waters from Lambro River). For those sites, MIVIS imagery has been acquired
(cf. the table in Fig. 2) and analysed to investigate their water quality, as discussed
in the following paragraphs.
4.1 Data Processing
The processing of MIVIS imagery, used in this study, is performed to correct data
for atmospheric effects and subsequently, for some applications, to retrieve water
quality parameters, substrate types and bottom depth.
The atmospheric correction was achieved with either ATCOR-4 [71] or 6S
(Second Simulation of a Satellite Signal in the Solar Spectrum, vector version
n. 1) [72] codes. ATCOR-4 is an atmospheric correction code used for the atmospheric correction of small and wide Field Of View (FOV) airborne sensors.
ATCOR-4 uses look-up tables generated by MODerate resolution atmospheric
TRANsmission (MODTRAN) [73, 74], relating sensor radiances and albedo for
various atmospheric and geometric conditions. The 6S code is a basic radiative
transfer code which enables accurate simulations of satellite and plane observation,
accounting for elevated targets, use of anisotropic and Lambertian surfaces and
calculation of gaseous absorption. The 6S also performs the atmospheric correction
that, starting from the top-of-atmosphere radiance (or reflectance), allow the atmospherically corrected reflectance to be computed.
The retrieval of the optical properties of water column and bottom from atmospherically corrected imagery was achieved with BOMBER (Bio-Optical Model
Based tool for Estimating water quality and bottom properties from Remote sensing
images), a software package [75] based on the works from [41, 76, 77], which
makes a spectral inversion of bio-optical models for optically deep and optically
shallow waters. Several menus allow the user to choose the model type, to specify
the input and output files and to set all of the variables involved in the model
parameterisation and inversion. The inversion is performed with an optimisation
technique [78] that simultaneously produces the maps of chl-a, SPM, CDOM and,
in case of shallow waters, bottom depth and distributions of up to three different
types of substrate. For both deep and shallow water models, a map of the relative
error involved in the inversion procedure is also given.
In this study, both ATCOR-4 and 6S were run with rural and continental aerosol
models, respectively, and by setting the target’s altitude and the solar-target geometry; in all cases the aerosol concentration (or the visibility range) was derived
from in situ measurements of the aerosol optical thickness. Then, the parameterisation of the bio-optical model implemented in BOMBER was carried out based on
in situ measurements collected in the study areas.
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C. Giardino et al.
(cf. the table in Fig. 2) and analysed to investigate their water quality, as discussed
in the following paragraphs.
4.1 Data Processing
The processing of MIVIS imagery, used in this study, is performed to correct data
for atmospheric effects and subsequently, for some applications, to retrieve water
quality parameters, substrate types and bottom depth.
The atmospheric correction was achieved with either ATCOR-4 [71] or 6S
(Second Simulation of a Satellite Signal in the Solar Spectrum, vector version
n. 1) [72] codes. ATCOR-4 is an atmospheric correction code used for the atmospheric correction of small and wide Field Of View (FOV) airborne sensors.
ATCOR-4 uses look-up tables generated by MODerate resolution atmospheric
TRANsmission (MODTRAN) [73, 74], relating sensor radiances and albedo for
various atmospheric and geometric conditions. The 6S code is a basic radiative
transfer code which enables accurate simulations of satellite and plane observation,
accounting for elevated targets, use of anisotropic and Lambertian surfaces and
calculation of gaseous absorption. The 6S also performs the atmospheric correction
that, starting from the top-of-atmosphere radiance (or reflectance), allow the atmospherically corrected reflectance to be computed.
The retrieval of the optical properties of water column and bottom from atmospherically corrected imagery was achieved with BOMBER (Bio-Optical Model
Based tool for Estimating water quality and bottom properties from Remote sensing
images), a software package [75] based on the works from [41, 76, 77], which
makes a spectral inversion of bio-optical models for optically deep and optically
shallow waters. Several menus allow the user to choose the model type, to specify
the input and output files and to set all of the variables involved in the model
parameterisation and inversion. The inversion is performed with an optimisation
technique [78] that simultaneously produces the maps of chl-a, SPM, CDOM and,
in case of shallow waters, bottom depth and distributions of up to three different
types of substrate. For both deep and shallow water models, a map of the relative
error involved in the inversion procedure is also given.
In this study, both ATCOR-4 and 6S were run with rural and continental aerosol
models, respectively, and by setting the target’s altitude and the solar-target geometry; in all cases the aerosol concentration (or the visibility range) was derived
from in situ measurements of the aerosol optical thickness. Then, the parameterisation of the bio-optical model implemented in BOMBER was carried out based on
in situ measurements collected in the study areas.
68
C. Giardino et al.