SUSPENDED PARTICULATE MATTER ON A REGIONAL SCALE …earth.esa.int/workshops/meris_aatsr2005/... ·...
1
Fig.3. - Chlorophyll-“a” concentration [mg m -3 ] on the sea obtained from MERIS data (15.08.2002 09:59 UTC). SUSPENDED USPENDED USPENDED P P PARTICULATE ARTICULATE ARTICULATE M M MATTER ATTER ATTER (SPM) (SPM) (SPM) ON ON ON A R R REGIONAL EGIONAL EGIONAL S S SCALE CALE CALE (T (T (TUSCAN USCAN USCAN A A ARCHIPELAGO RCHIPELAGO RCHIPELAGO) ) ) FROM FROM FROM AVHRR AVHRR AVHRR AND AND AND MERIS D MERIS D MERIS DATA ATA ATA 10 9 8 7 6 5 4 3 2 1 0 Cinquale Nettuno Fiume Morto Foce Arno Livorno Antignano Rosignano L. M. di Castagneto Carbonifera Elba Nord Elba Mola Foce Ombrone Cala Forno Ansedonia Fig.2. Chlorophyll- “a” values meas- ured by ARPAT at 0.5 [m] depths on sites in Fig. 1 and values obtained from algorithms listed in Tab.1. o-o in situ Chl-”a” (22.08.2002) +-+ OC4v4, +-+ MERIS 2005, +-+ Santini, + + MUMM-CHL Chlorophyll-“a” [mg Tab.1a Correlation between in-situ Chlorophyll-“a” concentrations (all stations) and remote-sensed data, for the various analysed algorithms Chlorophyll-“a” Algorithms Correlation Mean Error RMS OC4v4 0.565 0.965 1.661 MERIS 2005 0.592 1.361 1.990 Santini 0.364 -0.836 1.804 MUMM-CHL -0.129 18.94 20.288 M. Tommasini, S. Mori, G. Poli, P. F. Pellegrini Unviversity of Florence - Electronics and Telecommunications Department Via di S. Marta, 3 — 50139 Firenze – Italy. e-mail: [email protected] ACKNOWLEDGMENTS The authors would like to thank ARPAT (Tuscan Regional Department for Environmental Protection) for their support in grounding in situ measure- ment obtained with oceanographic vessel “Poseidon” and to Dr. Michelle Johnson for her very useful collaboration in the organization of the paper and its text. Fig.4 - SPM concentration on the sea [mg/L] obtained from NOAA AVHRR data (15.08.2002 10:35 UTC) Fig.5. SST map [°C] from NOAA AVHRR data(15.08.2002 10:35 UTC). Fig.6. SPM concentration on the sea [mg/L] obtained from MERIS data (15.08.2002 09:59 UTC). ASTRACT Recent studies have shown the possibility to obtain concentrations of Suspended Particulate Matter (SPM) from satellite remote-sensed data, using images acquired by passive, multi-spectral sensors such as SeaWIFS, MERIS, and MODIS. Studies performed on the Belgian seafront indicated how it is possible to calibrate a NOAA-AVHRR algorithm for SPM calculations using measurements on chlorophyll-“a” ex- tracted from a local fixed station network. One limitation of this algorithm lies in the difficulty of obtain- ing chlorophyll-“a” values from larger areas of study. In our work we have explored the possibility of using MERIS chlorophyll-“a” maps to calibrate the SPM NOAA-AVHRR (SPM-AVHRR) algorithm along the Tuscan coast. This procedure has some advantages over the previous one: chlorophyll-“a” coverage of the entire SPM map, not just point-by-point coverage; the data fusion technique adopted permitted the increase of SPM informative contents taken from AVHRR data; the possibility to use near real time chlorophyll-“a” maps; the possibility to use directly ac- quired NOAA-AVHRR data. Our data are received by the Satellite Receiving Station of University Pole (PIN) of Prato – Italy (43°53',134 N; 11°05',942 E - WGS84). The MERIS algorithm used to calculate chlorophyll-“a” maps was chosen by comparing the results of 4 algorithms and in situ measurements. Sea truth data were taken from the ARPAT (Tuscan Regional De- partment for Environmental Protection) database. Presuming there is a limited variability of concentra- tion, a single MERIS chlorophyll-“a” map can be used to process more SPM-AVHRR maps. This chloro- phyll map will be periodically substituted with one that is closer to the last AVHRR image. The validity of this method was also verified through in-situ measurements, as well as SPM maps from MERIS