星敏感器白天观星的对比度分析

Analysis of the Contrast of Star to Sky Background During Daytime for Star Sensor

恒星-背景对比度是星敏感器白天探测恒星的一个重要参数,它决定了星敏感器可探测星等的极限值。叙述了恒星-背景对比度的计算方法,分析了星敏感器在3°×3°视场角和0°与40°两个观测角下,6等K和M型恒星的对比度随观测高度、太阳天顶角、波段和恒星光谱类型的变化特征。结果表明:对比度随观测高度的增加按指数增加,40km高度上的对比度是10km上对比度的100倍左右;随太阳天顶角的增加按线性增加,长波波段上80°太阳天顶角的对比度是20°时的6倍左右;经过滤波片(B+W 090)滤光的全波段(0.4～1.0μm)上的对比度和0.6～0.7μm分波段的对比度较接近;全波段上的对比度随恒星光谱类型几乎不变化。这些结果可用于星敏感器在大气层内白天观测恒星的星等极限估计。

Contrast of star to sky background is an important parameter of star sensor. It determines stellar magnitude detecting limit of the star sensor. Method for calculating the contrast of star to sky background is described. For a star sensor with 3° × 3° field of view, 0° and 40° observing angle to detect 6.0 magnitude stars of K and M types, the contrast of star to sky background is calculated as a function of observing height, solar zenith, wave band, and stellar spectral type. Results show that the contrast increases exponentially with increasing of observing height, and the value at 40 km altitude is about one hundred times of that at 10 km altitude. The contrast also increases nearly linearly with increasing of solar zenith,and the value at solar zenith of 80° is about six times of that at solar zenith of 20° for longer wavelength. The contrast in 0.4～1.0 μm spectral range by using B＋W090 filter is close to that of 0.6～0.7 μm waveband, and the contrast of the whole waveband almost doesn＇t vary with stellar spectral types. The results can be used for estimating stellar magnitude detecting limit of the star sensor in the atmosphere during daytime.