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Titolo:
Offshore tower shading effects on in-water optical measurements
Autore:
Zibordi, G; Doyle, JP; Hooker, SB;
Indirizzi:
Commiss European Communities, Joint Res Ctr, Space Applicat Inst, Marine Environm Unit, I-21020 Ispra, VA, Italy Commiss European Communities Ispra VA Italy I-21020 1020 Ispra, VA, Italy Univ London Imperial Coll Sci Technol & Med, Environm Technol Ctr, Dept Phys, London, England Univ London Imperial Coll Sci Technol & Med London England don, England NASA, Goddard Space Flight Ctr, Lab Hydrospher Proc, Greenbelt, MD 20771 USA NASA Greenbelt MD USA 20771 Lab Hydrospher Proc, Greenbelt, MD 20771 USA
Titolo Testata:
JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY
fascicolo: 11, volume: 16, anno: 1999,
parte:, 2
pagine: 1767 - 1779
SICI:
0739-0572(199911)16:11<1767:OTSEOI>2.0.ZU;2-G
Fonte:
ISI
Lingua:
ENG
Soggetto:
IRRADIANCE MEASUREMENTS; SIMULATIONS; OCEAN;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
28
Recensione:
Indirizzi per estratti:
Indirizzo: Zibordi, G Joint Res Ctr, Inst Delle Appl Spaziali, SAI-TP 272, I-21020 Ispra, VA, Italy Joint Res Ctr SAI-TP 272 Ispra VA Italy I-21020 spra, VA, Italy
Citazione:
G. Zibordi et al., "Offshore tower shading effects on in-water optical measurements", J ATMOSP OC, 16(11), 1999, pp. 1767-1779

Abstract

A field campaign was performed to estimate the shading effect induced on in-water irradiance and radiance measurements taken in the immediate vicinity of the Acqua Alta Oceanographic Tower (AAOT), located in the northern Adriatic Sea, which is regularly used to support ocean color validation activities; Sequences of downwelling irradiance and upwelling radiance profiles were collected at varying distances from the tower to evaluate the shading effects during clear-sky conditions as a function of the deployment distance. The experimental data, as well as Monte Carlo simulations, indicate that the shading effect is negligible for both downwelling irradiances and upwelling radiances at deployment distances greater than 15 and 20 m, respectively. At closer distances, for example, at the 7.5-m deployment distance regularly used at the AAOT for the collection of underwater optical measurements, the shading effect is remarkable: both field and simulated data at a depth of 7 m and a wavelength of 443 nm show that, with a relatively low sun zenith angle of 22 degrees, the shading effect is within 3% for downwelling irradiance and within 8% for upwelling radiance. Monte Carlo simulations at443, 555, and 665 nm, computed at a depth of 0(-) m and with values of seawater inherent optical properties representative of the AAOT site, are usedto extend considerations on shading effects to measurements taken during different illumination conditions at the 7.5-m deployment distance. Simulations for ideal clear-sky conditions (i.e., in the absence of atmospheric aerosols) show that errors induced by AAOT perturbations significantly vary asa function of wavelength and sun zenith angle. The highest values are observed at 443 nm where, with the sun zenith angle ranging from 20 degrees to 70 degrees, errors vary from 2.4% to approximately 6.2% for downwelling irradiance and from a minimum of 3.0% (occurring at 30 degrees) to almost 6.6%for upwelling radiance. Simulations also show that thr shading error can be as high as approximately 20% for both irradiance and radiance measurements taken during overcast sky conditions.

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Documento generato il 23/09/20 alle ore 21:03:35