Effects of integration time on in-water radiometric profiles

This work investigates the effects of integration time on in-water downward irradiance Ed, upward irradiance Eu and upwelling radiance Lu profile data acquired with free-fall hyperspectral systems. Analyzed quantities are the subsurface value and the diffuse attenuation coefficient derived by applying linear and non-linear regression schemes. Case studies include oligotrophic waters (Case-1), as well as waters dominated by Colored Dissolved Organic Matter (CDOM) and Non-Algal Particles (NAP). Assuming a 24-bit digitization, measurements resulting from the accumulation of photons over integration times varying between 8 and 2048 ms are evaluated at depths corresponding to: 1) the beginning of each integration interval (FST); 2) the end of each integration interval (LST); 3) the averages of FST and LST values (AVG); and finally 4) the values weighted accounting for the diffuse attenuation coefficient of water (WGT). Statistical figures show that the effects of integration time can bias results up to 5% as a function of the depth definition. Examples are provided by Eu and Lu data products obtained with FST or LST depths when the optical system is deployed faster than 0.4 ms-1 in CDOM-dominated waters. The study also documents that perturbations due to the light focusing of sea-surface facets can oppositely affect biases due to the time integration and the log-transformation applied to determine data products with the linear regression scheme. Results indicate the validity of the WGT scheme and the fair applicability of the AVG. Instead, both the FST and LST schemes should not be adopted since they may introduce pronounced biases in Eu and Lu data products for highly absorbing waters.

D'ALIMONTE Davide;  ZIBORDI Giuseppe;  KAJIYAMA Tamito; 

2018-03-26

OPTICAL SOC AMER

JRC108309

1094-4087,   

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-5908,    https://publications.jrc.ec.europa.eu/repository/handle/JRC108309,   

10.1364/OE.26.005908.,