images. The proposed method can be of great interest in continuous remote sensing observations of Turbidity and SPM by using near real time Full Resolution MERIS data. The best results can be acquired using MERIS data together with close-to-point ARPAT sea truth meau- rements. These data on the Tuscan Sea are at our disposal. Fig.1 - ARPAT Sea Measurement Sites and Stations, and mouths of the prin- cipal rivers. The material carried by the Tuscan Rivers Arno, Serchio and Ombrone, influences the sea areas opposite their mouths (red circle). Chlorophyll-“a”maps from MERIS data The SPM-AVHRR algorithm illustrated here uses MERIS chlorophyll-“a” maps (Fig.3). The chloro- phyll-“a” algorithm chosen is the MERIS-2005, the last version of the MERIS-ESA [3] (Eq.1), as it of- fers the best correlation (Tab.1a and Tab.1b) between in-situ measurement and analyzed algorithms: OC4v4 [11], MERIS 2005 [3], SANTINI [9] and MUMM-CHL [8]. The MERIS-2005 algorithm uses the maximum between the logarithmic reflectance ratios of MERIS bands 442, 490, 510 [nm], with respect to band 560 [nm] (r 442 , r 490 , r 510 and r 560 , [adim.] in Eq.1, while chlorophyll-“a” concentration is chl in [mg m -3 ]). Assuming that: and then: (1) The closest ARPAT measurements are 2 August and 22 August. From data analyses an average cor- relation emerged (Tab.1) between remote-sensed and in-situ measurements, with a tendency of over- estimating chlorophyll values. (Fig.2). The concentration map obtained is in Fig.3. { } 3 2 1 , , max r r r r = ( ) 4 3 2 2136 . 2 957 . 5 2272 . 5 4479 . 3 4245 . 0 log r r r r chl ⋅ + ⋅ − ⋅ + ⋅ − = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = 560 510 3 560 490 2 560 442 1 log , log , log ρ ρ ρ ρ ρ ρ r r r SUSPENDED PARTICULATE MATTER AND SEA TURBIDITY ISSUES Suspended Particulate Matter (SPM), Turbidity and Transparency are 3 physical and optical parameters that can be used for sea observation. A logical link between them can be defined. The Sea Turbidity parame- ter indicates a decrease in transparency due to the presence of sus- pended and/or dissolved substances. This depends on various ele- ments, such as rain, storms, soil and sea bottom erosion, flooding, aquatic flora and fauna, and salinity, but not by sea colour. For exam- ple, if there are many types of tannins present, the colouring is intense but is often very transparent. In turbid waters light is transmitted but also scattered, reflected, and reduced. Turbidity is defined as water’s capability of scattering light, measured in NTU (Nephelometric Turbid- ity Units), FTU (Formazin Turbidity Units), and JTU (Jackson Turbidity Units). The Transparency parameter evaluates the transparency of the water, which depends on light scattering and colouring as well. It is usually measured in Secchi Depth. Lastly, the suspended solids are the mass of the suspended material and can be measured in [mg/L] º [g m -3 ]. In literature it is often called Suspended Particulate Matter (SPM), or also Total Suspended Matter (TSM). Unlike the previous parameters, this one is a concentration and not an optic property. The SPM parameter is useful for monitoring the aquatic ecosystem, water drainage projects used as indicators of sedi- mentation movement, and in studies of land erosion. In compliance with regional, national, and European norms [10], AR- PAT has set up a monitoring network of the Tuscan coast. This net- work consists of 14 measuring sites with 3 stations per site at 500, 1000, and 3000 [m] from the coast, placed perpendicularly to it (transept) [1] (Fig.1). Measurements are taken at various depths from approximately 0.5 to 50 [m] for each station, and also include chloro- phyll-“a” [mg/m -3 ] and Turbidity [FTU]. Suspended solids [mg/L] are seasonally measured within 500[m] of the coast and 0.5 [m] in depth. SPM Maps from NOAA-AVHRR data The developed