profile. Airborne lidar observations are in-between. The aircraft can cover a large area and our goal for the project was to understand the spatial variability of the bubble clouds at high resolution between the lidar profiles and around the fixed echo sounder profiles.’

From the sea to space Existing oceanographic lidars are relatively large and expensive airborne systems, said Collister, which the ocean science community has limited access to. As such, the Old Dominion University team designed a relatively inexpensive and compact ship-borne lidar system. It measures profiles of lidar attenuation and depolarisation simultaneously with in-water measurements of particle optical and biogeochemical properties. Collister said that it helps ‘improve our models and develop new understanding of how the laser light interacts with the particles. ‘One of the more interesting things that

we are seeing with this new instrument is that lidar measurements of depolarisation have the potential to give us information

Leica Chiroptera 4X integrates a topographic lidar, a bathymetric lidar and a red-green-blue-near-infrared camera

on the types of particles in the water, not just their concentration,’ he said. ‘This could allow us to better parameterise the role of particles in models of ocean chemistry.’ The Old Dominion team is currently

developing a commercial instrument that will be smaller, lighter and provide greater depth penetration and vertical resolution. ‘The portability of this system allows us to move it from vessel to vessel, and even deploy it beneath the water

to increase the depth range,’ Collister said. This is beneficial because it can be challenging to validate oceanographic lidar measurements made from air- and spaceborne instruments against ‘in-water measurements that oceanographers really care about,’ he added. ‘The number of matchups between lidar and in-water measurements that we can achieve with this system is unprecedented, and will allow us to rapidly develop lidar techniques that can be scaled up to air- and spaceborne instruments.’ While small systems are convenient,

Schulien is keen to see more lidar instruments launched into space. ‘The ability to measure depth-resolved bbp, Kd and depolarisation night and day has implications for so many different areas of research,’ she said. ‘My current research is focused on fish foraging ecology. If an instrument like the HSRL were launched on a satellite, these data could be used for studying fish and could additionally provide valuable data for different areas of ecology-based research.’ However, it’s not yet clear when that hope might be realised. Such an instrument is not yet planned

for a Nasa mission, but researchers are pushing to include it in a European Space Agency payload, Schulien said. For now, Nasa’s Plankton, Aerosol, Cloud, ocean Ecosystem (Pace) mission, to launch next year, will include two passive polarimeters, which are dependent on sunlight, taking a step in that direction. ‘Even though it’s not from an active

Leica Hawkeye 4X adds another bathymetric lidar designed to collect data from greater depths

16 Electro Optics June 2021

sensor, I’m really excited about the potential for informing phytoplankton research,’ said Schulien. EO

@electrooptics |



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