Low polarization optical system design

Mahler, Anna Britt; Smith, Paula K.; Chipman, Russell A.

doi:10.1117/12.734932

Cited by 9 publications

(3 citation statements)

References 10 publications

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“…The system is capable of imaging over a ±31° cross-track field of view (FOV), but only the central ±15° is used because the prototype detector array is limited in length. The three mirrors were coated with high-performance thin films to minimize diattenuation (absolute difference divided by the sum of reflectance for light polarized in planes perpendicular and parallel to the plane containing the incident and reflected light) [30].…”

Section: Telescope Optics and Retardance Modulatormentioning

confidence: 99%

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Diner

Martonchik

et al. 2012

Atmosphere

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Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the OPEN ACCESSAtmosphere 2012, 3 592 surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.

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Section: Telescope Optics and Retardance Modulatormentioning

confidence: 99%

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Diner

Martonchik

et al. 2012

Atmosphere

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“…Consequently, the new design must have low polarization aberrations, particularly low diattenuation, requiring custom high-performance coatings [16]. To reduce the time it takes to cover the entire globe from low Earth orbit, the MSPI cameras have twice the cross-track field of view (FOV) of the MISR cameras.…”

Section: Opticsmentioning

confidence: 99%

WindCam and MSPI: two cloud and aerosol instrument concepts derived from Terra/MISR heritage

et al. 2008

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The Multi-angle Imaging SpectroRadiometer (MISR) has been acquiring global cloud and aerosol data from polar orbit since February 2000. MISR acquires moderately high-resolution imagery at nine view angles from nadir to 70.5º, in four visible/near-infrared spectral bands. Stereoscopic parallax, time lapse among the nine views, and the variation of radiance with angle and wavelength enable retrieval of geometric cloud and aerosol plume heights, height-resolved cloud-tracked winds, and aerosol optical depth and particle property information. Two instrument concepts based upon MISR heritage are in development. The Cloud Motion Vector Camera, or WindCam, is a simplified version comprised of a lightweight, compact, wide-angle camera to acquire multiangle stereo imagery at a single visible wavelength. A constellation of three WindCam instruments in polar Earth orbit would obtain height-resolved cloud-motion winds with daily global coverage, making it a low-cost complement to a spaceborne lidar wind measurement system. The Multiangle SpectroPolarimetric Imager (MSPI) is aimed at aerosol and cloud microphysical properties, and is a candidate for the National Research Council Decadal Survey's Aerosol-Cloud-Ecosystem (ACE) mission. MSPI 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. Based on requirements for the nonimaging Aerosol Polarimeter Sensor on NASA's Glory mission, a degree of linear polarization uncertainty of 0.5% is specified within a subset of the MSPI bands. We are developing a polarization imaging approach using photoelastic modulators (PEMs) to accomplish this objective.

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“…Prior to camera alignment, the three mirrors were placed in their approximate nominal positions in the ASPC and the polarization aberrations were measured using the MMIP. The mirror coatings have been optimized such that modeled pupil averaged diattenuation is below 1% [5]. Measurements of the camera diattenuation are shown in Fig.…”

Section: Aspc Polarization Aberration Measurementsmentioning

confidence: 99%

Calibration and performance validation of optical elements in a photoelastic modulator-based polarimetric camera

Mahler¹,

Chipman²,

McClain³

et al. 2008

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium

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As part of NASA's Instrument Incubator Program (IIP), we have been developing enabling technologies for the Multiangle SpectroPolarimetric Imager (MSPI), a candidate instrument for the Aerosol-Cloud-Ecosytem (ACE) mission. ACE is one of several satellite concepts identified in the 2007 National Research Council Earth Sciences Decadal Survey. MSPI is a multiangle, multispectral, high-accuracy polarization imager, and is envisioned to contain multiple cameras pointed at different viewing angles, with intensity imaging in several spectral bands between the ultraviolet and shortwave infrared, and accurate polarimetric imaging in a subset of the bands. To achieve a degree of linear polarization (DOLP) uncertainty of 1%, we temporally modulate the linear-polarization component of the incoming light at a rapid rate, enabling each detector within a focal-plane array-combined with polarization analyzers-to measure the relative proportions of the linear Stokes components Q or U to the total intensity I. Our system uses tandem photoelastic modulators (PEMs) within a reflective camera design. We report on the status of our prototype camera development, with particular emphasis on theoretical and experimental work on the required and measured performance of optical elements within the system including: the spectropolarimetric filters, quarter wave plates, and tandem PEMs. We also report on the end-to-end measurement and calibration of camera polarization aberrations using a custom polarization state generator (PSG). Careful design and control of scattered light enables the PSG to generate polarization states between DOLP of 0.07% and 40% with an uncertainty of 0.05%, making it a precision tool for polarimetric calibration and validation of MSPI.

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Low polarization optical system design

Cited by 9 publications

References 10 publications

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

WindCam and MSPI: two cloud and aerosol instrument concepts derived from Terra/MISR heritage

Calibration and performance validation of optical elements in a photoelastic modulator-based polarimetric camera

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