High Spatial Resolution Digital Imagery
through configuration files. The 384 spatial pixels include 360 ground-target and
20 downwelling irradiance pixels.
Mode A. Provides full spatial (384) and full spectral (288 pixels) information.
Neither spectral channel bandwidth modification nor spatial binning is available,
but each pixel of the focal plane is digitized as single pixel. Therefore, mode A
demonstration. However, it can be used in low velocity or high-altitude aerial
Mode B. Provides full spatial resolution (i.e., smallest pixels) with reduced
spectral resolution. This mode offers 384 spatial pixels with no binning, although
spatial binning (i.e., summing of 2, 4, or 8 pixels to output larger pixels) is
available for low signal level measurements.
Spectral sampling is programmable between 1.5- to 9.4-nm bandwidths
within a total wavelength range of 450 nm. Individual spectral bands are pro-
grammable. Therefore, the total number of channels is controlled by the selected
spectral bands and selected bandwidths.
Mode C. Provides full spectral resolution, with reduced spatial resolution.
This mode uses the full hyperspectral capabilities of the sensor (288 bands), but
with only 47 pixels in the cross-track direction (as compared to 384 with Mode
B). Further spatial binning (i.e., decreased spatial resolution) is still available.
Mode C is suitable for hyperspectral applications that require varied spatial
Mode D. Provides the greatest variation in both spectral resolution and spatial
resolution. While Mode D minimizes the amount of data to be collected and
allows high frame rates, it does not offer the highest spatial resolution.
Downwelling irradiance measurement
The quality of airborne hyperspectral remotely sensed data is enhanced by
using downwelling irradiance measurements together with the actual target
measurements. In AISA this is implemented using a hemisphere (or flat) reflector
attached to the aircraft roof receiving direct solar radiation. In the best case, there
is a clear, sunny sky. The correction is more difficult if atmospheric conditions
are cloudy or partly cloudy. The resulting signal is fiber-optically connected to
the spectrograph such that it covers a few pixels from the swath width (i.e., a few
columns on the detector). Thus, there is a simultaneous measurement of down-
welling irradiance with the same wavelength range as is captured by the ther-
moelectrically stabilized charge-coupled device (CCD). This is a great advantage
to systems requiring mechanical movement of the instrument or even a separate