SPM-AVHRR algorithm uses AVHRR channel 1 (580 – 680 [nm]) data (Eq.2) and was developed based on the method described in [7]. The implemented model was refined integrating the solar radiance and the bio-optic sea model. The chlorophyll-“a” measurement used was incurred from MERIS data (see 2.5). The parameters described in Eq.2 are: L W (l) N [W cm -2 sr -1 mm -1 ] water leaving spectral radiance nor- malized for the incidence angle and atmospherically corrected; SPM [g m -3 ] SPM concentration; chl [mg m -3 ] for chlorophyll-“a”; b bw (l) = 1.103756E-3 [m -1 ] pure water backscattering spectral coefficient a w (l) = 0.297151 [m -1 ] and a w (440) = 0.00635000 [m -1 ] pure water absorption spectral coefficient; α(l) = 9.175e-3 [adim.] and β(l) = 0.099 [adim.] factors for determining the spectral coefficient of phyto- plankton specific absorption; k = 0.014 [nm -1 ] yellow substance spectral gradient; a s * = 0.003 [m 2 g -1 ] e b s * = 0.013 [m 2 g -1 ] SPM empirical parameters used in [7] for Belgian waters and tested here on Tuscan waters; m = 1.331678 [adim.] mean value of the pure water refraction index module; F 0 (J) = 0.162195 [W cm -2 ] average incident extraterrestrial spectral irradiance on the AVHRR channel 1 band corrected for the day of the year. Wavelengths are expressed in [nm]. Assuming that: then: (2) SPM-AVHRR algorithm limitations and assumptions made are: 1) the deal and constant in-band re- sponses by AVHRR channel 1 (580-680[nm]). The in-band mean value of solar irradiance, refraction index, pure seawater, phytoplankton, and yellow substance absorption and backscattering spectral coefficients were calculated with this hypothesis. The mean value of AVHRR channel 1 band (l = 630 [nm]) was used in calculating the yellow substance. 2) The model used for determining corrected so- lar radiance for the day of the year was greatly simplified. Nevertheless, the computed error can be disregarded, with respect to more sophisticated models. 3) The variation interval of the Sun’s zenith angle is considered 20-60 [deg]; the irradiance ratio R was calculated using a first order-simplified model, with a hypothesis of the diffusion over the entire hemisphere. The computed error is less than 20% [2]. 4) For the acquisition time difference, the MERIS chlorophyll and AVHRR SPM maps have different cloud situations. Given the near coincidental time and scarceness of clouds in the ex- ample considered, the same cloud mask was used for both chlorophyll-“a” and SPM. 5) Other limita- tions are due to the bio-optic models and the spectral tables used. Fig.4 shows the obtained SPM map. ( ) [ ] ( )( ) ( ) () [ ] ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ ⋅ + ⋅ − ⋅ − ⋅ = 2 0 2 48 . 0 0.043 1 0.021 1 1 m L J F m L R N w N w λ π λ ( ) ( ) [ ] ( ) ( ) ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + ⋅ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⋅ − ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − ⋅ + ⋅ ⋅ + ⋅ + + ⋅ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⋅ = − − + − * * * 65 . 0 440 1 0.0949 ] [ 06 . 0 440 2 . 0 ] [ 0.0949 S S S bw w k w bw b a R b b chl a e chl a b R SPM π α π λ β CONCLUSIONS The SPM-AVHRR algorithm described gave results that correspond with the measurements taken by ARPAT. The out-of-scale areas result as being around lakes, where suspended material values can actually be much higher, and in some small areas with probable cloud error detection (Fig.4 and Fig.6). On the contrary, the modified SPM-MERIS algorithm gave many false peaks on open waters, even if it gave trends similar to the AVHRR ones near the coast (Fig.7). Therefore further stud- ies are necessary on local calibration and validation of the SPM-MERIS algorithm. The illustrated SPM-AVHRR algorithm uses a chlorophyll-“a” concentration map obtained from MERIS data, with the