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Can you see shadows on clouds?
Further, the sun being beyond the cloud, the bulk of the sunlight reflected by the cloud would fall the wrong way. Long after the sun’s rays are cut off from the spectator, they will still be shining upon clouds high overhead, and therefore able to cast shadows.
What are cloud shadows called?
Sometimes, dark bluish streaks and light beams are observed radiating from the Sun across the purple light. The streaks are the shadows of clouds at or below the horizon and are called crepuscular rays.
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Why are clouds flat underneath?
A: Often low clouds, like stratus and cumulus, appear to have flat bases. These clouds form as air near the ground is rising. As the air rises it expands and cools. So, as a layer of air near the ground rises, the height at which condensation occurs does not vary much and the cloud base height appears uniform.
Do clouds make shadows in the sky?
Yes. If you are in a large landscape on a sunny, windy day when there are clouds in the sky, you’ll see cloud shadows rolling across the hills. When it’s dull and overcast, this is a day when clouds completely block the sun and we are in the cloud shadow all the time.
Is a cloud a liquid or a gas?
While it’s true that clouds contain water, they actually aren’t made of water vapor. If they were, you wouldn’t be able to see them. The water that makes up clouds is in liquid or ice form. The air around us is partially made up of invisible water vapor.
Why clouds are usually white and rain clouds dark?
Clouds usually appear white because the tiny water droplets inside them are tightly packed, reflecting most of the sunlight that hits them. When it’s about to rain, clouds darken because the water vapor is clumping together into raindrops, leaving larger spaces between drops of water.
Is it possible to detect the shadow of a cloud?
For high spatial resolution sensors like Landsat, with only one thermal band and 6 optical bands placed in atmospheric windows, accurate cloud identification is difficult. And, cloud shadow identification is even more difficult. Clouds cast shadows on any type of land cover.
Which is the most accurate Cloud shadow detection algorithm?
For a globally distributed set of reference data, the average Fmask overall cloud accuracy is as high as 96.4%. The goal is development of a cloud and cloud shadow detection algorithm suitable for routine usage with Landsat images.
What kind of sensors are used for cloud detection?
These sensors are usually equipped with more than one thermal band, or with water vapor/CO2 absorption bands, both of which are useful for thin semitransparent cloud detection (Ackerman et al., 1998, Derrien et al., 1993, Saunders and Kriebel, 1998).
Which is the best method to detect clouds in Landsat?
Hégarat-Mascle and André (2009) developed an approach that uses only two bands, Green and Short Wave Infrared (SWIR), to generate a “clear-sky line” and use the distance from the tested points to this line to detect cloud pixels. This method was originally used by Zhang et al. (2002) to correct for haze in Landsat imagery.