Ocean lidar measurements of beam attenuation and a roadmap to accurate phytoplankton biomass estimates

Yongxiang Hu (1) , Mike Behrenfeld (2) , Chris Hostetler (1) , Jacques Pelon (3) , Charles Trepte (1) , Johnathan Hair (1) , Wayne Slade (4) , Ivona Cetinic (5) , Mark Vaughan (1) , Xiaomei Lu (1) , Pengwang Zhai (6) , Carl Weimer (7) , David M. Winker (1) , Carolus C. Verhappen (1) , Carolyn Butler (1) , Zhaoyan Liu (8) , Bill Hunt (1) , Ali Omar (1) , Sharon Rodier (1) , Anne Lifermann (2) , Damien Josset (9) , Weilin Hou (9) , David Macdonnell (1) , Ray Rhew (1)

1 LaRC - NASA Langley Research Center [Hampton]
2 OSU - Oregon State University
3 TROPO - LATMOS
4 Sequoia Scientific Inc.
5 University of Maine
6 UMBC - University of Maryland [Baltimore County]
7 Ball Aerospace and Technologies Corp.
8 NIA - National Institute of Aerospace [Hampton]
9 NRL - Naval Research Laboratory

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30° off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Ecosystèmes

Yongxiang Hu, Mike Behrenfeld, Chris Hostetler, Jacques Pelon, Charles Trepte, et al.. Ocean lidar measurements of beam attenuation and a roadmap to accurate phytoplankton biomass estimates. EPJ Web of Conferences, 2016, The 27th International Laser Radar Conference (ILRC 27), 119, pp.22003. ⟨10.1051/epjconf/201611922003⟩. ⟨insu-01176027⟩