1. Tsapanou, A.1, Drakopoulos, P.2,Oikonomou, E.3 and Poulos, S.1
Estimating Suspended Particles Concentrations using Satellite and in-situ Ocean Color Measurements in the Region of Fresh Water Influence of River Evros - North Aegean Sea, Greece.
Tsapanou, A.1, Drakopoulos, P.2,Oikonomou, E.3 and Poulos, S.1
1Department of Geology & Geoenvironment, National & Kapodistrian University of Athens, Athens, Greece.
2Department of Optics and Optometry, Technological Educational Institute of Athens, Athens, Greece.
3Department of Civil Engineering and Surveying & Geoinformation, Technological Educational Institute of Athens, Athens, Greece.
objectives
methods
results
Estimation of suspended material concentrations from remote sensing data (Landsat-8) by using a single band algorithm.
Comparison of the results derived through ENVI & USGS analysis. Evaluation of the highest accuracy and reliability result.
Calibration of the estimated values by using in situ optical measurements and seasonal study of suspended material distribution through seawater circulation.
Development of optical methods for better correlation between the extracted turbidity from satellite images and the real concentrations of suspended material. First apply to Sentinel-2A imagery.
Cruise in NE Aegean on 2nd of June 2016 and sampling at 11 offshore positions:
Ocean Color Measurements
Above-surface radiance with a handheld portable spectroradiometer (JAZ Ocean Optics).
Hint: It calculates exactly what the satellite records, but more accurately, due to the bypass of atmospheric scattering.
Conversion of the in-situ remote sensing reflectance spectra to band values observed by the Landsat-8 & Sentinel-2A satellite sensors: the spectra are convolved with the sensors corresponding spectral responses, thus leading to a single value for each band.
SPM Field Data
Bottles of water sampling from the sea surface & the water column.
SPM (mg/l) derived through filtering (Pore diameter =0,45 μm).
Satellite Data
CORRELATION
USGS vs ENVI derived Estimations
Sentinel-2A
Lack of Sentinel imagery during our sampling
abstract
ENVI derived SPM
USGS derived SPM
This study investigates the potential of remotely sensed data to map surface suspended particulate matter (SPM) in the Continental shelf area of the North-East Aegean in Greece, by using Landsat-8 satellite sensor. Initially, simultaneous above water ocean color measurements were validated against SPM field data and compared to a concurrent Landsat-8 image, obtained on low river discharge period (June 2016). The satellite imagery was atmospherically corrected and Landsat-8 Surface Reflectance data were generated from:
the Landsat Surface Reflectance Code (LaSRC) provided by US Geological Survey and
the FLAASH algorithm within the ENVI software.
In both cases, the computed remote sensing reflectances (Rrs) from Landsat-8 are converted into SPM by adopting an algorithm based on single band analysis. After validation, the optical in-situ reflectances are correlated to Sentinel-2A corresponding spectral responses, thus leading to a single value for each band.
A comparison between Landsat-8 estimations of SPM and concurrent optical measurements at 11 stations indicates that satellite-derived concentrations tend to overestimate sea-truth. Image processing through ENVI & USGS shows 83% correlation, whereas the best linear correlation (90%) is observed between optical and USGS-derived values. The Sentinel-2A optical responses are quite similar to those of Landsat-8. We further discuss the improvements required in coupled studies of SPM retrieval within the coastal zone, the relationship between the examined remote sensors, as well as the necessity to evaluate the Sentinel-2A imagery performance, not only at surface but within the water column using in-situ measurements.
Correlation coefficient (r) 
SENTINEL2A JAZ
IN SITU
LANDSAT8 JAZ OPTICS
SENTINEL-2A
JAZ OPTICS 1
LANDSAT-8
Single Band algorithm (ρw)
ρw=Remote Sensing Reflectances (Rrs)
SPM= A × ρw /(1- ρw /C),
where for OLI Band 4 the tabulated values at 655nm are: A=289.2 gm-3 and C=
(Nechad et al, 2010)
Landsat-8
2/06/2016
ENVI PROCESSING-FLAASH TOOL
[Radiometric Calibration>Land & Cloud Masking>NaN Masking>Atmospheric Correction-ENVI FLAASH]
Rrs
USGS PROCESSING- (LaSRC Code)
SPM Retrieval
conclusions
Highest SPM values NW of Evros River Delta in dry season ( 4-6 mg/l).
Existence of plume at northern Samothraki island- under investigation.
