D. Antoine, E. Leymarie, A. Morel, B. Gentili Laboratoire d'Océanographie de Villefranche, France J.P. Buis, N. Buis, S. Victori, S. Meunier, M Canini CIMEL Electronique, Paris B. Fougnie, P. Henry CNES, Toulouse center, France Anisotropy of the underwater light field: development of a “radiance camera”

About minute acquisition sequences taken at 6Hz, of E s, E d, E u, and nadir L u, at z=4 & 9 meters Along with wave height, wave period, IOPs and AOPs. Paper submitted to JGR … waiting for Editor decision A data set that might be of interest to you in the frame of Radyo

Anisotropy of the underwater light field Characterized by the “Q factor”:Characterized by the “Q factor”: Q is rhe ratio between the upwelling irradiance (E u ) and the upwelling radiance (L u ) measured in a given direction. Q depends on :  The sun position  The observation direction  The wavelength  Water optical properties (IOPs)  Knowledge of this “Q factor” is important to accurately derive the marine reflectance from the satellite remote sensing measurement at the top of the atmosphere I.Introduction, context, background

Anisotropy of the underwater light field Q can be derived from RT Simulations (Morel & Gentili, 1991, 1993, 1996; Morel et al 2002)Q can be derived from RT Simulations (Morel & Gentili, 1991, 1993, 1996; Morel et al 2002) The accuracy of such simulations mostly derives from that of the VSF  These simulations are partly validated in open ocean “Case I waters”  Still no measurements in coastal “Case II waters”  nearly nothing for the downwelling hemisphere I.Introduction, context, background

II.The Radiance Camera Our general goal - Develop our own instrument - Tentatively improve some parts of the design as compared to existing instrumentation - Further describe the distribution of the upwelling radiance just beneath the sea surface (bio-optical state, sea state, atmospheric conditions) - Extend the description to various depths within the lit layers - Extend the description to Case 2 waters - Simultaneously measure the upwelling and downwelling hemispheres - Invert the full radiance distribution in terms of the VSF ?

II.The Radiance Camera Partnership and project history Mid 2002 : First discussion between LOV, CNES and CIMEL. Definition of specifications Definition of specifications 2003 : Project funded by a CNES “Research & Technology” action CIMEL : Conception (optic, electronic) and realization of the camera LOV : Science background, system specifications, characterization and validation of the prototype, deployment at sea 2006 : Additional funding from CNES 2008 : Test of the first prototype

Specifications of the camera Radiometric : - sensitivity better than Wm -2 nm -1 sr -1 - accuracy better than 5% - measurement range : to 1 Wm -2 nm -1 sr -1 - dynamic over 1 image : 3 decades - Multi-spectral in the visible range Geometric : - Hemispheric field of view (a bit larger actually) - angular resolution ~ 1° Specific : - integration time < 100 ms (movement caused by waves) - Longer integration times as well (very dim light) - compact design to minimize self-shading - highly resistant to blooming effect (image of the sun) II.The Radiance Camera

Schematic description Fish eye optic Bandpass filters (on a filter wheel) CMOS CMOS matrix Aux Auxiliary sensors Com Data transfer & commands 200m depth container 200m electrical/optical cable II.The Radiance Camera

Full description CMOS Aux Com The Fish Eye Optic :The Fish Eye Optic : ­Telecentric, non achromatic ­Developed specifically for this application ­Patented by CIMEL II.The Radiance Camera

Full description CMOS Aux Com Filters :Filters : ­The telecentric optic allows a small incidence angle on the filters ­Filters used in the camera (Semrock ®): λ (nm) Δ λ (nm) II.The Radiance Camera

Full description Sensor :Sensor : The choice of the sensor to have : dynamic, sensitivity and no blooming is a key point for this project CDD : Best sensitivity, subject to blooming CMOS : less sensitive, more linear, no blooming  Our Choice : a “commercial” CMOS, monochrome, 12 bit digitization, HD format (1920 x 1080), pixel size 5  m CMOS Aux Com  Main difficulty: trade off between specs, cost, availability II.The Radiance Camera

Full description Auxiliary sensors :Auxiliary sensors : ­Compass ­depth sensor ­tilt sensor ­Internal temperature and humidity CMOS Aux Com II.The Radiance Camera

Full description Data transferData transfer ­optical connection (CameraLink®) ­transfer rate : 15 frames/s (max) ­file : 2.3 Mo / frame, Tiff format Instrument commandsInstrument commands ­RS232 through CameraLink® CMOS Aux Com II.The Radiance Camera

The first prototype of the LOV-CIMEL Radiance Camera Camera delivered at the end of 2007 : Size (mm): Ø96 * 260 weight : 2.4 kg II.The Radiance Camera

Test of the deployment system, 14/03/08 Test in air The first prototype of the LOV-CIMEL Radiance Camera II.The Radiance Camera