MERIS-2005 algorithm described in 2.5. One advantage of this method is the possibilities to regionally and diffusely calibrate an entire SPM map with a chlorophyll-“a” one, unlike more traditional point-by- point methods. Moreover, using chlorophyll-“a” obtained from MERIS Full Resolution data, the resolution of the consequent SPM AVHRR maps intrinsically improves. Information about the sea given by the MERIS-AVHRR integrated system is completed by SST maps created from AVHRR data [1] (Fig.5). This method becomes particularly interesting if we think of the availability of MERIS and AVHRR data. MERIS data must be requested at ESA and there are poten- tially lengthy delivery dates, depending on the type of product requested (however, Near Real Time products are available a few hours after the passage). Moreover, there is a passage every three days on geographic area data. On the contrary, AVHRR data are very available and provide more passages per day. Future research should evaluate the relationship between the variation speed of chlorophyll-“a”, which is rather cyclic and barely influenced by intense events, with the variation of SPM concentration. The stability of the AVHRR SPM algorithm should also be evaluated with respect to the chlorophyll concentration map used. SPM [mg L -1 ] Cinquale Nettuno Fiume Morto Foce Arno Livorno Antignano Rosignano L. M. di Castagneto Carbonifera Elba Nord Elba Mola Foce Ombrone Cala Forno Ansedonia 30 27 24 21 18 15 12 9 6 3 0 Turbidity [FTU] 30 27 24 21 18 15 12 9 6 3 0 Fig.7—Turbidity and SPM values measured by ARPAT on sites in Fig.1 and values obtained from SPM-MERIS and SPM-AVHRR al- gorithms 0-0 In-situ Turbidity [FTU] (22.08.2002), + + in-situ SPM [mg/L] (02.09.2002), +-+ SPM AVHRR [mg/L], +-+ SPM MERIS [mg/L]
Transcript of SUSPENDED PARTICULATE MATTER ON A REGIONAL SCALE …earth.esa.int/workshops/meris_aatsr2005/... ·...
![Page 1: SUSPENDED PARTICULATE MATTER ON A REGIONAL SCALE …earth.esa.int/workshops/meris_aatsr2005/... · Fig.3. - Chlorophyll-“a” concentration [mg m-3] on the sea obtained from MERIS](https://reader035.fdocuments.net/reader035/viewer/2022081405/5f0cc6ec7e708231d4371445/html5/thumbnails/1.jpg)
Fig.3. - Chlorophyll-“a” concentration [mg m-3] on the sea obtained from MERIS data (15.08.2002 09:59 UTC).
SSSUSPENDEDUSPENDEDUSPENDED P P PARTICULATEARTICULATEARTICULATE M M MATTERATTERATTER (SPM) (SPM) (SPM) ONONON AAA R R REGIONALEGIONALEGIONAL S S SCALECALECALE (T (T (TUSCANUSCANUSCAN A A ARCHIPELAGORCHIPELAGORCHIPELAGO) ) )
FROMFROMFROM AVHRR AVHRR AVHRR ANDANDAND MERIS D MERIS D MERIS DATAATAATA
10
9
8
7
6
5
4
3
2
1
0
Cin
qual
e N
ettu
no
Fium
e M
orto
Fo
ce A
rno
Livo
rno
Ant
igna
no
Ros
igna
no L
. M
. di C
asta
gnet
o C
arbo
nife
ra
Elb
a N
ord
Elb
a M
ola
Foce
Om
bron
e C
ala
Forn
o A
nsed
onia
Fig.2. Chlorophyll-“a” values meas-ured by ARPAT at 0.5 [m] depths on sites in Fig. 1 and values obtained from algorithms listed in Tab.1. o-o in situ Chl-”a” (22.08.2002) +-+ OC4v4, +-+ MERIS 2005, +-+ Santini, + + MUMM-CHL
Chl
orop
hyll-
“a” [
mg
Tab.1a Correlation between in-situ Chlorophyll-“a” concentrations (all stations) and remote-sensed data, for the various analysed algorithms
Chlorophyll-“a” Algorithms
Correlation Mean Error RMS
OC4v4 0.565 0.965 1.661 MERIS 2005 0.592 1.361 1.990 Santini 0.364 -0.836 1.804 MUMM-CHL -0.129 18.94 20.288
M. Tommasini, S. Mori, G. Poli, P. F. Pellegrini
Unviversity of Florence - Electronics and
Telecommunications Department Via di S. Marta, 3 — 50139 Firenze – Italy.
e-mail: [email protected] ACKNOWLEDGMENTS The authors would like to thank ARPAT (Tuscan Regional Department for Environmental Protection) for their support in grounding in situ measure-ment obtained with oceanographic vessel “Poseidon” and to Dr. Michelle Johnson for her very useful collaboration in the organization of the paper and its text.
