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Multiscale Hydrologic Remote Sensing: Perspectives and Applications
10.3.4 ModeRate ReSolution iMaging SPectRoRadioMeteR
In recent years, the moderate resolution imaging spectroradiometer (MODIS) satellite sensor has been used in a number of studies and gained widespread acceptance
(Gao et al. 2010a,b; Parajka and Blöschl 2008a,b; Hall and Riggs 2007; Salomonson
and Appel 2004; Gillan et al. 2010; Molotch and Margulis 2008; Dozier et al. 2008;
Homan et al. 2011). This is particularly true in view of the importance and benefits
inherent in accurate estimation of snow cover extent for modeling snowmelt runoff
processes associated with climate change scenarios.
MODIS, an image spectroradiometer, is one of the advanced satellite sensors
that employ a cross-track mirror, collecting optics, and a set of individual detector elements to provide imagery of the earth’s surface and clouds in 36 discrete,
narrow spectral bands from approximately 0.4 to 14.0 μm (Barnes et al. 1998). As
the most comprehensive Earth Observing System (EOS) sensor designed by the
National Aeronautics and Space Administration (NASA), MODIS has a combination of unique features, including the ability to observe measurements at three
spatial resolutions on a daily basis and a wide field of view. For example, the
MODIS snow product (MOD 10) creates automated daily, 8-day composite, and
monthly regional and global snow cover maps (Ault et al. 2006). Furthermore,
the spatial resolution of the MODIS instrument varies with the spectral band and
ranges from 250 m to 1 km at nadir (Hall et al. 2002). These distinct features
enable it to monitor a variety of geophysical products on the earth’s surface on
a daily basis in contrast to Landsat’s enhanced thematic mapper plus (ETM+),
which can only image a given area of the earth’s surface once every 16 days.
The MODIS instruments are mounted on two satellites, Terra and Aqua. Terra,
the first EOS satellite, was launched on 18 December 1999 and commenced observations in February 2000 (Parajka and Blöschl 2008b). Aqua, the second EOS satellite,
was launched on 4 May 2002 (Gao et al. 2010b) and started the observations in the
same year. The two satellites convey the same type of MODIS instruments, but they
differ in their local equatorial crossing time. While Terra passes from north to south
across the equator in the morning (around 10:30 a.m.), Aqua passes from south to
north over the equator in the afternoon (around 1:30 p.m.).
The global daily snow cover product is provided through the Distributed Active
Archive Center of the National Snow and Ice Data Center (NSIDC). The snow maps
are gridded in equal-area tiles in a sinusoidal projection. Each tile consists of a
1200 km × 1200 km data array, which corresponds to 2400 pixels × 2400 pixels at
a 500-m resolution (www.nsidc.org). In addition to the 500-m resolution, snow maps
are also available at 0.05° and 0.025° resolutions on a latitude/longitude grid known
as the climate-modeling grid (Halls and Riggs 2007; see Figure 10.2).
MODIS snow cover data are based on a snow mapping algorithm that employs
a normalized difference snow index (NDSI; www.nsidc.org). Through the strong
reflectance in the visible and the strong absorption capacity in the shortwave infrared
part of the spectrum, the NDSI makes it possible to differentiate snow from other surface features (Parajka and Blöschl 2008b). The spectral signatures of clouds and snow
can be similar. As a result, snow/cloud discrimination with MODIS is not always
reliable (Dozier et al. 2008). Nevertheless, snow and cloud discrimination is based on
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
10.3.4 ModeRate ReSolution iMaging SPectRoRadioMeteR
In recent years, the moderate resolution imaging spectroradiometer (MODIS) satellite sensor has been used in a number of studies and gained widespread acceptance
(Gao et al. 2010a,b; Parajka and Blöschl 2008a,b; Hall and Riggs 2007; Salomonson
and Appel 2004; Gillan et al. 2010; Molotch and Margulis 2008; Dozier et al. 2008;
Homan et al. 2011). This is particularly true in view of the importance and benefits
inherent in accurate estimation of snow cover extent for modeling snowmelt runoff
processes associated with climate change scenarios.
MODIS, an image spectroradiometer, is one of the advanced satellite sensors
that employ a cross-track mirror, collecting optics, and a set of individual detector elements to provide imagery of the earth’s surface and clouds in 36 discrete,
narrow spectral bands from approximately 0.4 to 14.0 μm (Barnes et al. 1998). As
the most comprehensive Earth Observing System (EOS) sensor designed by the
National Aeronautics and Space Administration (NASA), MODIS has a combination of unique features, including the ability to observe measurements at three
spatial resolutions on a daily basis and a wide field of view. For example, the
MODIS snow product (MOD 10) creates automated daily, 8-day composite, and
monthly regional and global snow cover maps (Ault et al. 2006). Furthermore,
the spatial resolution of the MODIS instrument varies with the spectral band and
ranges from 250 m to 1 km at nadir (Hall et al. 2002). These distinct features
enable it to monitor a variety of geophysical products on the earth’s surface on
a daily basis in contrast to Landsat’s enhanced thematic mapper plus (ETM+),
which can only image a given area of the earth’s surface once every 16 days.
The MODIS instruments are mounted on two satellites, Terra and Aqua. Terra,
the first EOS satellite, was launched on 18 December 1999 and commenced observations in February 2000 (Parajka and Blöschl 2008b). Aqua, the second EOS satellite,
was launched on 4 May 2002 (Gao et al. 2010b) and started the observations in the
same year. The two satellites convey the same type of MODIS instruments, but they
differ in their local equatorial crossing time. While Terra passes from north to south
across the equator in the morning (around 10:30 a.m.), Aqua passes from south to
north over the equator in the afternoon (around 1:30 p.m.).
The global daily snow cover product is provided through the Distributed Active
Archive Center of the National Snow and Ice Data Center (NSIDC). The snow maps
are gridded in equal-area tiles in a sinusoidal projection. Each tile consists of a
1200 km × 1200 km data array, which corresponds to 2400 pixels × 2400 pixels at
a 500-m resolution (www.nsidc.org). In addition to the 500-m resolution, snow maps
are also available at 0.05° and 0.025° resolutions on a latitude/longitude grid known
as the climate-modeling grid (Halls and Riggs 2007; see Figure 10.2).
MODIS snow cover data are based on a snow mapping algorithm that employs
a normalized difference snow index (NDSI; www.nsidc.org). Through the strong
reflectance in the visible and the strong absorption capacity in the shortwave infrared
part of the spectrum, the NDSI makes it possible to differentiate snow from other surface features (Parajka and Blöschl 2008b). The spectral signatures of clouds and snow
can be similar. As a result, snow/cloud discrimination with MODIS is not always
reliable (Dozier et al. 2008). Nevertheless, snow and cloud discrimination is based on