New Ocean Subsurface Optical Properties From Space Lidars: CALIOP/CALIPSO and ATLAS/ICESat‐2

Abstract

Ocean color remote sensing entered a new era with the launch of the National Aeronautics and Space Administration (NASA) Coastal Zone Color Scanner in 1978 (C. W. Sullivan et al., 1993). For the first time, maps of phytoplankton biomass (chlorophyll)-a key measurement of marine ecosystems-could be produced from space-based observations, with the potential for daily to interannual observations at ocean basin scales. Regional to global maps of phytoplankton chlorophyll and other products derived from satellite measurements of water-leaving radiance are now accessible to users all over the world and have become an essential tool for the study and analysis of ocean biogeochemistry and ocean ecosystems. For decades, ocean color remote sensing has led to unprecedented scientific understanding in global ocean biology and biogeochemistry (Blondeau-Patissier et al., 2014;Brown et al., 1985;Dickey et al., 2006). However, because previous ocean color measurements have relied solely on passive remote sensing techniques, the data coverage is limited to the uppermost portion of the water column and is unable to resolve the underlying vertical structure (Hostetler et al., 2018;Jamet et al., 2019). Moreover, passive sensors (e.g., the MODerate-resolution Imaging Spectroradiometer, MODIS) only provide ocean color records during daytime. As a result, vast ocean areas in high latitudes during polar nights remain unsampled and places for which data are available typically provide information for only a few months in each calendar year.Estimates of global phytoplankton distributions from a space-based lidar were first demonstrated using measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) (Behrenfeld et al., 2013). CALIOP is a dual-wavelength (532 and 1,064 nm), polarization sensitive (at 532 nm) elastic backscatter lidar that has been making measurements from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite since June 2006(Hunt et al., 2009Winker et al., 2009). Using the CALIOP depolarization ratio measurements at 532 nm together with colocated A-Train measurements, such as Advanced Microwave Scanning Radiometer-Earth observing system (AMSR-E) wind speeds and MODIS diffuse attenuation coefficients (k d , m −1 ), innovative retrieval methods have been developed to translate the CALIOP ocean backscattered signals into ocean optical properties, such as the particulate backscatter coefficient (b bp , m −1 ) (

Validation of ICESat-2 Derived Data Products on Freshwater Lakes: Bathymetry, Diffuse Attenuation Coefficient for Downwelling Irradiance (Kd ), and Particulate Backscatter Coefficient (b bp)

“…Both K d and b bp are calculated using the method developed by [8], [20]. For the scope of this study, both K d and b bp refer to the metrics sampled at a wavelength of 532 nm.…”

Informing ocean color inversion products by seeding with ancillary observations

“…While these data have not been formally validated, they were considered by [40] to exhibit general agreement with MODIS-Aqua 𝑏 %& (532) retrievals. The product continues to be developed and refined [41]. We acquired Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) 𝑏 %& (532) daytime products from the Oregon State University Ocean Productivity group (http://orca.science.oregonstate.edu/lidar.data.php).…”

The use of spaceborne lidar to map Antarctic krill distributions and biomass in the Southern Ocean

“…As an active remote sensing technology, LiDAR has the advantages of high resolution, flexibility and efficiency (Renhe, 1994;Liu et al, 2015), and is capable of obtaining information on the vertical structure of phytoplankton and marine environmental factors, such as temperature, sea ice and chlorophyll, on a large scale and periodically (Sullivan et al, 2010;Behrenfeld et al, 2017;Chen and Pan, 2019;Yunfeng et al, 2020). Cloud aerosol lidar and infrared pathfinder satellite observations (CALIPSO) launched by NASA provides imagery that supports the characterization of the vertical structure of plankton near the ocean surface (Lu et al, 2021). The orthogonally polarized cloud aerosol lidar (CALIOP) carried on CALIPSO is the first dual-polarized lidar to provide a global vertical profile of diurnal elastic backscatter (Lu et al, 2014).…”