388 
After 1986 the MEIS II sensor and 
operations facility were transferred to the private 
sector (Innotech Aviation Enterprises Limited of 
Montreal) where it is now being operated 
commercially (Till, 1987). Since becoming 
available for general use in 1983 demand for data 
from the MEIS sensor has been high for a variety 
of resource applications. Forestry agencies were 
early users of the system and have been and 
continue to be major users (Neville and Till, 1989). 
The MEIS imager uses the "pushbroom" 
scanning approach to image the earth’s surface. A 
linear multi-element array detector is located in 
the focal plane of an imaging lens. The distant 
scene is focused onto the array, and the signals 
generated by each element of the array are 
electronically sampled and digitized, to produce a 
line image in digital format of the scene below. 
As the aircraft moves forward, a new line is 
imaged and sampled, and as this process 
continues, two-dimensional imagery is built up, the 
aircraft motion providing the scanning in the 
forward direction. The spectral content of the 
imaged scene is selected by means of an optical 
filter placed in front of the lens. 
MEIS II has eight spatially registered 
imaging spectral channels, and incorporates 
sophisticated real-time processing to provide 
geometric and radiometric corrections to the output 
imagery. The digital imagery, navigation and 
system data are recorded on tape, for post-flight 
analysis and precision production. The system 
specifications are discussed in detail in a variety 
of papers ( McColl et al, 1984; Till et al., 1986a; 
Till et aL, 1986b). 
3.2 MEIS FM 
The results of applications in forestry 
using the MEIS II sensor have generated 
considerable interest in the potential of a MEIS- 
based airborne system for forestry applications on 
an operational basis. As a result, plans are being 
developed to design and manufacture a new MEIS 
system (MEIS FM) for forestry operation (Neville 
and Till, 1989). The user requirements for the 
advanced linear array imager have been generated 
and system specifications have been prepared and 
matched to the operational survey needs of 
forestry agencies. 
MEIS FM (Multispectral Electro-Optical 
Imaging Sensor for Forestry and Mapping) will be 
a high resolution multispectral imager based on 
state-of-the-art linear array and high resolution 
optics designed specifically for the requirements of 
the forestry and mapping industries. 
The major components of the MEIS FM 
system, from data acquisition to product and 
information system interface, include the airborne 
system, the real-time processor/display and the 
ground processor. The later is being developed as 
a high performance data processing, analysis and 
map generation system based on a supercomputer 
and capable of producing stereo images, digital 
elevation models and topographic maps. 
3.3 FLI History and Description 
The FLI (Florescence Line Imager), which 
is based on linear array technology similar to that 
of the MEIS sensor was developed by Moniteq Ltd. 
of Concord, Ontario in conjunction with Itres Ltd. 
of Calgary, Alberta for the Department of 
Fisheries and Oceans. The FLI system, also 
known as the Programmable Multispectral Imager 
(PMI) due to its unique ability to reconfigure its 
spectral bands, is a programmable imaging 
spectrometer and line imager that has been 
operating for various research studies since 1984. 
In 1986 a two year loan of the FLI to Moniteq 
was arranged, and this company has since made 
the instrument commercially available to remote 
sensing users (Gower, 1988). 
The FLI system evolved from a need to 
monitor ecological effects in lakes and coastal 
waters, and for determining water quality. This 
was accomplished by designing a system which 
could image ocean chlorophyll fluorescence and 
spectral reflectance change in water caused by 
phytoplankton (Hollinger et al., 1987). 
The FLI is an imaging spectrometer that 
makes use of a two-dimensional multi-element 
array of detectors in the focal plane of a dispersive 
optical system. Light from a swath line on the 
ground is collected by the objective lens, dispersed 
by a grating into a spectrum, and focused onto the 
array. The across-track spatial information falls 
along one dimension, and spectral information 
from each pixel is registered along the other 
dimension. The system can operate in two modes. 
In the "spatial mode", the system can perform high 
spatial resolution mapping by forming pushbroom 
images in 8 spectral bands. Alternatively in the 
"spectral mode", the system can provide low spatial 
resolution mapping in 288 spectral bands, with 40 
pixels located across the swath. 
3.4 CASI History and Description 
More recently the CASI (Compact Airborne 
Spectrographic Imager) system has been developed 
by Itres Ltd. as a downsized version of the FLI 
system. The CASI system is a personal computer 
sized second generation instrument which is 
flexible and portable. The real time display and 
data review on the instrument itself allows for 
easy checks of data quality, and combined with 
processing on personal computers facilitates rapid 
turnaround of data (Borstad et al., 1989). 
A unique feature of the CASI "spectral" 
mode is a co-registered monochromatic spatial 
image acquired at the same time as the spectral 
data. This image, termed the ‘track recovery