In situ evaluation of spaceborne CALIOP lidar measurements of the upper-ocean particle backscattering coefficient.

Léo Lacour,Marcel Babin,Raphael Larouche

doi:10.1364/oe.397126

Abstract

The spaceborne CALIOP lidar, initially designed for atmospheric measurements, was recently used to retrieve the particulate backscattering coefficient (bbp) in ocean subsurface layers. However, extensive field evaluation of CALIOP estimates was never conducted due to the scarcity of in situ data. Here, year-round and basin-wide data from Biogeochemical Argo floats (BGC Argo) were used to evaluate CALIOP estimates in the North Atlantic. The high density of BGC Argo float profiles in this region allowed us to test different matchup strategies at different spatio-temporal scales. When averaged over 2° by 2° grid boxes and monthly time resolution, CALIOP data present reasonably good correlation with highly variable float bbp values (correlation r = 0.44, root mean square relative error RMS% = 13.2%), suggesting that seasonal dynamics can be characterized at basin scale.

Highlights

The National Aeronautics and Space Administration (NASA) and the Centre National d’Etudes Spatiales launched in 2006 the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite [1]
While good-quality estimates were retrieved for 65% of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) shots at global scale in Behrenfeld et al [3], we could only use 10% of total CALIOP shots in the North Atlantic subpolar ocean, using the same quality-control procedure
The recent development of the BGC-Argo float network provided a new opportunity to evaluate CALIOP bbp estimates over a complete annual cycle and on a basin scale

Summary

Introduction

The National Aeronautics and Space Administration (NASA) and the Centre National d’Etudes Spatiales launched in 2006 the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite [1]. CALIOP subsurface measurements provide estimates of the backscattering coefficient of suspended particles (bbp(λ), m−1) from which phytoplankton biomass or particulate organic carbon can be derived [3] These active lidar measurements can be conducted both day and night, at low solar elevations and through considerable aerosol loads and thin clouds, palliating many limitations of passive ocean color remote sensing, in polar and subpolar regions [7,8]. Only one study from Behrenfeld et al [3] conducted a comparison analysis between CALIOP subsurface bbp retrievals and in situ data They used ship-based bbp data collected during the 2012 AMT22 cruise in the North Atlantic between 15 (45°N, 20°W) and 24 October (22°N, 40°W). The CALIOP bbp data could not be evaluated over the full seasonal cycle

Methods

Results

Conclusion