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The MODIS instrument provides high
radiometric sensitivity (12 bit) in 36 spectral bands ranging
in wavelength from 0.4 µm to 14.4 µm. The responses
are custom tailored to the individual needs of the user community
and provide exceptionally low out-of-band response. Two bands
are imaged at a nominal resolution of 250 m at nadir, with
five bands at 500 m, and the remaining 29 bands at 1 km. A
±55-degree scanning pattern at the EOS orbit of 705
km achieves a 2,330-km swath and provides global coverage
every one to two days.
The Scan Mirror Assembly uses a continuously rotating double-sided
scan mirror to scan ±55-degrees and is driven by a
motor encoder built to operate at 100 percent duty cycle throughout
the 6-year instrument design life. The optical system consists
of a two-mirror off-axis afocal telescope, which directs energy
to four refractive objective assemblies; one for each of the
VIS, NIR, SWIR/MWIR and LWIR spectral regions to cover a total
spectral range of 0.4 to 14.4 µm.
A high-performance passive radiative cooler provides cooling
to 83K for the 20 infrared spectral bands on two HgCdTe Focal
Plane Assemblies (FPAs). Novel photodiode-silicon readout
technology for the visible and near infrared provide unsurpassed
quantum efficiency and low-noise readout with exceptional
dynamic range. Analog programmable gain and offset and FPA
clock and bias electronics are located near the FPAs in two
dedicated electronics modules, the Space-viewing Analog Module
(SAM) and the Forward-viewing Analog Module (FAM) . A third
module, the Main Electronics Module (MEM) provides power,
control systems, command and telemetry, and calibration electronics.
The system also includes four on-board calibrators as well
as a view to space: a Solar Diffuser (SD), a v-groove Blackbody
(BB), a Spectroradiometric calibration assembly (SRCA), and
a Solar Diffuser Stability Monitor (SDSM).
The first MODIS Flight Instrument, ProtoFlight Model or PFM,
is integrated on the Terra (EOS AM-1) spacecraft. Terra successfully
launched on December 18, 1999. The second MODIS flight instrument,
Flight Model 1 or FM1, is inegrated on the Aqua (EOS PM-1)
spacecraft; it was successfully launched on May 4, 2002. These
MODIS instruments will offer an unprecedented look at terrestrial,
atmospheric, and ocean phenomenology for a wide and diverse
community of users throughout the world.
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