Hinds Custom PEM Plays a Key Role in NASA-sponsored project
April 13th, 2007
Multiangle SpectroPolarimetric Imager
Hillsboro, Oregon, April 13, 2007 - Hinds Instruments, the leading global supplier of photoelastic modulators (PEMs), today announced it is working closely with NASA's Jet Propulsion Laboratory (JPL) to integrate spectropolarimetric sensing into a candidate next-generation remote-sensing satellite imaging system. Sponsored by NASA's Instrument Incubator Program, the goal is to enhance the coverage, spatial resolution and accuracy of tropospheric aerosol measurements, thereby reducing uncertainties in predicting climate change and making possible more detailed, comprehensive measurements of global particulate pollution.
A unique benefit of polarimetry is its high sensitivity to particle refractive index. Combined with multiangle and multispectral techniques, this will provide researchers with new tools to better understand how aerosols scatter and absorb solar energy that enters and exits the Earth's atmosphere and how aerosols affect the brightness and lifetimes of clouds. JPL is developing the Multiangle SpectroPolarimetric Imager (MSPI) to take the next step beyond two current in-orbit spaceborne aerosol imagers, the Multiangle Imaging SpectroRadiometer (MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), and the high-accuracy but non-imaging Aerosol Polarimeter Sensor (APS) scheduled for launch on NASA's Glory mission. MISR, MODIS and APS each provide unique strengths for the measurement of tropospheric aerosol column bundances and microphysical properties, and MSPI is designed to integrate several of their key characteristics into a single instrument.
The PEM was chosen over other polarization modulation techniques for several reasons. The system specifications call for measurement of the degree of linear polarization (DOLP) with an uncertainty of 0.5% or better over a wide field of view at moderately high spatial resolution. PEMs are suitable for such imaging applications because they are precision devices with a wide angle of acceptance. They are also free of the mechanical wear of rotating waveplates and the aging of organic materials such as liquid crystals. The low power requirements of PEMs are more appropriate for spaceborne applications than Kerr or Pockels cells.
To meet the project's demands, Hinds Instruments created a ruggedized version of its 42-kHz Series-II PEM system. The device employs dual PEMs within a reflective camera design. The dual PEMs vibrate at slightly different resonant frequencies; this results in modulation of the polarized light at a heterodyne frequency optimized for NASA's spaceborne application.
"Optimizing a PEM system to survive a launch was a great challenge," said Chad Mansfield, mechanical engineer with Hinds Instruments. "JPL provided design guidance including technical expertise, a rigorous design review environment and ultimately vibration testing that simulated a launch, shaking it with 15 g's over a typical spectrum. Thanks to a novel PEM support designed by the Hinds R&D team our device met the requirements."
Hinds Instruments is the world leader in developing and supplying polarization modulation components (or photoelastic modulators) for a broad range of applications. With 30+ years of polarization modulation experience, Hinds Instruments PEMs are proven tools for laboratory and research applications. PEMs operate on principles of resonance (20-84 kHz), require low power and have no moving parts. Hinds' family of products includes modulators, optical choppers, Stokes polarimeters and birefringence measurement systems. For more information, please contact Hinds Instruments.