Inversion of multiangular polarimetric measurements from the ACEPOL campaign: an application of improving aerosol property and hyperspectral ocean color retrievals

Abstract

Abstract. NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, scheduled for launch in the time frame of late 2022 to early 2023, will carry the Ocean Color Instrument (OCI), a hyperspectral scanning radiometer, and two multiangle polarimeters (MAPs), the UMBC Hyper-Angular Rainbow Polarimeter 2 (HARP2) and the SRON Spectro-Polarimeter for Planetary EXploration one (SPEXone). One purpose of the PACE MAPs is to better characterize aerosol properties, which can then be used to improve atmospheric correction for the retrieval of ocean color in coastal waters. Though this is theoretically promising, the use of MAP data in the atmospheric correction of colocated hyperspectral ocean color measurements have not yet been well demonstrated. In this work, we performed aerosol retrievals using the MAP measurements from the Research Scanning Polarimeter (RSP) and demonstrate its application to the atmospheric correction of hyperspectral radiometric measurements from SPEX airborne. Both measurements were collected on the same aircraft from the Aerosol Characterization from Polarimeter and Lidar (ACEPOL) field campaign in 2017. Two cases over ocean with small aerosol loading (aerosol optical depth ∼0.04) are identified including colocated RSP and SPEX airborne measurements and Aerosol Robotic Network (AERONET) ground-based observations. The aerosol retrievals are performed and compared with two options: one uses reflectance measurement only and the other uses both reflectance and polarization. It is demonstrated that polarization information helps reduce the uncertainties of aerosol microphysical and optical properties. The retrieved aerosol properties are then used to compute the contribution of atmosphere and ocean surface for atmospheric correction over the discrete bands from RSP measurements and the hyperspectral SPEX airborne measurements. The water-leaving signals determined this way are compared with both AERONET and Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color products for performance analysis. The results and lessons learned from this work will provide a basis to fully exploit the information from the unique combination of sensors on PACE for aerosol characterization and ocean ecosystem research.

Validation of GRASP algorithm product from POLDER/PARASOL data and assessment of multi-angular polarimetry potential for aerosol monitoring

“…The PARASOL/GRASP Optimized, HP and Models products are publicly available on the official GRASP algorithm website (https://www.grasp-open.com/products, last access: 28 March 2020) and at the AERIS/ICARE Data and Services Center (http://www.icare.univ-lille.fr, last access: 16 October 2018). The dataset used in the current study is registered under http://doi.org/10.5281/zenodo.3887265 (Chen et al, 2020).…”

Analysis of simultaneous aerosol and ocean glint retrieval using multi-angle observations

“…There is a rich literature describing MISR's technical characteristics (e.g., Bruegge et al, 1998Bruegge et al, , 2002Bruegge et al, , 2004Diner et al, 1998) and retrieval algorithms (e.g., Diner et al, 2005;Kahn et al, 2005a;Witek et al, 2019;Garay et al, 2020), so our description is limited to brief details relevant to this study.…”

“…This assumption has a long history in the ocean color remote sensing community (e.g., Gordon and Wang, 1994) and is appropriate for most of the open ocean. It is also assumed to be the case for both the red and NIR channels in the most recent operational MISR aerosol retrieval algorithm, V23 (Garay et al, 2020). Treatment of turbid or coastal water bodies would require a more extensive parameter space that we will not address in this work.…”

“…These instruments are capable, to varying degrees, of observing the atmospheric and oceanic state using their channels at visible (VIS) and near-infrared (NIR) wavelengths. For example, these observations can be used to identify and characterize suspended particles in the atmosphere (aerosols; e.g., Remer et al, 2005;Sayer et al, 2012;Witek et al, 2019;Garay et al, 2020), hydrosols in the ocean (representing suspended sediment or phytoplankton; e.g., Mobley et al, 2016;Werdell et al, 2013), or trace gas absorption in the atmosphere and pigment absorption in the ocean. In many cases, retrieval of aerosol and ocean geophysical parameters for observations over the ocean requires algorithms that account for both, by simultaneously determining those parameters, approximating their contribution to the observations, or selectively using observations that are minimally impacted by one or the other.…”

The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign

“…Airborne measurements of particulate backscatter and extinction have been important for assessing CALIOP 532 nm (Powell et al, 2009;Rogers et al, 2011) and 1064 nm (Vaughan et al, 2010(Vaughan et al, , 2019 level 1 attenuated backscatter profiles, level 2 aerosol optical depth (AOD) retrievals (Rogers et al, 2014), aerosol classification methodology (Burton et al, 2013), cirrus cloud properties (Yorks et al, 2011), and combined active (CALIOP) passive (Moderate Resolution Imaging Spectroradiometer, MODIS) retrievals of aerosol extinction profiles (Burton et al, 2010). Using airborne measurements to evaluate CALIOP aerosol backscatter measurements avoids uncertainties caused by systematic errors, spatial inhomogeneities, and distortions associated with using ground-based lidar measurements for such validation (Gimmestad et al, 2017). Consequently, ACEPOL also collected measurements under the CALIOP on flights conducted on 26 October and 7 and 9 November and under the CATS sensor on 19 October.…”