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Fig. 1. Study area and location of fieldwork activities performed within a 3-hour interval around the image acquisition. | to 9 are the stations where water was sampled for laboratory analysis for chlorophyll-a and tripton concentrations (stations 4, 6 and 7 have also PR-650 radiometric measurements). The flow- through system was cruised throughout all the stations, for a length of about 32 km. The 7.5-km-wide portion of lake imaged by Hyperion is outlined.

Figure 1 Study area and location of fieldwork activities performed within a 3-hour interval around the image acquisition. | to 9 are the stations where water was sampled for laboratory analysis for chlorophyll-a and tripton concentrations (stations 4, 6 and 7 have also PR-650 radiometric measurements). The flow- through system was cruised throughout all the stations, for a length of about 32 km. The 7.5-km-wide portion of lake imaged by Hyperion is outlined.

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This article was originally published in a journal published by Elsevier, and the attached copy is provided by Elsevier for the author’s benefit and for the benefit of the author’s institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues that you know, and providing a copy to your institution’s administrator.
This article was originally published in a journal published by Elsevier, and the attached copy is provided by Elsevier for the author’s benefit and for the benefit of the author’s institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues that you know, and providing a copy to your institution’s administrator.
Fig. 2. Scatter plots of fluorescence vs. chlorophyll-a (using stations | to 8) and of turbidity vs. tripton (using stations 2 to 9) with the calibration lines (turbidity in Station | and fluorescence in Station 9 were no available). at 750 nm (Toole et al., 2000). Literature data (Toole et al., 2000) for clear sky and high wind speeds were used (on 22nd July, 2003 the average wind speed on the lake was 6 ms _'). Assuming an air/water interface parameter of 0.533 (Lee et al., 1994) and a Q-factor of 4.2 sr ' the roughness-cor- rected Rrs(0+, 4) were then transformed into R(0-, A) values. As reported in Strémbeck et al. (2003) the Q-factor was the average, between 400 and 750 nm, of a spectral Q- factor computed using the HYDROLIGHT 4.2 model (Mobley, 1994; Mobley & Sundman, 2001). tion spectra of coloured dissolved organic matter. In this study Scpom and Srp were equal to 0.021 and 0.012, respectively.
Fig. 2. Scatter plots of fluorescence vs. chlorophyll-a (using stations | to 8) and of turbidity vs. tripton (using stations 2 to 9) with the calibration lines (turbidity in Station | and fluorescence in Station 9 were no available). at 750 nm (Toole et al., 2000). Literature data (Toole et al., 2000) for clear sky and high wind speeds were used (on 22nd July, 2003 the average wind speed on the lake was 6 ms _'). Assuming an air/water interface parameter of 0.533 (Lee et al., 1994) and a Q-factor of 4.2 sr ' the roughness-cor- rected Rrs(0+, 4) were then transformed into R(0-, A) values. As reported in Strémbeck et al. (2003) the Q-factor was the average, between 400 and 750 nm, of a spectral Q- factor computed using the HYDROLIGHT 4.2 model (Mobley, 1994; Mobley & Sundman, 2001). tion spectra of coloured dissolved organic matter. In this study Scpom and Srp were equal to 0.021 and 0.012, respectively.
List of the bio-optical parameters and in situ water quality data presented in this study with information about the day of acquisition and data source (APPA is the Environmental Protection Agency of Trento, ARPAV is the Environmental Protection Agency of Veneto) October 2002, they were averaged and integrated in the existing dataset. Apparently, the natural modifications of algal and tripton compositions occurred between the two periods had a negligible effect on their absorption spectral properties. Together with the M4(A)/H,(A) ratio (average value from 450 nm to 750 nm equal to 0.327), that was derived running HYDROLIGHT 4.2 with inputs typical of Lake Garda (e.g., IOPs, averages values of wind speed and visibility ranges, summertime Sun zenith angles at 11+1 h UTC) (Strémbeck et al., 2003), these SIOPs uniquely characterise the parameter- isation of Eq. (1) for Lake Garda waters. Table 1 summarises the bio-optical model parameters with the day of acquisition and the data provider, Fig. 3 shows the SIOPs used in this study.