Fig.4 - SPM concentration on the sea [mg/L] obtained from NOAA AVHRR data (15.08.2002 10:35 UTC)
Fig.5. SST map [°C] from NOAA AVHRR data(15.08.2002 10:35 UTC).
Fig.6. SPM concentration on the sea [mg/L] obtained from MERIS data (15.08.2002 09:59 UTC).
ASTRACT Recent studies have shown the possibility to obtain concentrations of Suspended Particulate Matter (SPM) from satellite remote-sensed data, using images acquired by passive, multi-spectral sensors such as SeaWIFS, MERIS, and MODIS. Studies performed on the Belgian seafront indicated how it is possible to calibrate a NOAA-AVHRR algorithm for SPM calculations using measurements on chlorophyll-“a” ex-tracted from a local fixed station network. One limitation of this algorithm lies in the difficulty of obtain-ing chlorophyll-“a” values from larger areas of study. In our work we have explored the possibility of using MERIS chlorophyll-“a” maps to calibrate the SPM NOAA-AVHRR (SPM-AVHRR) algorithm along the Tuscan coast. This procedure has some advantages over the previous one: chlorophyll-“a” coverage of the entire SPM map, not just point-by-point coverage; the data fusion technique adopted permitted the increase of SPM informative contents taken from AVHRR data; the possibility to use near real time chlorophyll-“a” maps; the possibility to use directly ac-quired NOAA-AVHRR data. Our data are received by the Satellite Receiving Station of University Pole (PIN) of Prato – Italy (43°53',134 N; 11°05',942 E - WGS84). The MERIS algorithm used to calculate chlorophyll-“a” maps was chosen by comparing the results of 4 algorithms and in situ measurements. Sea truth data were taken from the ARPAT (Tuscan Regional De-partment for Environmental Protection) database. Presuming there is a limited variability of concentra-tion, a single MERIS chlorophyll-“a” map can be used to process more SPM-AVHRR maps. This chloro-phyll map will be periodically substituted with one that is closer to the last AVHRR image. The validity of this method was also verified through in-situ measurements, as well as SPM maps from MERIS images. The proposed method can be of great interest in continuous remote sensing observations of Turbidity and SPM by using near real time Full Resolution MERIS data. The best results can be acquired using MERIS data together with close-to-point ARPAT sea truth meau-rements. These data on the Tuscan Sea are at our disposal.
Fig.1 - ARPAT Sea Measurement Sites and Stations, and mouths of the prin-cipal rivers. The material carried by the Tuscan Rivers Arno, Serchio and Ombrone, influences the sea areas opposite their mouths (red circle).
Chlorophyll-“a”maps from MERIS data The SPM-AVHRR algorithm illustrated here uses MERIS chlorophyll-“a” maps (Fig.3). The chloro-phyll-“a” algorithm chosen is the MERIS-2005, the last version of the MERIS-ESA [3] (Eq.1), as it of-fers the best correlation (Tab.1a and Tab.1b) between in-situ measurement and analyzed algorithms: OC4v4 [11], MERIS 2005 [3], SANTINI [9] and MUMM-CHL [8]. The MERIS-2005 algorithm uses the maximum between the logarithmic reflectance ratios of MERIS bands 442, 490, 510 [nm], with respect to band 560 [nm] (r442, r490, r510 and r560, [adim.] in Eq.1, while chlorophyll-“a” concentration is chl in [mg m-3]). Assuming that: and then: (1) The closest ARPAT measurements are 2 August and 22 August. From data analyses an average cor-relation emerged (Tab.1) between remote-sensed and in-situ measurements, with a tendency of over-estimating chlorophyll values. (Fig.2). The concentration map obtained is in Fig.3.
