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Multiscale Hydrologic Remote Sensing: Perspectives and Applications
Siciliano (SIAS) installed at the center–eastern side of the experimental field with
a meteorological regional information system, which provides hourly independent
measures of the main meteorological variables. They include incoming solar radiation, air temperature, pressure and humidity, wind velocity, and rainfall.
4.4 REMOTE SENSING DATA ACQUISITION AND PROCESSING
The remotely sensed imagery was collected during two distinct periods—in the
spring and summer of 2005 and 2008. In particular, between June and October 2008,
seven high-resolution airborne images were acquired at a height of about 1000 m
above ground level. The instruments onboard the platform were a Duncantech
MS4100 multispectral camera able to acquire images in three spectral bands—green (G;
530–570 nm), red (R; 650–690 nm), and near-infrared (NIR; 767–832 nm) wavelengths—
and a Flir SC500/A40M camera recording the thermal images (TIR, 7.5–13 μm).
The nominal pixel resolution was approximately 0.6 m for visible (VIS)/NIR and
1.7 m for TIR. Figure 4.4 reports the scheduling of all acquisitions (vertical black
lines), overimposed on the temporal trend of daily reference ET (ET 0 , green dotted
line on the left axis) computed by means of the FAO-56 formulation (Allen et al.
1998) and the total daily rainfall (P, blue line on the right axis) as measured by the
SIAS weather station.
The ET 0 analysis highlights a constant maximum atmospheric demand of about
6 mm day –1 in June–July, which linearly decreases to a value of about 3 mm day –1
in October; this variability corresponds to potentially high vegetation stress in the
first period, followed by reduced atmosphere demand in the latter. Two moderate
rainfall events (of about 10 and 25 mm) occurred between the fifth and sixth remote
sensing acquisitions. These events have made different the two latest acquisitions
from the previous overpasses in terms of water availability and potential water stress
conditions.
The G, R, and NIR spectral bands were radiometrically calibrated and atmospheric-corrected by means of the empirical line method (Slater et al. 1996) using
the data collected during in situ campaigns. The in-reflectance images were used to
derive the surface albedo (Price 1990) and NDVI (Rouse et al. 1974). The TIRs were
empirically calibrated to retrieve the surface radiometric temperature by applying
a linear regression between the remotely observed data and in situ measurements,
adopting the NDVI-derived surface emissivity as proposed by Sobrino et al. (2007).
Additionally, to analyze the effects of spatial resolution on the modeled fluxes,
two different data sets were acquired during the spring and summer of 2005: an airborne Natural Environment Research Council (NERC) set of images was acquired
in May, including an Airborne Thematic Mapper (ATM) and a Compact Airborne
Spectrographic Imager (CASI-2) multispectral image, both of which were characterized by high spectral and spatial resolution (3 m); besides, an Advanced Spaceborne
Thermal Emission and Reflection (ASTER) satellite image, acquired in August, was
characterized by three VIS–NIR bands having a 15 m spatial resolution and five
thermal infrared bands with a 90 m resolution.
From a radiometric point of view, the ATM sensor records the incoming radiation
in 11 spectral bands ranging from VIS and NIR (bands 1–8) to shortwave infrared
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
Siciliano (SIAS) installed at the center–eastern side of the experimental field with
a meteorological regional information system, which provides hourly independent
measures of the main meteorological variables. They include incoming solar radiation, air temperature, pressure and humidity, wind velocity, and rainfall.
4.4 REMOTE SENSING DATA ACQUISITION AND PROCESSING
The remotely sensed imagery was collected during two distinct periods—in the
spring and summer of 2005 and 2008. In particular, between June and October 2008,
seven high-resolution airborne images were acquired at a height of about 1000 m
above ground level. The instruments onboard the platform were a Duncantech
MS4100 multispectral camera able to acquire images in three spectral bands—green (G;
530–570 nm), red (R; 650–690 nm), and near-infrared (NIR; 767–832 nm) wavelengths—
and a Flir SC500/A40M camera recording the thermal images (TIR, 7.5–13 μm).
The nominal pixel resolution was approximately 0.6 m for visible (VIS)/NIR and
1.7 m for TIR. Figure 4.4 reports the scheduling of all acquisitions (vertical black
lines), overimposed on the temporal trend of daily reference ET (ET 0 , green dotted
line on the left axis) computed by means of the FAO-56 formulation (Allen et al.
1998) and the total daily rainfall (P, blue line on the right axis) as measured by the
SIAS weather station.
The ET 0 analysis highlights a constant maximum atmospheric demand of about
6 mm day –1 in June–July, which linearly decreases to a value of about 3 mm day –1
in October; this variability corresponds to potentially high vegetation stress in the
first period, followed by reduced atmosphere demand in the latter. Two moderate
rainfall events (of about 10 and 25 mm) occurred between the fifth and sixth remote
sensing acquisitions. These events have made different the two latest acquisitions
from the previous overpasses in terms of water availability and potential water stress
conditions.
The G, R, and NIR spectral bands were radiometrically calibrated and atmospheric-corrected by means of the empirical line method (Slater et al. 1996) using
the data collected during in situ campaigns. The in-reflectance images were used to
derive the surface albedo (Price 1990) and NDVI (Rouse et al. 1974). The TIRs were
empirically calibrated to retrieve the surface radiometric temperature by applying
a linear regression between the remotely observed data and in situ measurements,
adopting the NDVI-derived surface emissivity as proposed by Sobrino et al. (2007).
Additionally, to analyze the effects of spatial resolution on the modeled fluxes,
two different data sets were acquired during the spring and summer of 2005: an airborne Natural Environment Research Council (NERC) set of images was acquired
in May, including an Airborne Thematic Mapper (ATM) and a Compact Airborne
Spectrographic Imager (CASI-2) multispectral image, both of which were characterized by high spectral and spatial resolution (3 m); besides, an Advanced Spaceborne
Thermal Emission and Reflection (ASTER) satellite image, acquired in August, was
characterized by three VIS–NIR bands having a 15 m spatial resolution and five
thermal infrared bands with a 90 m resolution.
From a radiometric point of view, the ATM sensor records the incoming radiation
in 11 spectral bands ranging from VIS and NIR (bands 1–8) to shortwave infrared