General descriptions
Components:
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Optical head : a system of 2 parabolic mirrors, focalizing the sky onton 1 photodiode, using 1 central mask to:
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Obtain alternating FOV 25° - 50 °
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Reduce specular scattering of dust cover on optical system
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Electronics : 8-decade logarithmic amplification, converting photodiode current to output voltage, temperature compensated, to work with:
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Both direct solar intensity and twilight intensity
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Martian temperature variation from -120°C to 50°C
NETLANDER specifications
General specifications:
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Number of channel : 2
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Mass : 90g (25g×2 optical head + 20g×2 electronics, cables not included)
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Comsomation : 30mW
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Data rate : 2kb/day
Figure 1. Mechanical and optical layout of optical head of ODS in NETLANDER version of two channels: (1) upper parabolic mirror and entrance pupil, (2) lower parabolic mirror, (3) black wall, (4) black central mask, (5) silicon photodiode, (6) temperature sensor, (7) micro-porous pressure equalizer, (8) coaxial cables, (9) sunlight path.
Photodiode:
Electronics:
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Typical transfer function (CSVdata)
Figure 2. Typical electronics transfer function, from photodiode current (A) to output voltage (V), with varying temperature (from -50°C to 50°C). Between range of -3V to 3V, the output is nearly linearly dependent on logarithm of current and independent with temperature; except for temperature as high as 50°C and low current (observation at night, rarely with temperature as high).
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Typical inversed transfer function (CSVdata)
References
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Maria, J.-L., Tran, T.T., Pommereau, J. P. et al., Technical aspects of the optical depth sensor, Advances in Space Research, accepted.
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