Sunrise as seen from a satellite


How does sunrise look like from a satellite’s perspective? This might seem like a pretty boring question – after all we all know images like this one and this one which show sunrise in some form as seen from space. But i here mean of course how does sunrise look like for an earth observation satellite. Recording sunrise views is obviously not a normal task for such satellites but generally at the edge of the polar night all earth observation satellites can in principle record sunrise.

The following image is a Landsat view from August showing sunrise at the end of the winter at the east of the Antarctic peninsula. I have shown several images with a low sun position and long shadows from the Antarctic before but never a true sunrise or sunset.

At the top of this image the sun is about 1-2 degrees above the horizon leading to long shadows but still clearly visible light on the flat ice shelf areas.

As you move southward the sun is moving towards the horizon leaving only the tops of the mountains sunlit.

At the bottom the sun is still below the horizon and even the mountains are only lit by the skylight, i.e. light scattered by the atmosphere that is coming primarily from the north indicating the approaching sun.

What you can also see in this last crop is well visible noise in the dark parts. The satellite’s sensor is of course designed to record the bright sunlit earth surface and these areas reflect only a very small fraction of usual amount of light in this situation. If you are into photography a bit you might know that directly before sunrise or after sunset you have – depending on the circumstances – light levels on the order of 10 EV or a factor of 1000 less than in direct sunlight during midday. Considering such a satellite cannot vary either exposure time or aperture to compensate for different light levels the results are actually quite remarkable. The large scale structures visible in the noise in direction of the satellite path result from the satellite sensor being made from several separate modules which have slightly different noise characteristics.

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