{ }321 ,,max rrrr =
( ) 432 2136.2957.52272.54479.34245.0log rrrrchl ⋅+⋅−⋅+⋅−=
⎟⎟⎠
⎞⎜⎜⎝
⎛=⎟⎟
⎠
⎞⎜⎜⎝
⎛=⎟⎟
⎠
⎞⎜⎜⎝
⎛=
560
5103
560
4902
560
4421 log,log,log
ρρ
ρρ
ρρ rrr
SUSPENDED PARTICULATE MATTER AND SEA TURBIDITY ISSUES
Suspended Particulate Matter (SPM), Turbidity and Transparency are 3
physical and optical parameters that can be used for sea observation.
A logical link between them can be defined. The Sea Turbidity parame-
ter indicates a decrease in transparency due to the presence of sus-
pended and/or dissolved substances. This depends on various ele-
ments, such as rain, storms, soil and sea bottom erosion, flooding,
aquatic flora and fauna, and salinity, but not by sea colour. For exam-
ple, if there are many types of tannins present, the colouring is intense
but is often very transparent. In turbid waters light is transmitted but
also scattered, reflected, and reduced. Turbidity is defined as water’s
capability of scattering light, measured in NTU (Nephelometric Turbid-
ity Units), FTU (Formazin Turbidity Units), and JTU (Jackson Turbidity
Units).
The Transparency parameter evaluates the transparency of the water,
which depends on light scattering and colouring as well. It is usually
measured in Secchi Depth.
Lastly, the suspended solids are the mass of the suspended material
and can be measured in [mg/L] º [g m-3]. In literature it is often called
Suspended Particulate Matter (SPM), or also Total Suspended Matter
(TSM). Unlike the previous parameters, this one is a concentration and
not an optic property. The SPM parameter is useful for monitoring the
aquatic ecosystem, water drainage projects used as indicators of sedi-
mentation movement, and in studies of land erosion.
In compliance with regional, national, and European norms [10], AR-
PAT has set up a monitoring network of the Tuscan coast. This net-
work consists of 14 measuring sites with 3 stations per site at 500,
1000, and 3000 [m] from the coast, placed perpendicularly to it
(transept) [1] (Fig.1). Measurements are taken at various depths from
approximately 0.5 to 50 [m] for each station, and also include chloro-
phyll-“a” [mg/m-3] and Turbidity [FTU]. Suspended solids [mg/L] are
seasonally measured within 500[m] of the coast and 0.5 [m] in depth.
SPM Maps from NOAA-AVHRR data The developed SPM-AVHRR algorithm uses AVHRR channel 1 (580 – 680 [nm]) data (Eq.2) and was developed based on the method described in [7]. The implemented model was refined integrating the solar radiance and the bio-optic sea model. The chlorophyll-“a” measurement used was incurred from MERIS data (see 2.5). The parameters described in Eq.2 are: LW(l)N [W cm-2 sr-1 mm-1] water leaving spectral radiance nor-malized for the incidence angle and atmospherically corrected; SPM [g m-3] SPM concentration; chl [mg m-3] for chlorophyll-“a”; bbw(l) = 1.103756E-3 [m-1] pure water backscattering spectral coefficient aw(l) = 0.297151 [m-1] and aw(440) = 0.00635000 [m-1] pure water absorption spectral coefficient; α(l) = 9.175e-3 [adim.] and β(l) = 0.099 [adim.] factors for determining the spectral coefficient of phyto-plankton specific absorption; k = 0.014 [nm-1] yellow substance spectral gradient; as* = 0.003 [m2 g-1] e bs* = 0.013 [m2 g-1] SPM empirical parameters used in [7] for Belgian waters and tested here on Tuscan waters; m = 1.331678 [adim.] mean value of the pure water refraction index module; F0(J) = 0.162195 [W cm-2] average incident extraterrestrial spectral irradiance on the AVHRR channel 1 band corrected for the day of the year. Wavelengths are expressed in [nm]. Assuming that: then:
(2) SPM-AVHRR algorithm limitations and assumptions made are: 1) the deal and constant in-band re-sponses by AVHRR channel 1 (580-680[nm]). The in-band mean value of solar irradiance, refraction index, pure seawater, phytoplankton, and yellow substance absorption and backscattering spectral coefficients were calculated with this hypothesis. The mean value of AVHRR channel 1 band (l = 630 [nm]) was used in calculating the yellow substance. 2) The model used for determining corrected so-lar radiance for the day of the year was greatly simplified. Nevertheless, the computed error can be disregarded, with respect to more sophisticated models. 3) The variation interval of the Sun’s zenith angle is considered 20-60 [deg]; the irradiance ratio R was calculated using a first order-simplified model, with a hypothesis of the diffusion over the entire hemisphere. The computed error is less than 20% [2]. 4) For the acquisition time difference, the MERIS chlorophyll and AVHRR SPM maps have different cloud situations. Given the near coincidental time and scarceness of clouds in the ex-ample considered, the same cloud mask was used for both chlorophyll-“a” and SPM. 5) Other limita-tions are due to the bio-optic models and the spectral tables used. Fig.4 shows the obtained SPM map.