Landsat-8 results overestimate the sea- truth derived from optical measurements.
ENVI image calibration in good correspondence with USGS image processing.
High correlation between optical and Landsat-8-USGS estimated Rrs & SPM values.
Sentinel-2A Optical responses very similar to Landsat-8 Optical responses for band 4.
Necessity to evaluate Sentinel-2A performance with concurrent in situ measurements & satellite passage.
results
Estimated SPM values on 2/6/2016 through all methods (mg/L) at [0-5m depth]
Statistical Analysis
background
Position
IN SITU
LANDSAT8
JAZ OPTICS
LANDSAT-USGS
LANDSAT-ENVI
SENTINEL2A JAZ s2
4,8200
1,1308
3,0494
2,2491
1,1180
a35
0,6000
0,2993
1,3419
1,4845
0,1696
a34a
2,1474
0,6846
1,3274
1,3671
0,4794
a34
0,1000
0,9324
2,1872
1,4661
0,7991
a32
5,5921
1,5941
3,0976
1,5707
1,4445
a24b
0,4000
1,0642
2,6538
1,8626
1,0457
a24
0,8600
0,4757
2,2745
1,1099
0,3224
a23
1,1800
0,8588
2,4204
1,2735
0,6154
a10
1,2000
0,1201
0,6236
0,7222
0,0742 a9
1,8600
0,1346
0,5519
0,6147
0,0736 a8
1,8000
0,2503
0,6042
0,6166
0,1586
Alexandroupolis Gulf - Evros River Delta:
Smooth slope, max depth=40m.
Evros river discharging: main influence (3,2 x 106 tones/year).
Suspended Particulate Matter:
Total suspended particles >2 microns found in the water column
Mean annual SPM in situ estimations: mg/l
Landsat-8 satellite data:
Ocean Color Optics:
The quantity that is monitored by satellites for SPM: Rrs
Defined as the ratio of the water-leaving spectral radiance to the downwelling spectral irradiance, both just above the water surface.
references
CORRELATION coefficient (r)
IN SITU
JAZ OPTICS
LANDSAT-USGS
LANDSAT-ENVI 1
Ruddick, K., B. Nechad, G. Neukermans, Y. Park, and D. Doxaran “Remote Sensing of Suspended Particulate Matter in Turbid Waters: State of the Art and Future Perspectives.” Proceedings of the Ocean Optics XIX Conference, Barga (Italy), October 6–10.
Dogliotti, A. I., K. G. Ruddick, B. Nechad, D. Doxaran, and E. Knaeps “A Single Algorithm to Retrieve Turbidity from Remotely-Sensed Data in All Coastal and Estuarine Waters.” Remote Sensing of Environment 156 (Jan.): 157–168. doi: /j.rse
Ouillion, S., Douillet, P., Andrefouet, S Coupling satellite data with in situ measurements and numerical modelling to study fine suspended-sediment transport: a study for the lagoon of New Caledonia, Coral Reefs 23:
Drakopoulos, P.G.1, Banks, A.C.2, 3, Kakagiannis, G.2, 4, Karageorgis, A.P.2, Lagaria, A.2, Papadopoulou, A.2, 4, Psarra, S.2, Spyridakis, N.2, Zervakis, V.4, Above and in-water remote sensing reflectance measurements during the AegeanMarTechproject: A first appraisal. 11th Panhellenic Symposium on Oceanography and Fisheries, Mytilene, Lesvos island, Greece.
Tsapanou, A., Oikonomou, E., Skianis, G. and Poulos, S., Estimation of surface suspended particulate matter concentration (SPM) in the outer Thermaikos Gulf, by using Landsat 8 data. 11th Panhellenic Symposium on Oceanography and Fisheries, Mytilene, Lesvos island, Greece, pp
Tsapanou, A., Tsepa, E., Poulos, S.E., Oikonomou, E., Sylaios, G. and Karditsa, A., Evaluation of multi-resolution satellite sensors for estimating surface suspended particulate matter concentration (SPM) in the gulf of Alexandroupolis, NE Aegean Sea, Greece. 3rd International Geocultural Symposium "Samaria", Chania, Crete, Greece., pp.34.
Vanhellemont, Q. and Ruddick, K Turbid wakes associated with offshore wind turbines observed with Landsat 8. Remote Sensing of Environment, 145, 105–115.
Instrument
SPM Band
Wavelength [nm]
Spatial Resolution [m]
Repeat cycle [days]
OLI
[11 bands] 4
650 30 16