Interactive cloud frequency web map, with Google Earth Engine
Summary:Â I’ve developed an interactive cloud frequency map, available here. It may be particularly useful for satellite imaging researchers working out where they can acquire imagery easily.
One of the major issues with optical satellite imaging is that you can’t see through clouds: so normally when its cloudy, you can’t get anything useful from your images. This actually has a big effect on where you can use satellite imaging effectively: for example, a lot of people have used satellite data to monitor changes in the Amazon rainforest, but it’s quite challenging to find cloud-free images due to the climate in that region of the world.
Similarly, I remember a friend of mine struggling throughout his PhD with cloud cover. He was trying to observe vegetation in India, and needed to look at images taken around the monsoon because the vegetation was growing most vigorously at that time of year. The problem, of course, is that its very cloudy during the monsoon season – so there were barely any images he could use, and he ended up spending half of his PhD developing a new method to classify cloud from his images, so that he could extract the small fraction of the data that was actually usable.Â I’ve run into similar problems too – for example, some research in Hydrabad ran into problems caused by the limited availability of data due to cloud cover.
I’ve often found myself wanting to look at cloud frequency in different areas so that when I have a number of options for where to use as a case study for something, I can easily pick the area that is likely to have the most cloud-free data available. I’ve been a ‘Trusted Tester’ of Google Earth Engine for a long time, and had written a short script in Earth Engine to produce a map of cloud frequency.
So, I hope you find this useful (and even if you’re not using it as a satellite imaging researcher, you may find the cloud cover patterns across the world to be fascinating anyway…)