processing capabilities in excess of those commonly available for space flight.In order to meet the MSPI onboard processing requirements, we evaluated a Xilinx Virtex-4FX60 field programmable gate array (FPGA). In addition to configurable hardware capability, this FPGA includes PowerPC405 microprocessors, which together enable us to pursue a combination hardware/software processing system. This approach allows us to efficiently partition the processing system, using software for algorithmically complex tasks and hardware for more computationally intensive ones. In order to increase performance and/or meet data flow requirements we have developed a system that consists of hardware-based data-capture and least-squares Bessel function fitting and software-based transcendental function computation. We compare the capabilities of this system, and the V4FX60 accordingly, with the requirements of the MSPI camera system. 2, 3 1 Number of cameras is not finalized; may be 7-9. 2 978-1-4244-2622-5/09/$25.00 ©2009 IEEE.