Shipborne oceanic high-spectral-resolution lidar for accurate estimation of seawater depth-resolved optical properties

Abstract

Lidar techniques present a distinctive ability to resolve vertical structure of optical properties within the upper water column at both day- and night-time. However, accuracy challenges remain for existing lidar instruments due to the ill-posed nature of elastic backscatter lidar retrievals and multiple scattering. Here we demonstrate the high performance of, to the best of our knowledge, the first shipborne oceanic high-spectral-resolution lidar (HSRL) and illustrate a multiple scattering correction algorithm to rigorously address the above challenges in estimating the depth-resolved diffuse attenuation coefficient Kd and the particulate backscattering coefficient bbp at 532 nm. HSRL data were collected during day- and night-time within the coastal areas of East China Sea and South China Sea, which are connected by the Taiwan Strait. Results include vertical profiles from open ocean waters to moderate turbid waters and first lidar continuous observation of diel vertical distribution of thin layers at a fixed station. The root-mean-square relative differences between the HSRL and coincident in situ measurements are 5.6% and 9.1% for Kd and bbp, respectively, corresponding to an improvement of 2.7–13.5 and 4.9–44.1 times, respectively, with respect to elastic backscatter lidar methods. Shipborne oceanic HSRLs with high performance are expected to be of paramount importance for the construction of 3D map of ocean ecosystem.

Potential of Mie–Fluorescence–Raman Lidar to Profile Chlorophyll a Concentration in Inland Waters

“…Meanwhile, some biases should be noted. In April 2021, there were relatively obvious overestimations of approximately 4.7 μg/L with RMSRD of 29.6% at station S1 and of approximately 2.2 μg/L with RMSRD of 29.5% at station S2, which may be due to the overestimation of K d caused by multiple scattering effects on lidar retrieval . In July 2021, there were general underestimations at the peaks of Chl -a profiles at stations S3, S4, and S5 with RMSRD values of 17.5, 11.2, and 22.3%, respectively.…”

“…Herein, the correlation of Chl -a concentration between ZJU-MFRL and in situ measurements was a little better than most of those ranging from −0.13 to 0.96 from the NOAA (National Oceanic and Atmospheric Administration) airborne lidar system. The difference may be due to the spatial and temporal gaps between the airborne lidar and water sampling that cause different measured waters, , which can be almost ignored here since ZJU-MFRL and in situ measurements worked on the shipboard simultaneously. Furthermore, the combined use of Mie, fluorescence, and Raman channels supplements the insufficient optical information on Mie Signal and the rapid decay of Raman and fluorescence signals, evolving current applications of elastic lidar and enabling the quantitative vertical observations and further cooperation with other synchronous technologies. , …”

“…Lidar, a burgeoning active optical remote sensing technique, − can penetrate the water – air interface and provide continuous vertical phytoplankton information on the upper water column to three optical depths with high spatial–temporal resolution. ,, Lidar technology has been used successfully in marine biogeochemistry research based on empirical bio-optical model. − However, this model was established by using in situ data from ocean cruises and focused on Case 1 water, which is a two-component system consisting of water and a biological compartment. Consequently, it cannot be directly applied to inland waters.…”

Validation protocol for the evaluation of space-borne lidar particulate back-scattering coefficient bbp

“…Recent developments of shipborne lidar confirmed the potential of lidar to monitor the scattering and phytoplankton layers over the first tens of meters (Collister et al, 2018;Zimmerman et al, 2020;Shen et al, 2022;Zhang et al, 2022). Although airborne and shipborne lidar sensors were shown to have great potential for measuring the optical properties of the water column for various applications (Steinvall and Björck, 2020;Zhou et al, 2022), there are currently no space-borne lidars designed specifically for this purpose. Nevertheless, there have been studies that have utilized data from the CALIOP and ATLAS sensors aboard CALIPSO and ICESat-2 satellite respectively, which were not initially intended for ocean applications (Behrenfeld et al, 2013;Behrenfeld et al, 2017;Lu et al, 2014;Lu et al, 2016;Hostetler et al, 2018;Lu et al, 2022).…”

Decoupling and Parameter Extraction Methods for Conical Micro-Motion Object Based on FMCW Lidar

“…At present, high-resolution lidar measurement technology plays an important role in fields such as ocean exploration [ 1 ] and atmospheric environment monitoring [ 2 ]. Laser micro-Doppler technology, as one of the high-resolution measurement methods, has been widely used in various fields such as vital sign detection [ 3 , 4 , 5 , 6 ], drone detection [ 7 , 8 ], automotive radar detection [ 9 ], vibration measurement [ 10 ], and bird recognition [ 11 ].…”