Advances in Multiangle Imaging for Future Satellite Systems

Since February 2000, the Multi-angle Imaging SpectroRadiometer (MISR) has been acquiring global cloud and aerosol data from its vantage point on the Terra polar-orbiting satellite. MISR acquires moderately high-resolution imagery at nine along-track view angles ranging from 70.5º forward to 70.5º backward of nadir, in four visible/near-infrared spectral bands. Visible wavelength stereophotogrammetry affords major benefits for measuring cloud-top heights (CTH) and cloud-tracked winds (CTW): long-term temporal stability, independence from atmospheric thermal structure, high horizontal and vertical spatial resolution, and pole-to-pole coverage. A new version of MISR's stereo cloud product was released in 2012, providing improved accuracy, coverage, and spatial resolution of the height-resolved CTW. A MISR spinoff concept, the Multiangle Stereo Imager (MSI), is a wide-angle pushbroom camera employing multiple line arrays in a custom CCD architecture to leverage MISR algorithms in a compact, low-mass, low-power, and low-cost instrument. A constellation of three MSI instruments in polar Earth orbit would obtain height-resolved cloud-motion wind fields in 1200-km wide swaths. With daily global coverage MSI would be a low-cost complement to a spaceborne lidar wind measurement system. Tandem MSI instruments in the same orbit plane, separated by 5-10 minutes of flight time, would yield wind uncertainties of <0.5 m/s, and provide sensitivity to vertical winds in rapidly developing convective systems. Another MISR spinoff concept is the Multiangle SpectroPolarimetric Imager (MSPI), aimed at measurement of aerosol and cloud microphysical properties. With multiple cameras at fixed angles, MSPI is a candidate for the National Research Council Decadal Survey's Aerosol-Cloud-Ecosystem (ACE) mission, and combines the capabilities of MISR with those of other aerosol sensors, extending the spectral coverage to the ultraviolet and shortwave infrared and incorporating high-accuracy polarimetric imaging using photoelastic modulators. A smaller system consisting of a pointable camera on a 2-axis gimbal could fly as part of a small mission and would enable targeting major metropolitan areas in order to associate different types of airborne particulate matter with human health outcomes. An airborne MSPI testbed, AirMSPI, has been acquiring aerosol and cloud imagery from NASA's high-altitude ER-2 aircraft since 2010. Example imagery and data analysis results will be presented.