Abstract:
AVNIR is a high spatial resolution optical sensor for observing land
and coastal zones in visible and near-infrared regions. AVNIR has 4
spectral bands with a 16m spatial resolution and 1 pachromatic band
with an 8 m spatial resolution. The AVNIR data will be useful for
environmental awarenenn and monitoring of such phenomena as
desertification, destruction of
... tropical forests, and pollution of
coastal zones as well as for resource exploration, land use, etc.
AVNIR's field of view (FOV) is about 80km, picked up by lines of small
pixels. Its FOV scans the entire earth's surface as the satellite
moves. There are only a few other similar sensors, such as TM on
LANDSAT. Among AVNIR's sensors are features which give the sensors
high spatial resolution, a pointing function to change the observation
field by +-40 degrees along the cross track, a 0.4rim band useful for
coastal zones and lakes, an optial calibration function which uses
solar light and lamps, as well as others.
AVNIR is composed of two units, the Scanning Radiometer Unit (SRU)
which is mainly composed of optical components and the Electronic Unit
(ELU) which includes mainly electronic components. Optics in SRU
adopts a Catadioptric Schmidt optical system to reduce aberration in a
wide field of view. Large mirrors used in Optics and Pointing
Mechanism Assembly are ultralight mirrors weighing 50 to 70% less than
converntional mirrors, made from low expansion material. CFRP with low
thermal and moisture expansion properties is used as the truss
structural material in order to make Optics light yet extremely
precise in orbit. The large linear-array CCDs with 5,000 and 10,000
pixels are used as detectors and deliver high spatial resolution.
Observation data is compressed in the Image Processing Assembly by
about 10% in order to reduce the transmission data rate. 