List of the bio-optical parameters and in situ water quality data presented in this study with information about the day of acquisition and data source (APPA is the Environmental Protection Agency of Trento, ARPAV is the Environmental Protection Agency of Veneto) October 2002, they were averaged and integrated in the existing dataset. Apparently, the natural modifications of algal and tripton compositions occurred between the two periods had a negligible effect on their absorption spectral properties. Together with the M4(A)/H,(A) ratio (average value from 450 nm to 750 nm equal to 0.327), that was derived running HYDROLIGHT 4.2 with inputs typical of Lake Garda (e.g., IOPs, averages values of wind speed and visibility ranges, summertime Sun zenith angles at 11+1 h UTC) (Strémbeck et al., 2003), these SIOPs uniquely characterise the parameter- isation of Eq. (1) for Lake Garda waters. Table 1 summarises the bio-optical model parameters with the day of acquisition and the data provider, Fig. 3 shows the SIOPs used in this study.
On 22nd June 2003, image data from an area of 7.5 by 42 km was acquired by Hyperion with a near-nadir viewing. At the time of the overpass Sun zenith and azimuth angles were 32° and 136°, respectively. For this study 28 Hyperion spectral bands ranging from 480 nm to 750 nm were selected to be relevant for WQPs estimation and reliable for the sensor calibration (Green et al., 2003). Following the approach by Brando and Dekker (2003), the image was convolved using a
On 22nd June 2003, image data from an area of 7.5 by 42 km was acquired by Hyperion with a near-nadir viewing. At the time of the overpass Sun zenith and azimuth angles were 32° and 136°, respectively. For this study 28 Hyperion spectral bands ranging from 480 nm to 750 nm were selected to be relevant for WQPs estimation and reliable for the sensor calibration (Green et al., 2003). Following the approach by Brando and Dekker (2003), the image was convolved using a
values RMSE and relative RMSE for each station are reported together with their average value (in bold); Avo is the average for stations 4, 6 and 7 of RMSEs computed from in situ and forward-modelled R(O—, 2) values, Avpyp is the average for stations 4, 6 and 7 of RMSEs computed from in situ and Hyperion-derived R(O-, 2) values. Avay is the average of AVioaq and Avyyp RMSEs and measures how R(0-, 2) values from Hyperion, forward bio-optical modelling and in situ optical data converge. RMSEs and relative RMSEs are separately computed for VIS (22 bands from 480 to 690 nm) and NIR (6 bands from 700 to 750 nm) ranges.
values RMSE and relative RMSE for each station are reported together with their average value (in bold); Avo is the average for stations 4, 6 and 7 of RMSEs computed from in situ and forward-modelled R(O—, 2) values, Avpyp is the average for stations 4, 6 and 7 of RMSEs computed from in situ and Hyperion-derived R(O-, 2) values. Avay is the average of AVioaq and Avyyp RMSEs and measures how R(0-, 2) values from Hyperion, forward bio-optical modelling and in situ optical data converge. RMSEs and relative RMSEs are separately computed for VIS (22 bands from 480 to 690 nm) and NIR (6 bands from 700 to 750 nm) ranges.
Fig. 4. In situ, forward-modelled and Hyperion-derived subsurface irradiance reflectance R(O-, 2) spectra in stations 4, 6 and 7 (Fig. 1): “In situ” spectra are derived from above-water measurements of Rrs(0+, 2); “Model” spectra are calculated from forward bio-optical modelling using CHL-a (in mgm *) and TR (in gm *) concentrations measured in situ (shown in each graph) and assuming acpom(440)=0.09 m~' in all stations; “Hyp” spectra are computed from Hyperion imagery using the c- WOMBAT-c atmospheric correction code. All the data were collected on 22nd July 2003. Average reflectance RMSEs (see also Table 2) are 0.006 (relative RMSE 13%) between 480 and 690 nm, and 0.011 (relative RMSE 66%) beyond 700 nm.