( )[ ]( ) ( ) ( ) ( )[ ] ⎥⎦
⎤⎢⎣⎡ ⋅⋅+⋅−⋅−
⋅=
20
2
48.00.04310.02111 mLJF
mLR
Nw
Nw
λπ
λ
( ) ( )[ ]( )
( )⎥⎦
⎤⎢⎣
⎡+⋅⎟
⎠⎞
⎜⎝⎛
⋅−
⎥⎦
⎤⎢⎣
⎡−⋅+⋅⋅+⋅++⋅⎟
⎠⎞
⎜⎝⎛
⋅=
−−+−
***
65.04401
0.0949
][06.04402.0][0.0949
SSS
bwwk
wbw
baRb
bchlaechlabR
SPM
π
απ
λβ
CONCLUSIONS The SPM-AVHRR algorithm described gave results that correspond with the measurements taken by ARPAT. The out-of-scale areas result as being around lakes, where suspended material values can actually be much higher, and in some small areas with probable cloud error detection (Fig.4 and Fig.6). On the contrary, the modified SPM-MERIS algorithm gave many false peaks on open waters, even if it gave trends similar to the AVHRR ones near the coast (Fig.7). Therefore further stud-ies are necessary on local calibration and validation of the SPM-MERIS algorithm. The illustrated SPM-AVHRR algorithm uses a chlorophyll-“a” concentration map obtained from MERIS data, with the MERIS-2005 algorithm described in 2.5. One advantage of this method is the possibilities to regionally and diffusely calibrate an entire SPM map with a chlorophyll-“a” one, unlike more traditional point-by-point methods. Moreover, using chlorophyll-“a” obtained from MERIS Full Resolution data, the resolution of the consequent SPM AVHRR maps intrinsically improves. Information about the sea given by the MERIS-AVHRR integrated system is completed by SST maps created from AVHRR data [1] (Fig.5). This method becomes particularly interesting if we think of the availability of MERIS and AVHRR data. MERIS data must be requested at ESA and there are poten-tially lengthy delivery dates, depending on the type of product requested (however, Near Real Time products are available a few hours after the passage). Moreover, there is a passage every three days on geographic area data. On the contrary, AVHRR data are very available and provide more passages per day. Future research should evaluate the relationship between the variation speed of chlorophyll-“a”, which is rather cyclic and barely influenced by intense events, with the variation of SPM concentration. The stability of the AVHRR SPM algorithm should also be evaluated with respect to the chlorophyll concentration map used.
SP
M [m
g L-1
]
Cin
qual
e N
ettu
no
Fium
e M
orto
Fo
ce A
rno
Livo
rno
Ant
igna
no
Ros
igna
no L
. M
. di C
asta
gnet
o C
arbo
nife
ra
Elb
a N
ord
Elba
Mol
a Fo
ce O
mbr
one
Cal
a Fo
rno
Ans
edon
ia
30
27
24
21
18
15
12
9
6
3
0
Turb
idity
[FTU
]
30
27
24
21
18
15
12
9
6
3
0
Fig.7—Turbidity and SPM values measured by ARPAT on sites in Fig.1 and values obtained from SPM-MERIS and SPM-AVHRR al-gorithms 0-0 In-situ Turbidity [FTU] (22.08.2002), + + in-situ SPM [mg/L] (02.09.2002), +-+ SPM AVHRR [mg/L], +-+ SPM MERIS [mg/L]
