Specifications

Background
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system. The optical bench is currently used to test performances of the wide angle CCTV
lens of the ALMASat-1 sun sensors. Procedures has been developed to retrieve the exact
distortion function of optical system.
In the following pictures some examples of the spot shape on the optical axis (a), at
30° of hFOV (b) and near the full field (c) of the 130° wide angle lens.
(a)
(b)
(c)
Figure 7: Spot shape of the ALMASat-1 Sun Sensor wide angle lens used as test bed for the
develpment of the calibration procedures for the AMSC
The camera electronics is currently under development and a preliminary layout is
shown in Figure 8. The CCD will be controlled by a flexible FPGA (currently under test a
Xilinx Virtex 5) that can be customized to use a variety of different sensors. The filter
will be connected to a proprietary box linked to the FPGA via RS-232 interface. The
entire system will be managed by a platform based on an ARM7 microprocessor able to
store images in a commercial flash memory drive and also send data via CAN BUS to the
S-band transmitter. Each image acquired by the sensor is currently in the order of 50
Mbit for a single band image, thus the use of an appropriate compression algorithm is
necessary. One of the most flexible algorithms that can be used on-board to reduce the
image dimensions is the JPEG2000, the new international standard for image data
compression which uses latest compression techniques based on wavelet technology.
The JPEG2000 provides for both lossless or lossy compression in the same
architecture with different compression ratios. Compression ratios usually vary between
2:1 in lossless mode to 15:1 in lossy mode with unnoticeable artefacts, allowing further
use of the images for analysis.