III.Initial characterization results Villefranche Radiometry Facility 2 darkrooms at the Laboratoire d’Océanographie de Villefranche2 darkrooms at the Laboratoire d’Océanographie de Villefranche One optical table and large assortment of optomechanic componentsOne optical table and large assortment of optomechanic components 1000 W halogen calibrated Lamps and stabilized power supply1000 W halogen calibrated Lamps and stabilized power supply Large Spectralon® calibrated reflective targetLarge Spectralon® calibrated reflective target Irradiances and radiance calibrated sensorsIrradiances and radiance calibrated sensors

Angular resolution Comparison between 0 and 1° sight 6 images (different λ) Pinhole Convex Lens f Beam div. < 0.5° III.Initial characterization results

Angular resolution 0° sight III.Initial characterization results

1° 6 images (different λ) sum 6 images (different λ) Angular resolution Comparison between 0 and 1° sight 0° 6 images (different λ) III.Initial characterization results

Angular resolution Comparison between 0 and 1° sight  Angular resolution better than 1° III.Initial characterization results

 Correspondence between a direction in space and a position on the imager, in theory : θ = k.r (where r is the distance to the center) Rotation 5° step Estimation of the distance r(θ,λ) from peak to center Geometric characterization III.Initial characterization results

Geometric characterization  Link between a direction and a position on the imager In theory : θ = k.r (where r is the distance to the center) III.Initial characterization results

Geometric characterization  Link between a direction and a position on the imager III.Initial characterization results

Geometric characterization  Link between a direction and a position on the imager  Field of view = ± 92° III.Initial characterization results

 Experimental Setup Spectralon® target d View of the camera Sensitivity (S/N at low radiance) III.Initial characterization results

 Estimation of radiance range to measure (upwelling flux) Wm ‑ 2 nm ‑ 1 sr ‑ 1 Depth : 0- λminmax 412 nm5.E-045.E nm5.E-045.E nm5.E-052.E-02  Estimation of radiance intensity with our setup radiance (Wm ‑ 2 nm ‑ 1 sr ‑ 1 ) 406 nm438 nm494 nm560 nm628 nm 5.40E E E E E-03 Sensitivity (S/N at low radiance)  We are in low radiance configuration at 406nm III.Initial characterization results

Sensitivity (S/N at low radiance)  Methodology : 1.Acquisition of 20 images, for each λ, exposure 100 ms 2.Extraction of 16 pixels (4*4 square) in the middle of the target 3.Calculating of ΔCount for 1 pixel over 20 images. Gives S/N (1 pixel) 4.Calculating of ΔCount for 16 pixels over 20 images. Gives S/N (16 pixels) 406 nm438 nm494 nm560 nm628 nm S/N (1 pixel) S/N (16 pixels) III.Initial characterization results

Rolloff of the fish-eye optics  Definition : Rolloff of a lens is the attenuation of radiance on increase in view angle. It depends on : Optic’s attenuation Variation of dΩ view by each pixel Plaque Spectralon d III.Initial characterization results

Spectralon® target d Rolloff of the fish-eye optics III.Initial characterization results

L θ 90°-90° Rolloff of the fish-eye optics III.Initial characterization results

Rolloff of the fish-eye optics III.Initial characterization results

Q factor measurement IV.Preliminary field results Q Measurement: Cruise : “SORTIE” Date : 17 oct 2008 – 13h30 UT Location: BOUSSOLE Sun Zenith : 61.2° - Blue Sky 560nm, integration time : 90ms “SORTIE” cruise: PI C. Trees, 2 weeks in October 2008 in the Mediterranean Sea Q

Q nadir comparison IV.Preliminary field results Q comparison: Cruise : NATO Date : 26 oct 2008 – 13h30 UT Place : SW Pisa Sun Zenith : 61° - Blue Sky “SORTIE” cruise: PI C. Trees, 2 weeks in October 2008 in the Mediterranean Sea Qnadir comparisons between the camera and SAtlantic’s free fall profilers

Q factor comparison IV.Preliminary field results Q comparison: Cruise : Optic-Med Date : 5,7 and 8 Mai 2008 Place : Mediterranean sea Blue Sky, coastal blue waters [Chla] : mg.m -3 “Optic-Med” cruise: 2 weeks in April 2008, in the Mediterranean Sea Qnadir comparisons between the camera and the Morel&Gentili Model 1:1

Thank you for your attention

Measurements of the in-water radiance field History : Univ. Miami, RSMASHistory : Univ. Miami, RSMAS ­Ken Voss 1988 –> present : Fish Eye camera coupled with a CID (then a CCD) matrix and spectral filters Voss et al, 2007, Biogeosciences I.Introduction, context, background

BOUSSOLE-AOPEX cruise, 08/1/2004 Measurements of the in-water radiance field History :History : ­K. Voss 1988 – present : Fish Eye camera with CID (then CCD) matrix and wavelength bandpass filters Model Data Q nadir at 486 nm K. Voss et al. (2007) I.Introduction, context, background

Evolution of the internal temperature III.Initial characterization results