30. HYPERSPECTRAL IMAGER SURVEY AND DEVELOPMENTS
FOR SCIENTIFIC AND OPERATIONAL LAND PROCESSES
MONITORING APPLICATIONS
319
HRIS) following the disperser, and focusing the dispersed beams onto
the detector array, often containing some corrective elements for focal
plane curvature correction, aberration or slit curvature correction—a rather crucial sub-unit; as indicated above, the spectral disperser could be
transmissive, reflective or holographic gratings (all with spectral range
limitations and/or low optical throughput), or single or dual prisms
The Focal PlaneAsembly (FPA), consisting of the linear (whiskbroom) or
2-d (pushbroom) detector array(s), its mounting, cooling for IR, and analogue control and readout electronics, plus the HRIS SWIR Array. For
unit, at least for the higher resolution instruments with often over 200
spectral channels. Together with some additional control electronics,
these systems provide for line frequencies above 100 Hz and pixel rates
(at the FPA output channels) of the order of 5 Mpixels/s. The
corresponding internal data rates often exceed 300 Mbps, requiring online data correction (calibration), channel and resolution selection and
data compression—for space versions rad-hard. Fig. 4-4 schematically
shows a generic digital signal processing electronics.
wavelengths
silicon detectors can no longer be used, this is
where IR detector array technology has to be introduced. For linear
arrays of a whiskbroom IS, there is quite a choice. For 2-d arrays of
pushbroom instruments, either narrow-band InGaAs type lattice
materials with GaAs multiplexers can be used, or low-responsivitiy Si:Pt
(or-:Pd) Schottky Barrier arrays with Si MUXes, or hybridized InSb
arrays (HYDICE) or CMT (HgCdTe) ir diode arrays mated to a Si
MuUX, as for HRIS. For technical reasons (CTE matching between
MUX and IR detector material), the number of spatial elements is
limited to 256 or at the most 512 pixels for a monolithic array, thus,
optical or mechanical butting techniques have to be applied, which
makes these arrays a costly item. Another problem is for MUX layout
the low photon number in SWIR on one hand, asking for very small
injection capacitances, and the high dynamic range and charge handling
capacity.
Note that IR detector arrays (including SWIR) require cooling, either by
a passive radiator cooler (MODIS, HRIS) or by active Stirling coolers
(PRISM). Furthermore, their location is not indifferent: they need cold
space viewing, which must be taken into account in the optics design.
See Fig. 5 (PRISM) as an example.
All these units are typically accommodated on a common optical bench
in the optics module housing, including thermal control and harness
The digital processing electronics also represents a rather critical sub-
FOR SCIENTIFIC AND OPERATIONAL LAND PROCESSES
MONITORING APPLICATIONS
319
HRIS) following the disperser, and focusing the dispersed beams onto
the detector array, often containing some corrective elements for focal
plane curvature correction, aberration or slit curvature correction—a rather crucial sub-unit; as indicated above, the spectral disperser could be
transmissive, reflective or holographic gratings (all with spectral range
limitations and/or low optical throughput), or single or dual prisms
The Focal PlaneAsembly (FPA), consisting of the linear (whiskbroom) or
2-d (pushbroom) detector array(s), its mounting, cooling for IR, and analogue control and readout electronics, plus the HRIS SWIR Array. For
unit, at least for the higher resolution instruments with often over 200
spectral channels. Together with some additional control electronics,
these systems provide for line frequencies above 100 Hz and pixel rates
(at the FPA output channels) of the order of 5 Mpixels/s. The
corresponding internal data rates often exceed 300 Mbps, requiring online data correction (calibration), channel and resolution selection and
data compression—for space versions rad-hard. Fig. 4-4 schematically
shows a generic digital signal processing electronics.
wavelengths
silicon detectors can no longer be used, this is
where IR detector array technology has to be introduced. For linear
arrays of a whiskbroom IS, there is quite a choice. For 2-d arrays of
pushbroom instruments, either narrow-band InGaAs type lattice
materials with GaAs multiplexers can be used, or low-responsivitiy Si:Pt
(or-:Pd) Schottky Barrier arrays with Si MUXes, or hybridized InSb
arrays (HYDICE) or CMT (HgCdTe) ir diode arrays mated to a Si
MuUX, as for HRIS. For technical reasons (CTE matching between
MUX and IR detector material), the number of spatial elements is
limited to 256 or at the most 512 pixels for a monolithic array, thus,
optical or mechanical butting techniques have to be applied, which
makes these arrays a costly item. Another problem is for MUX layout
the low photon number in SWIR on one hand, asking for very small
injection capacitances, and the high dynamic range and charge handling
capacity.
Note that IR detector arrays (including SWIR) require cooling, either by
a passive radiator cooler (MODIS, HRIS) or by active Stirling coolers
(PRISM). Furthermore, their location is not indifferent: they need cold
space viewing, which must be taken into account in the optics design.
See Fig. 5 (PRISM) as an example.
All these units are typically accommodated on a common optical bench
in the optics module housing, including thermal control and harness
The digital processing electronics also represents a rather critical sub-