A Feasible Calibration Method for Type 1 Open Ocean Water LiDAR Data Based on Bio-Optical Models

Abstract

Accurate calibration of oceanic LiDAR signals is essential for the accurate retrieval of ocean optical properties. Nowadays, there are many methods for aerosol LiDAR calibration, but fewer attempts have been made to implement specific calibration methods for oceanic LiDAR. Oceanic LiDAR often has higher vertical resolution, needs greater signal dynamic range, detects several orders of magnitude lower less depth of penetration, and suffers from the effects of the air-sea interface. Therefore the calibration methods for aerosol LiDAR may not be useful for oceanic LiDAR. In this paper, we present a new simple and feasible approach for oceanic LiDAR calibration via comparison of LiDAR backscatter against calculated scatter based on iteratively bio-optical models in clear, open ocean, Type 1 water. Compared with current aerosol LiDAR calibration methods, it particularly considers geometric losses and attenuation occurring in the atmosphere-sea interface. The mean relative error percentage (MREP) of LiDAR calibration constant at two different stations was all within 0.08%. The MREP between LiDAR-retrieved backscatter, chlorophyll after using LiDAR calibration constant with inversion results of measured data were within 0.18% and 1.39%, respectively. These findings indicate that the bio-optical methods for LiDAR calibration in clear ocean water are feasible and effective.

Regional Models for High-Resolution Retrieval of Chlorophyll a and TSM Concentrations in the Gorky Reservoir by Sentinel-2 Imagery

“…To automate measurements, LiDAR systems are widely used in practical oceanology as express methods for assessing water quality [47][48][49][50][51]. They provided a high spatial resolution and a satisfied accuracy (according to some sources, like [52,79], the measurement error lies within 5-16%).…”

Remote Sensing Systems for Ocean: A Review (Part 2: Active Systems)

“…Lacour et al [249] used ARGO float measurements to evaluate CALIOP observations in North Atlantic. Moreover, Chen et al [267] deployed scattering values of bio-optical models for oceans to calibrate the oceanic LiDAR signals. They also proposed the optimal wavelengths for coastal water and open ocean studies.…”

LiDAR Remote Sensing for Vertical Distribution of Seawater Optical Properties and Chlorophyll-a From the East China Sea to the South China Sea

“…At each station, inherent optical properties (IOPs) were measured over depths ranging from 0 to 60 m using an absorption and attenuation meter (AC-S, Wetlab Ltd., America) and a backscatter meter (Hydroscat-6, HOBILabs Ltd., America). Chlorophyll-a fluorescence was measured using a multiparameter water quality monitor (RBR XR-420, RBR Ltd., Canada), and the fluorescence data were calibrated to extract chlorophyll-a concentration using a laboratory scanning spectrofluorometer (Trilogy, Turner Designs Inc.) [33]. The diffuse attenuation coefficient 𝐾 𝑑 was calculated by absorption and backscattering coefficients based on the Lee's model [34].…”

“…A hybrid retrieval method [15,26] was proposed to estimate the lidar extinction coefficient 𝑘 lidar and the backscatter coefficient at 180 degrees 𝛽 𝜋 (𝑧) based on the integration of the Klett retrieval method [36] and the perturbation retrieval (PR) method [17]. The lidar measured signal was calibrated by an iterative method [33].The Klett method assumes that there is a relationship between 𝑘 lidar (𝑧) and 𝛽 𝜋 (𝑧), and the PR method assumes that the water optical parameters can be expressed as the sum of a part that does not vary with depth 𝑆 ℎ (𝑧) and a varying part. Then, the 𝑘 lidar (𝑧) , 𝛽 𝜋 (𝑧) , and 𝑏 𝑏𝑏𝑝 could be estimated:…”