because of the multiple uses of its waters. Similar to other subalpine lakes
(e.g. Maggiore, Como, Iseo and Idro), it represents an essential strategic water
supply for agriculture, industry, fishing and drinking. In its southern part, Lake
Garda is characterised by gentle slopes which facilitate the growth of submerged
macrophytes and the emergent Phragmites australis in the coastal zone. This
ecosystem is highly vulnerable to anthropogenic perturbations (e.g. water level
variations for agriculture and energy use and navigation), and according to the
European rules [84] rigorous monitoring of the lake is required. In this context, high
spatial and high spectral resolutions provide opportunities for cost-effective qualitative and quantitative analyses of the macrophyte distribution and change.
MIVIS imagery was acquired on 16 September 1997, 27 July 2005, 15 July 2010
and 27 June 2011 for the southern part of Lake Garda (Sirmione Peninsula). During
the airborne campaign performed on 27 June 2011, a flight plan consisting of
12 runs was successfully accomplished covering the entire coastline of Lake
Garda. The airborne campaigns were always performed synchronously with fieldwork activities aiming to gather data for the calibration of a bio-optical model and
assessing the MIVIS-derived products.
MIVIS data were corrected for atmospheric effects with either 6S or ATCOR-4,
the latter used in the latest acquisitions. The classification of submerged macrophytes and uncolonised sandy substrates was achieved by the spectral inversion of
the atmospherically corrected MIVIS reflectances. Similarly to Lake Trasimeno,
the spectral inversion was achieved with BOMBER where the implemented
bio-optical model for shallow waters was parameterised with data gathered from
fieldwork activities—in excess of 60 days over 10 years of in situ measurements.
The bottom cover identification has been mapped considering bottom depths
(i.e. those estimated with BOMBER synchronously with retrieval of bottom
types) lower than 7 m, according to Giardino et al. [69], which is the limit of
sensitivity of the model in Lake Garda waters.
Figure 6 shows the distribution of macrophytes in the whole Lake Garda: in the
northern and in the central parts, the presence of macrophytes is small because the
morphological characteristics (slopes descending fast to the lake) are not suitable
for the growth of macrophytes; conversely depth gradients in the southern Lake
Garda facilitate the growth of macrophytes. About 20.5 km
2 of shallow waters
(i.e. bottom depth <7 m) has been mapped: approximately 17 km
2 is characterised
by the presence of macrophytes, even if in some cases sparse.
Figure 7 shows the histogram depicting the height of the water column above the
canopy in the Sirmione Peninsula area (cf. Fig. 6, zoom with the red frame) as
derived by the MIVIS data collected from 1997 to 2011, according to the procedure
described above (for more details refer to Bresciani et al. [67] and Giardino
et al. [69]). The height of the water column above macrophytes is plotted together
with water level fluctuation and water clarity (both derived from in situ measurements); the macrophyte distribution along the littoral zone of the Sirmione Peninsula might be linked to those two physical parameters; thus, the macrophyte change
is then a consequence of both the anthropogenic pressure and meteo-climatic
variations.
72
C. Giardino et al.
(e.g. Maggiore, Como, Iseo and Idro), it represents an essential strategic water
supply for agriculture, industry, fishing and drinking. In its southern part, Lake
Garda is characterised by gentle slopes which facilitate the growth of submerged
macrophytes and the emergent Phragmites australis in the coastal zone. This
ecosystem is highly vulnerable to anthropogenic perturbations (e.g. water level
variations for agriculture and energy use and navigation), and according to the
European rules [84] rigorous monitoring of the lake is required. In this context, high
spatial and high spectral resolutions provide opportunities for cost-effective qualitative and quantitative analyses of the macrophyte distribution and change.
MIVIS imagery was acquired on 16 September 1997, 27 July 2005, 15 July 2010
and 27 June 2011 for the southern part of Lake Garda (Sirmione Peninsula). During
the airborne campaign performed on 27 June 2011, a flight plan consisting of
12 runs was successfully accomplished covering the entire coastline of Lake
Garda. The airborne campaigns were always performed synchronously with fieldwork activities aiming to gather data for the calibration of a bio-optical model and
assessing the MIVIS-derived products.
MIVIS data were corrected for atmospheric effects with either 6S or ATCOR-4,
the latter used in the latest acquisitions. The classification of submerged macrophytes and uncolonised sandy substrates was achieved by the spectral inversion of
the atmospherically corrected MIVIS reflectances. Similarly to Lake Trasimeno,
the spectral inversion was achieved with BOMBER where the implemented
bio-optical model for shallow waters was parameterised with data gathered from
fieldwork activities—in excess of 60 days over 10 years of in situ measurements.
The bottom cover identification has been mapped considering bottom depths
(i.e. those estimated with BOMBER synchronously with retrieval of bottom
types) lower than 7 m, according to Giardino et al. [69], which is the limit of
sensitivity of the model in Lake Garda waters.
Figure 6 shows the distribution of macrophytes in the whole Lake Garda: in the
northern and in the central parts, the presence of macrophytes is small because the
morphological characteristics (slopes descending fast to the lake) are not suitable
for the growth of macrophytes; conversely depth gradients in the southern Lake
Garda facilitate the growth of macrophytes. About 20.5 km
2 of shallow waters
(i.e. bottom depth <7 m) has been mapped: approximately 17 km
2 is characterised
by the presence of macrophytes, even if in some cases sparse.
Figure 7 shows the histogram depicting the height of the water column above the
canopy in the Sirmione Peninsula area (cf. Fig. 6, zoom with the red frame) as
derived by the MIVIS data collected from 1997 to 2011, according to the procedure
described above (for more details refer to Bresciani et al. [67] and Giardino
et al. [69]). The height of the water column above macrophytes is plotted together
with water level fluctuation and water clarity (both derived from in situ measurements); the macrophyte distribution along the littoral zone of the Sirmione Peninsula might be linked to those two physical parameters; thus, the macrophyte change
is then a consequence of both the anthropogenic pressure and meteo-climatic
variations.
72
C. Giardino et al.