The Hyper-Angular Rainbow Polarimeter-2 (HARP2) was launched on board the Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) mission, in February 2024, for the global measurement of aerosol and cloud properties as well as to provide atmospheric correction over the footprint of the Ocean Color Instrument (OCI). HARP2 is designed to collect data over a wide field of view in the cross-track direction (+/-47deg) allowing for global coverage in about two days, as well as an even wider field of view in the along-track direction (+/-54deg) providing measurements over a wide range of scattering angles. HARP2 samples 10 angles at 440, 550, and 870nm focusing on aerosol and surface retrievals, and up to 60 angles at 670nm for the hyper-angular retrieval of cloud microphysical properties. The HARP2 instrument collects three nearly identical images with linear polarizers aligned at 0°, 45°, and 90° that can be converted to push-broom images of the I, Q, and U Stokes parameters for each angle, and each wavelength. The HARP2 technology was first demonstrated with the HARP CubeSat satellite which collected a limited dataset for 2 years from 2020 to 2022. HARP2 extends these measurements to a full global coverage in two days, seven days a week.
The Hyper-Angular Rainbow Polarimeter (HARP2) is a novel wide-field of view imaging polarimeter instrument on the recently-launched NASA Plankton Aerosol Cloud ocean Ecosystem (PACE) mission. Since launch on February 8 2024, HARP2 has taken over 6 months of global Earth data. In order for this data to meet scientific quality standards, we must ensure that it is as accurate as possible and over long periods of time. We use well-characterized Earth targets, such as Saharan deserts, as well as regular views of the Sun and dark frames to trend our on-orbit calibration. In this work, we discuss the preliminary performance trends derived from these activities and how well they compare with the HARP2 prelaunch calibration.
The Hyper-Angular Rainbow Polarimeter (HARP) Cubesat started data collection in April 2020 from the ISS orbit and is the first Hyper-Angular imaging polarimeter in space. The HARP payload produces pushbroom images at four wavelengths (440, 550, 670 and 870nm) with up to 60 viewing angles at 670 nm and up to 20 along track angles for the other three wavelengths. HARP swath consists of 94 degs in the cross track direction, allowing for a very wide coverage around the globe, and +/-57 degs in the along track direction, providing wide scattering angle sampling for aerosol and cloud particle retrieval. The HARP satellite is still active on orbit and so far have produce a large collection of scenes providing an unprecedented demonstration of the hyperangular retrieval of cloud and aerosol properties from space. This presentation will discuss the performance of the HARP sensor in space, as well as its first results for aerosol and cloud measurements. HARP is preceded by its airborne version, the AirHARP instrument, which has flown in two NASA aircrafts to demonstrate the capabilities of the HARP payload. The HARP payload is also a precursor to the HARP-2 polarimeter that will fly on the NASA PACE mission to collect global data on aerosol and cloud particles.
The design and construction of wide FOV imaging polarimeters for use
in atmospheric remote sensing requires significant attention to the
prevention of artificial polarization induced by the optical elements.
Surface, coatings, and angles of incidence throughout the system must
be carefully designed in order to minimize these artifacts because the
remaining instrumental bias polarization is the main factor which
drives the final polarimetric accuracy of the system. In this work, we
present a detailed evaluation and analysis to explore the possibility
of retrieving the initial polarization state of the light traveling
through a generic system that has inherent instrumental polarization.
Our case is a wide FOV lens and a splitter device. In particular, we
chose as splitter device a Philips-type prism, because it is able to
divide the signal in 3 independent channels that could be
simultaneously analyze to retrieve the three first elements of the
Stoke vector (in atmospheric applications the elliptical polarization
can be neglected [1]). The Philips-type configuration is a versatile,
compact and robust prism device that is typically used in three color
camera systems. It has been used in some commercial polarimetric
cameras which do not claim high accuracy polarization measurements
[2]. With this work, we address the accuracy of our polarization
inversion and measurements made with the Philips-type beam divider.
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