Fig. 4. In situ, forward-modelled and Hyperion-derived subsurface irradiance reflectance R(O-, 2) spectra in stations 4, 6 and 7 (Fig. 1): “In situ” spectra are derived from above-water measurements of Rrs(0+, 2); “Model” spectra are calculated from forward bio-optical modelling using CHL-a (in mgm *) and TR (in gm *) concentrations measured in situ (shown in each graph) and assuming acpom(440)=0.09 m~' in all stations; “Hyp” spectra are computed from Hyperion imagery using the c- WOMBAT-c atmospheric correction code. All the data were collected on 22nd July 2003. Average reflectance RMSEs (see also Table 2) are 0.006 (relative RMSE 13%) between 480 and 690 nm, and 0.011 (relative RMSE 66%) beyond 700 nm.
Fig. 5. Sensitivity analysis for the band selection of the MIM image inversion. (a): first derivative spectra of R(0-, A) vs. dcpom(440), rescaled by a 0.01 factor (acpom(440) concentration was changed from 0.03 to 0.30 m— ' the other two WQPs were kept constant to CHL-a=1 mg m ? and TR=1 g m °); (b): first derivative spectra of R(O-, A) vs. CHL-a (CHL-a concentration was changed from 1 to 10 mg m °, the other two WQPs were kept constant to acpom(440) =0.09 m | and TR=1 gm °); (c): first derivate spectra of R(0-, A) vs. TR (TR concentration was changed from 1 to 10 g m °, the other two WQPs were kept constant to dcpom(440)=0.09 m | and CHL-a=1 mg m °). The NEAR(0-, A)z of Hyperion is overlaid on each of the graphs as dot lines. The box indicates the wavelength range of Hyperion bands that may be used. Note the different y axis ranges of each plot. The first derivative spectra relative to variations of acpom (440) were obtained from 10 forward runs of the bio-optical
Fig. 5. Sensitivity analysis for the band selection of the MIM image inversion. (a): first derivative spectra of R(0-, A) vs. dcpom(440), rescaled by a 0.01 factor (acpom(440) concentration was changed from 0.03 to 0.30 m— ' the other two WQPs were kept constant to CHL-a=1 mg m ? and TR=1 g m °); (b): first derivative spectra of R(O-, A) vs. CHL-a (CHL-a concentration was changed from 1 to 10 mg m °, the other two WQPs were kept constant to acpom(440) =0.09 m | and TR=1 gm °); (c): first derivate spectra of R(0-, A) vs. TR (TR concentration was changed from 1 to 10 g m °, the other two WQPs were kept constant to dcpom(440)=0.09 m | and CHL-a=1 mg m °). The NEAR(0-, A)z of Hyperion is overlaid on each of the graphs as dot lines. The box indicates the wavelength range of Hyperion bands that may be used. Note the different y axis ranges of each plot. The first derivative spectra relative to variations of acpom (440) were obtained from 10 forward runs of the bio-optical
Validation OF ChiL-a and Ik HMyperion-derived Maps was performed using in situ point stations. Fig. 7 shows the two scatter plots depicting the Hyperion-derived CHL-a and TR estimations vs. in situ concentrations measured in 8 pelagic stations (all the stations in Fig. 1, except Station 1 which is located in shallow waters where Hyperion data were masked to avoid bathymetric effects). Hyperion data was averaged on a 3 by 3 pixel region of interest centred on the location of in situ sampling stations. The Hyperion-derived CHL-a was in good agreement with in situ point data, showing a correlation coefficient (r) of 0.77, a determination coefficient (R) of 0.59, a RMSE of 0.36 mg m ° (relative RMSE 20%), a bias of 0.12 mg m ° (relative bias 6%), and being close to the 1:1 line (Fig. 7). The RMSE and the relative RMSE were computed with Eqs. (5) and (6), where N is now equal to 8 (i.e., the number of stations), and Y; and X; are the in situ observed and the Fig. 6 presents the pseudo true colour Hyperion image and the two WQP maps retrieved applying the MIM to the image. The pseudo true colour Hyperion image qualitatively describes the diversity of waters within the lake. The turquoise—cyan colours in the southern part of the lake are due to bottom effects of bright substrates. Most of the deep waters are dark-blue but lighter blue waters come up about the middle of the scene, as well as in the south, on the western side of the peninsula. On 22nd July 2003, re-suspension of sediments was caused by the strong wind action resulting in variable patterns of more highly Fig. 6. The pseudo true colour Hyperion image (with locations of point in situ stations) and the two MIM-retrieved products obtained from Hyperion data acquired o 22nd July 2003. In the product maps shallow waters are masked.
