single pass stereo, and four to six nadir
spectral bands in the spectral range 400 to
1000 nm. The spectral band widths are to be
less than 10 nm with a dynamic range of
4000:1. The major advances in technology of
such a system compared to existing imagers are
related to the much wider field-of-view
(comparable to that of aerial cameras) and the
improved spatial resolution, which together
provide improved economic viability. In
addition, there are advances in the
digitization rate and signal processing on
board as well as enhanced ground processing
and interpretation optimized for the
application requirements. The conceptual
design of the MEIS FM system has now been
completed and comprises airborne sensor,
ground processor and workstation to provide an
end-to-end system from data acquisition to
product.
WHiRL, airborne Wide-angle High Resolution
Line-imager
As part of the MEIS FM development project at
CCRS, the critical components were identified,
designed and tested. A prototype, WHiRL 191,
comprising these test components was assembled
and was flown first in December, 1989. The
sensor uses a state-of-the-art 6000 element
charge-coupled-device from Loral Fairchild.
In order to obtain a lens of sufficiently
large aperture with an acceptable modulation
transfer function to obtain the required image
uality, a custom lens was designed and
abricated by the National Research Council of
Canada. The signal output is digitized to 12
bit, and recorded on high density digital
tape. By using a data format similar to that
of the MEIS II, existing hardware and software
systems are used to display the imagery and to
transcribe the data on the ground to computer
compatible tapes. Flown at an altitude of 12
km, the sensor has a pixel size of 2.8 m and
a swath of 16.8 km. At an altitude of 1000 m,
the pixel size is .23 m, with a swath of 1.4
km. The details of the sensor and its
performance are published elsewhere (Neville
et al, 1990), but the test flights have shown
the success of this approach, with excellent
image quality and high spatial resolution
obtained across the full field-of-view. The
WHiRL sensor has demonstrated the feasibility
of the high resolution, wide swath digital
imager and has provided some very exciting
imagery. It is an important step in the
measurement of target signatures and in the
development of fully commercial digital
imagers for aerial survey and resource
monitoring.
MEIS calibration
The advances in sensor technology require
parallel advances in calibration and
correction procedures for the data, to allow
the sensor's full capability for signature
measurement to be realized. The multispectral
imager developments at CCRS have been
accompanied by the design and implementation
of an automated calibration facility for the
precision geometric and radiometric
calibration of multi-element array imagers
such as MEIS II (Neville et al, 1990). The
facility, which includes precision optics and
micro-processor based software for control and
data processing, 1s used for the "routine"
annual calibration of the MEIS II. It is also
used in the development of new sensors, to
measure and evaluate the performance of
components such as linear detectors. It was
used extensively in the design and
implementation of the wide-angle imager WHiRL,
both in the alignment of the optical
components and in the characterisation of the
system.
In addition to the development of calibration
procedures, CCRS has ongoing research studies
into the effects of atmospheric conditions and
latform motions on electro-optical imagery,
oth airborne and satellite. The atmospheric
correction algorithms have been developed and
refined over several years, using radiative
transfer modelling, multi-sensor and multi
temporal data acquisition, and validation
procedures (Gauthier at al, 1989). Analytic
algorithms have been specified for image
processing systems, and additional effects,
such as polarization and aerosol optical
depths, are being considered. The improved
understanding of the many processes involved
in image formation, and the ability to correct
for the atmospheric effects, are critical for
the measurement of target signatures on a
quantitative basis.
Geometric corrections, to remove the effects
of platform motion, and particularly aircraft
motion, are also critical for many remote
sensing applications. Georeferenced products
are required for mapping and survey related
activities, and for the increasing
number of resource managers using geographic
information systems. Rigorous photogrammetric
adjustment and geometric correction algorithms
for airborne line imager data have been
developed by Gibson (1986), and have been in
use on the VAX computer system at CCRS to
correct MEIS II and airborne scanner data.
Current activities follow pilot projects to
evaluate the use of MEIS for topographic
mapping, and include the refinement and
transfer of the existing software to operate
on a stand-alone workstation, and the
implementation of algorithms to derive terrain
height from stereo image data and to produce
digital elevation models (Gibson and Bucheit,
1990).
SWIR SPECTRAL IMAGING
Inspired in part by the two relatively broad
short wave infra-red (SWIR) bands on the
Thematic Mapper, there is growing interest in
the SWIR spectral region and spectral
signatures in this region. The remote sensing
interest is concentrated in two resource
areas: vegetation, including forestry, and
geology. While SWIR detector technology has
been under development for at least a decade,
it is within the past 18 months that detectors
with a reasonably large number of elements
have become more readily available. CCRS has
a research project underway to develop a
prototype SWIR sensor and laboratory facility
that will provide signature measurements for
research in the spectral range of 1 to 2.5 urn.
This region has not yet been extensively
researched but offers a number of potential
new applications.
LASER SYSTEM DEVELOPMENTS
The laser systems for remote sensing that were
developed in the past under the research
program of CCRS have now been largely
transferred to the user agencies and
industries. CCRS continues to provide
technical assistance as required to help in
their continuing development and use.
