Quantification of mineral particles from remote sensing. Using of spectroradiometric measurements and WASI simulations

Transcription

1 Quantification of mineral particles from remote sensing. Using of spectroradiometric measurements and WASI simulations Results obtained by V. Lafon, C. Giry, N. Bonneton, D. Doxaran, D. Bru C. Petus, M. Schmeltz and J-M Froidefond 1) Spectroradiometric measurements 2) Examples of SPMC quantification in the Bay of Biscay, the French Guiana and the Congo coastal waters 3) Inversion of spectra from the WASI code (P. Gege)

2 Spectroradiometric measurements Irradiance measurement with a Trios sensor (E d ). 350nm 950nm Calibrations in air before or after the survey at Trios Remote sensing reflectance R rs ( ) 0.98* L (0, ) E (0, ) u d Radiance measurements with Trios sensors located above + 2cm and below -2cm (L u ). ± 1cm Froidefond and Ouillon, 2005

3 Example of reflectance spectra (R rs (l) Irradiance (E d ) Water radiance (L u ) Remote sensing reflectance Rrs(l) Rrs(sr -1 ) = L u /E d

4 Clear waters Water radiance just below the sea surface Shadow effects relatively low Water radiance just above the sea surface Turbid waters (> 30mg/L) Very high shaddow effects Backscattered light attenuated by the shadow of the sensor Radiance measured above the sea surface

5 Identification and quantification of suspended particles Bay of Biscay (SHOM, INSU, Region) Optic-Med (SHOM) French Guiana (IRD, PNEC Bissecotte (IRD) Optic-Congo (SHOM) About 400 spectra recorded during different oceanographic surveys in case 2 waters. At each station, hydrologic data (SPM, CDOM, Chlorophyll-a or fluorescence, CDOM Gironde area : quantification of mineral particles (PNEC) Arcachon area (CNES, Kalideos-Littoral) Intertidal and subtidal mapping Gironde area Arcachon area Adour area Adour area : OOSEA program Remote sensing monitoring in Aquitaine Euskadi (AZTI, LASAGEC, EPOC)

6 Différent types of reflectance spectra Reflectance B26E Rrs(sr-1) Blue waters. Very low concentrations in SPM nm Beige waters: mineral suspended particles + Reflectance Rrs OPTIC-CONGO (805) Reflectance B Pic de fluorescence Rrs(sr-1) Rrs(sr-1) nm Dark brown waters: CDOM nm Green waters: phytoplancton + (Jourdin et al., 2006)

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8 Between 0 and 50 mg/l 1) Gironde plume. Relationship between suspended particulate matter concentrations and MODIS reflectances in bands 1 and 2 (250m resolution) SPMC(mg/L) = *Rrs(B1) 2) Adour plume SPMC(mg/L) = *Rrs(B1) (Petus et al., 2010)

9 3) French Guiana. ELISA-7 survey 2004, 4 7June Amazon turbid plume Modis/Aqua, 2004, June 5 SPMC(mg/L) = *Rrs(B1) (Froidefond et al., accepted)

10 SPM concentrations in the Bay of Arcachon from SPOT data Arcachon SPMC = *Rrs(B1) (Bru, 2010) Gabon and Congo coastal waters (Optic-Congo survey, SHOM, Schmeltz et al., 2009) No relationship

11 Summary of the measurements SPMC between 1 and 30 mg/l B1 (Modis Band nm 670nm) Gironde (turbid plume): Adour R. (Petus et al. 2010): French Guiana (turbid waters): Arcachon bay (Bru, 2010): Congo coast : Irish Sea (Binding et al., 2005): Mississipi plume (Miller et al): SPMC(mg/L) = *Rrs(B1) SPMC(mg/L) = *Rrs(B1) SPMC(mg/L) = *Rrs(B1) SPMC(mg/L) = *Rrs(B1) No relationship SPMC(mg/L) = 516.3*Rrs(665nm) SPMC(mg/L) = *Rrs(B1) 1.9 Different empirical relationships, explained by the optical properties of the water components: Various clay minerals (illite, kaolinite, chlorite, smectite ), quartz, micas Various granulometric size and flocs Concentration and composition of organic particles and CDOM. Comparison with a spectra simulation code (WASI)

12 WASI, Water color simulator (P. Gege, 2004) Initial values Fit parameters (output data) Chlorophyll concentration Fitted spectrum Original spectrum SPM concentration Exponent of yellow subst. absorption Yellow subst. (CDOM) concentration IOP (a, bb, Kd) P. Gege, 2004 Model and options: Rrs-(l) = frs*[bb(l) / (a(l) + bb(l))] and Rrs+(l) = xi*rrs-(l)/(1-sigma-*r)+rsurf with xi=1/nw2, sigma- = 0.54, nw = 0.33 frs = p1*(1+p2*x+p3*x2+p4*x3*[1+p5/cos(sun_w)]*[1+p7/cos(view_w)] (Albert and Mobley, 2003) Ancillary parameters: bottom depth, zenith angle

13 Example with MERIS data recorded during the Batel-1 survey MERIS June 5, 2007, 10h40 10h42 TU Station B5, June 5, 2007, 9h51 TU SPMC = 0.9mg/L, Chlor-a C. = 0.5mg/m3 Adour River (Schmeltz et al., 2010) Rrs reconstruction MERIS L2 and inversion from WASI Results with in situ SPMC and CDOM, but not with Chlorophyll a

14 Inversion of MERIS L2 spectrum (B5 station) from WASI Constituents and Z90 comparison for station B5 2 in_situ measurements 1.8 Concentrations from L2 products WASI derived values from in-situ spectrum 1.2 WASI derived values from MERIS L2 spectrum reconstructed Chlor (µg/l) SPM(mg/l) CDOM(1/m) Z90 max(m/10) at 530 nm BLACK: In-situ measurements GREEN: Concentration from MERIS-L2 products RED: WASI derived values from in-situ spectrum BLUE: WASI derived values from MERIS reconstructed spectrum Schmeltz et al., 2010

15 Conclusion 1) Improvement of the reflectance measurements with the radiance sensor juste below the water surface 2) Empirical algorithms are similar if the optical properties are similar, but the organic matter can change these relationships. The WASI code (P. Gege) allows to test different hypothesis and to inverse the reflectance spectra. Thank you