ProVal: A New Autonomous Profiling Float for High Quality Radiometric Measurements

Abstract

An efficient system to produce in situ high quality radiometric measurements is compulsory to rigorously perform the vicarious calibration of satellite sensors dedicated to Ocean Color Radiometry (OCR) and to validate their derived products. This requirement is especially needed during the early stages of an OCR satellite activity or for remote areas poorly covered by oceanographic cruises with possible bio-optical anomalies. Taking advantage of Argo's profiling float technology, we present a new autonomous profiling float dedicated to in situ radiometric measurements. The float is based on the Provor CTS5 (manufacturer NKE) with an added novel two protruding arm design allowing for sensor redundancies, shading mitigation and near-surface data. Equipped with two identical radiometers on each arm that measure downward irradiance and upwelling radiance at seven wavelengths, the ProVal float generates both redundant radiometric profiles as well as an estimate of Remote Sensing Reflectance. Results from 449 profiles obtained in the NW Mediterranean Sea and in the Indian sector of the Southern Ocean are presented to illustrate the ProVal float technical maturity. Analysis of the behavior of the profiling float, including tilting and ascent speeds is presented. The vertical stability of the ProVal exhibits 85% of surface data of the Mediterranean Sea with a tilt smaller than 10 degrees. This percentage is 40% in the Southern Ocean due to rougher seas. Redundant sensors provide a characterization of the relative drift between sensors over the deployment which is found to be <0.15% per month over a year. Post-cruise calibration of a recovered float revealed no significant drift. As an example of the utility of ProVal floats, a match-up of Remote Sensing Reflectance measured with the European Space Agency Ocean and Land Color Imager (OLCI onboard Sentinel-3A) is shown. It follows that profiling floats, such as ProVal, could provide a significant contribution to an upcoming global System Vicarious Calibration of space-based radiometers.

Merging bio-optical data from Biogeochemical-Argo floats and models in marine biogeochemistry

“…7a). Such findings were already established in Mignot et al (2014), indicating that the DCM is located at a fixed PAR value, oscillating near the 5.8 µmol photons m −2 s −1 isolume (Fig. 7b, blue line).…”

“…(b) Irradiance values (y axis) at DCM depth (x axis) for both modelled (red dot) and measured results (black dot). Horizontal blue line marks the 5.8 irradiance threshold (units µmol photons m −2 s −1 ) as identified in Mignot et al (2014). is positive if the model standard deviation is higher than the one from data results and negative in the opposite situation.…”

“…The introduction of BGC-Argo floats has led to a drastic increase in the number of radiometric measurements in the Mediterranean Sea, such as downward planar irradiance and photosynthetically available radiation (PAR), for which specifically developed quality control procedures and refined sensor calibration (Organelli et al, 2016a(Organelli et al, , 2017a have made their use widespread (Organelli et al, 2017b;Wojtasiewicz et al, 2018;Gerbi et al, 2016;Leymarie et al, 2018). BGC-Argo can therefore be an important source of high vertical spatial and temporal resolution data that can be integrated in the calibration and tuning of bio-optical numerical models for understanding marine biogeochemistry processes.…”

A BGC-Argo Guide: Planning, Deployment, Data Handling and Usage

“…Knowledge of the distribution of the in-water light field is therefore key to address the variability of such biogeochemical processes and understand their implications on the global carbon fluxes. In addition, radiometric measurements can be used to derive biogeochemical quantities such as chlorophyll and dissolved organic matter concentrations (e.g., Xing et al, 2011Xing et al, , 2012bOrganelli et al, 2017b) as well as being a fruitful data resource for ocean color satellite validation (Gerbi et al, 2016;Organelli et al, 2017a;Leymarie et al, 2018) and for improving predictions of numerical ecosystem models (Fujii et al, 2007;Terzić et al, 2019).…”

Satellite Ocean Colour: Current Status and Future Perspective

“…fleet is expected to expand, albeit not to the density of Argo, but with backscattering sensors (Dall'Olmo and Mork, 2014;Dall'Olmo et al, 2016;Organelli et al, 2017) and radiance sensors (Leymarie et al, 2018;Wojtasiewicz et al, 2018), which will enable greater understanding of the biogeochemical structure and possibly additional data for sensor validation. Furthermore, additional sensors could provide observations on biological diversity (Boss et al, 2018).…”