Validation OF ChiL-a and Ik HMyperion-derived Maps was performed using in situ point stations. Fig. 7 shows the two scatter plots depicting the Hyperion-derived CHL-a and TR estimations vs. in situ concentrations measured in 8 pelagic stations (all the stations in Fig. 1, except Station 1 which is located in shallow waters where Hyperion data were masked to avoid bathymetric effects). Hyperion data was averaged on a 3 by 3 pixel region of interest centred on the location of in situ sampling stations. The Hyperion-derived CHL-a was in good agreement with in situ point data, showing a correlation coefficient (r) of 0.77, a determination coefficient (R) of 0.59, a RMSE of 0.36 mg m ° (relative RMSE 20%), a bias of 0.12 mg m ° (relative bias 6%), and being close to the 1:1 line (Fig. 7). The RMSE and the relative RMSE were computed with Eqs. (5) and (6), where N is now equal to 8 (i.e., the number of stations), and Y; and X; are the in situ observed and the Fig. 6 presents the pseudo true colour Hyperion image and the two WQP maps retrieved applying the MIM to the image. The pseudo true colour Hyperion image qualitatively describes the diversity of waters within the lake. The turquoise—cyan colours in the southern part of the lake are due to bottom effects of bright substrates. Most of the deep waters are dark-blue but lighter blue waters come up about the middle of the scene, as well as in the south, on the western side of the peninsula. On 22nd July 2003, re-suspension of sediments was caused by the strong wind action resulting in variable patterns of more highly Fig. 6. The pseudo true colour Hyperion image (with locations of point in situ stations) and the two MIM-retrieved products obtained from Hyperion data acquired o 22nd July 2003. In the product maps shallow waters are masked.
Fig. 7. Scatter plots of Hyperion-derived products and in situ concentrations measured in point stations: on left for chlorophyll-a, on right for tripton. Dot lines indicate the 1:1 relation. Both graphs do not include data from Stations | because it is located in the shallow waters. The statistic in the tripton graph does not include the black symbol (i.e., Station 5).
Fig. 7. Scatter plots of Hyperion-derived products and in situ concentrations measured in point stations: on left for chlorophyll-a, on right for tripton. Dot lines indicate the 1:1 relation. Both graphs do not include data from Stations | because it is located in the shallow waters. The statistic in the tripton graph does not include the black symbol (i.e., Station 5).
Fig. 8. Comparison of Hyperion-derived products and in situ concentrations estimated from the flow-through data along the horizontal transect: (a) chlorophyll-a, (b tripton. Hyperion and flow-through transect data are extracted from a 30 m per 30 m pixel grid (see text for labels I to 1V). The approximate location of transect in siti data with respect to the time of Hyperion overpass is also indicated.
Fig. 8. Comparison of Hyperion-derived products and in situ concentrations estimated from the flow-through data along the horizontal transect: (a) chlorophyll-a, (b tripton. Hyperion and flow-through transect data are extracted from a 30 m per 30 m pixel grid (see text for labels I to 1V). The approximate location of transect in siti data with respect to the time of Hyperion overpass is also indicated.
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TechnologyRemote SensingGeomatic EngineeringAtmospheric CorrectionLight fieldWater quality monitoringNoise MeasurementInherent Optical PropertiesColoured Dissolved Organic Matter
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