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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-373
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
26 Jan 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
Autonomous marine hyperspectral radiometers for determining solar irradiances and aerosol optical properties
John Wood1, Tim J. Smyth2, and Victor Estellés3 1Peak Design Ltd, Sunnybank House, Wensley Rd, Winster, Derbys. DE4 2DH UK
2Plymouth Marine Laboratory, Prospect Place, Plymouth, Devon, PL1 3DH, UK
3Dept. Física de la Terra i Termodinàmica, Universitat de València, Burjassot, 46100, Spain
Abstract. We have developed two hyperspectral radiometer systems which require no moving parts, shade rings or motorised tracking making them ideally suited for autonomous use in the inhospitable remote marine environment. Both systems are able to measure the direct and diffuse hyperspectral irradiance fields in the wavelength range 350–1050 nm at 6 nm (Spectrometer 1) or 3.5 nm (Spectrometer 2) resolution. Marine field-trials along a 100° transect (between 50° N and 50° S) of the Atlantic Ocean resulted in close agreement with existing commercially available instruments in measuring: (1) photosynthetically available radiation (PAR) with both spectrometers giving regression slopes close to unity (Spectrometer 1: 0.960; Spectrometer 2: 1.006) and R2 ~ 0.96; (2) irradiant energy, with R2 ~ 0.98 and a regression slope of 0.75 which can be accounted for by the difference in wavelength integration range and; (3) hyperspectral irradiance where the agreement on average was between 2–5 %. Two long duration land based field campaigns of up to 18 months allowed both spectrometers to be well calibrated. This was also invaluable for empirically correcting for the wider field-of-view (FOV) of the spectrometers in comparison with the current generation of sun photometers (~ 7.5° compared with ~ 1°). The need for this correction was also confirmed and independently quantified by atmospheric radiative transfer modelling and found to be a function of aerosol optical depth (AOD) and solar zenith angle. Once Spectrometer 2 was well calibrated and the FOV effect corrected for, the RMSE in retrievals of AOD when compared with a CIMEL sun photometer were reduced to ~ 0.02–0.03 with R2 > 0.95 at wavelengths 440, 500, 670 and 870 nm. Corrections for the FOV as well as ship motion were applied to the data from the marine field trials. This resulted in AOD500 nm ranging between 0.05 in the clear background marine aerosol regions to ~ 0.5 within the Saharan dust plume. The RMSE between the handheld Microtops sun photometer and Spectrometer 2 was between 0.047–0.057 with R2 > 0.94.

Citation: Wood, J., Smyth, T. J., and Estellés, V.: Autonomous marine hyperspectral radiometers for determining solar irradiances and aerosol optical properties, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-373, in review, 2017.
John Wood et al.
John Wood et al.
John Wood et al.

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Short summary
We have developed an instrument which can be deployed on ships in the remote oceans to measure optical properties of the atmosphere. These optical properties are key to understanding how light and heat are transmitted, absorbed and reflected within the atmosphere. This has consequences for how the wider climate system works. The oceans, covering 70 % of the planet, are chronically undersampled for such optical properties. Such instruments, when widely deployed, should help rectify this problem.
We have developed an instrument which can be deployed on ships in the remote oceans to measure...
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