Airborne lidar surveys were used to characterize subsurface layers of phytoplankton in the Arctic Ocean during the latter half of July 2014 and again during the latter half of July 2017. The survey region included US waters in the Beaufort and Chukchi Seas. In 2014, layers were detected in open water and also in openings in pack ice where up to 90% of the surface was covered by ice. The layers in the pack ice were less prevalent, weaker, and shallower than those in open water. Layers were more prevalent in the Chukchi Sea than in the Beaufort Sea. Three quarters of the layers observed were thinner than 5 m. In 2017, ice conditions were significantly different. The ice edge was farther north at the beginning of the measurement period in 2017 and retreated faster during that period. As a result, flights were conducted in the areas surveyed in 2014 in addition to areas near the ice edge. Data analysis of the 2017 flights will be done in the same way as the 2014 data. Low clouds and fog are common in the Arctic. The lidar can operate through optically thin clouds and fog, but at some point, the beam is completely attenuated. Data where the atmospheric attenuation is too great must be removed from consideration by visual inspection. Detection of ice in the lidar return is straightforward, since ice produces a saturated return in the lidar receiver. Subsurface layers will be identified by visual inspection of the data, and the characteristics will be calculated. Subsurface layers are clearly present in the data, and their characteristics will be presented, along with a comparison between 2014 and 2017 results.

The backscattering coefficient of seawater, defined as the coefficient of scattering at angles > 90 degrees, includes contributions from water and from any particles in the water. The water contribution has a relatively narrow range of values in the ocean, but the particulate contribution depends on the number of particles in the water and their type. Measurements of the particulate backscattering coefficient generally take advantage of the relatively small variability in scattering with angle at angles > 90 degrees to obtain an estimate of the backscattering coefficient from scattering at a single angle. Lidar has been used to infer the backscattering coefficient from scattering at 180 degrees, but this depends on knowledge of the relationship between scattering at this angle and the backscattering coefficient. It also depends on an absolute radiometric calibration, although this can be avoided using high-spectral-resolution lidar. Here, we consider a technique to obtain the backscattering coefficient directly from lidar data by calibration against passive ocean color measurements. The technique does not depend on retrieval of either the lidar calibration coefficient or the relationship between the volume scattering function at 180 degrees and the backscattering coefficient, but can be used to infer both quantities. The only requirement is that the relationship between the scattering parameters not change significantly over the area, depth range, or duration of the measurements. Once the relationship is found, it can be used where the satellite measurements are affected by clouds or vertical structure in the scattering.