SPEX airborne spectro-polarimeter operational performance
Abstract
High accuracy multi-angle polarimetry is of crucial importance for remote sensing of aerosol properties with accuracies demanded by climate and air quality studies. In this contribution, wed present an inter-comparison of two airborne multi-angle polarimeters: the Dutch "SPEX airborne" spectro-polarimeter and NASA's "Research Scanning Polarimeter" (RSP).
The two instruments flew together on-board NASA's high altitude research aircraft ER-2, during the ACEPOL campaign in October-November 2017 which included a total of four polarimeters and two lidars. Simultaneous measurements were made while flying over widely different scenes, under different illumination and meteorological conditions. This provided a large dynamic range in radiometric and polarimetric values. We found that the Degree of Linear Polarization (DoLP) measured by both instruments agrees very well with an RMS difference of ~0.005. Also for the radiance the agreement is good with a RMS difference of ~4%. RSP has a long-standing track record of flights. With RSP being equipped with in-flight calibration, its measurements are considered to be among the best to-date. The in-flight comparison results provide verification of SPEX airborne's capability to deliver high-quality data. SPEX-airborne is a multi-angle viewing instrument providing snapshot measurements of spectral radiance and degree of linear polarization at fixed viewing angles over a moderate swath. Radiance and polarization are measured as a continuous function of wavelength in the 400-800nm range, at nine viewing angles equally distributed over an angular range of -56° to +56°. Each viewing aperture has a swath of 7° with an IFOV of 0.5°x1° (cross- times along-track). RSP delivers radiance and polarization measurements continuously over viewing angle, with six VNIR and three SWIR wavelength bands. It has an IFOV of 0.8°x0.8°. Both instruments have a demonstrated on-ground polarization accuracy of ~0.2%. We present an inter-comparison approach that evades precise geolocation of the data and associated errors. Possible sources of error that limit the comparison to the stated level are discussed. Our analysis contributes to the ACEPOL objectives to compare capabilities of different polarimeters for retrieval of aerosol microphysical and optical parameters. Proven SPEX airborne performance is relevant for SPEXone, a small satellite limited-swath multi-angle polarimeter that builds on SPEX airborne heritage and space-borne spectrometer heritage within the Netherlands. SPEXone is being developed for the NASA PACE mission, which has a planned launch date in August 2022.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A13A..02S
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0319 Cloud optics;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0360 Radiation: transmission and scattering;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 4275 Remote sensing and electromagnetic processes;
- OCEANOGRAPHY: GENERAL