International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004 
MULTI-SPECTRAL IMAGER 
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Figure 1: Alsat-1 structure 
Alsat-1 structure is mainly Aluminium. The solar panels, the 
Earth and Space Facing Panels are honeycomb structure. The 
satellite size is 600x600x600 mm with a mass of 98Kg. 
2.1 Payload description 
The Alsat-1 payload is a multispectral camera which works in a 
push-broom mode (forward scan is provided by the spacecraft 
motion). It is in fact a couple of two imagers (of three channels 
each) which work separately or both together. This adds 
flexibility to program images (satellite operations). 
For each spectral band (green, red, near-infrared), two channels 
(from both banks) provide a 600 km swath with (5% overlap 
between them) from its 686km altitude. 
  
Figure 2: Alsat-1 Imager 
2.2 Camera 
It is a line scan camera system designed to provide medium 
resolution (32m GSD), high dynamic range and low noise 
imagery from orbit. It consists of 6 channels split into two 
banks and fixed on a V plate. 
Due to the extremely wide swath, each bank acquires half of the 
scene (with 5% overlap). 
2.3 Channel 
Each channel is in fact an independent camera and contains a 
complete optic-system plus a PCB supporting the sensor & 
linked to the main PCB board in the stack (one main board per 
bank) thanks to a flexi-rigid PCB cable. 
Sensor: lt is a KLI-10203 linear CCD sensor, designed for 
color scanning applications. This is an RGB, 3 channels, 10k 
pixels. Due to the mission requirements, this COTS element 
was requested from Kodak without the RGB organic dye filters 
(applied to the light sensitive areas) but with a multilayer AR 
coated cover glass. 
  
Figure 3: Camera head 
Optics: The lens is a Schneider Apo-Componon HM 150mm 
FL (aperture f/4). Is a flight proven lens (flown onboard 
Tsinghua-l satellite in 2000). This commercial lens has been 
subject to a set of test prior to use. 
Filters: They are high quality dichroic filters in the optical 
assembly provided by BARR Associates Inc.. Due to the 
mission requirement, the spectral band is red [523-605nm], 
Green [629-690nm] and Near Infrared [774-900nm]. The 
spectral characteristics are identical to the Landsat ETM+ bands 
(2,3 and 4) 
Electronic modules: Two boards shares the same PCB module 
(one for each bank of three channels). 
Each board are fully independent and drives the 
three channels (red, green, infrared). It encloses: 
_ An FPGA circuit which is the heart of the module as it plays 
the main role: receives imaging parameters and generates 
signals for CCD sensor, LVDS, ADC...ctc. 
— Three programmable ADC which convert the image signal 
into digital value and send the data via an LVDS to the 
storage modules. 
— A local microcontroller interfaces the board with the OBC 
via a CAN node. 
Each module can be operated individually or synchronised 
together to work in a full 6 channels mode. 
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