An Artistic Approach to Satellite Imagery
Using Sentinel Hub EO Browser and custom scripts
A guest blog post by Rafal Wereszczynski
Foreword by Sentinel Hub
Welcome to our Sentinel Hub Medium guest blog post series! As an integral part of our vibrant community, we are are delighted to bring you the diverse perspectives and insights of our valued users. Each post in this series represents the unique experiences, expertise and creativity of individuals harnessing the power of Sentinel Hub services. From innovative applications to ground-breaking research, these guest blog posts offer a glimpse into the myriad ways our users are leveraging satellite imagery and data to explore, analyse and address real-world challenges. We’re excited to provide this space for our community to share their stories and inspire others on their journey with Sentinel Hub.
My adventure with satellite imagery began about three years ago. I have been interested in cosmos and deep space missions for many years and I’ve been paying attention to many aspects of modern space exploration. Of course, watching hundreds and hundreds of stunning images taken by various space probes has been an important part of it.
Every now and then I was looking at some images taken by Earth Observation satellites and I started to become more and more interested in that particular area of space exploration. At some point I found myself spending whole hours just staring at all kinds of pictures of our planet.
Soon it became clear to me that right next to large official organizations like NASA or ESA there is a large community of ordinary people who do image processing and share their own work on social media. I felt that this was something I wanted to do.
I got curious, so I started to look for data. I didn’t have any experience in satellite imagery, so using the data I found was quite difficult, but that suddenly changed when I discovered Sentinel Hub and EO Browser. The combination of easy access, many data sources, and a variety of predefined views has made using the website a very pleasant experience and pushed me to become a daily guest.
Having some experience in painting and digital arts naturally steered me towards looking for ways to make all those images more visually pleasing and, if possible, to bring out some interesting details out of the scenes. This is where custom scripts came in.
Today I’m using scripts on a daily basis, constantly working on new ones and improving the ones I’ve made before in order to achieve the desired effects.
The main goal of my work is to find interesting scenes and try to focus on their important elements. Whether it’s a volcanic eruption, an interesting landscape, a hurricane, or just some cloudy weather — almost every time some aspect of the scene seems more important than the rest. I think that identifying it, bringing it out, and attempting to tell some kind of story is the key.
Below are some image examples representing different processing methods and the ideas that stood behind them. In order to help better understand how they work, EO Browser links with all of the scripts used to create the images can be found at the very bottom of this post. I’m also using GIMP as an external software to do some post-processing, but only for some gentle finishing touches — the goal is to achieve as much as possible through relatively simple scripts in EO Browser.
For those who have very little or no experience in using JavaScript, I highly recommend watching the tutorial created by the Sentinel Hub team. It provides all of the basic knowledge needed to get started and turned out to be very helpful to me when I was just a beginner.
The meaning of color
Hurricanes are some of the most powerful natural events on the planet. Their size and the fact that they spend most of their lives over the water makes them perfect targets for Sentinel-3 SLSTR.
Using SWIR bands creates a high contrast between the clouds and water. There is also a small brightness difference between those bands — taking advantage of that difference and mapping it to colors can turn a desaturated image into a rather striking view.
We can also use colors to express some general properties like storm category, its size, or proximity to inhabited areas. Let’s take a quick look at those two cyclones shown above — I think that most viewers can easily guess which one of them was more dangerous at the time. Sometimes all that’s needed is picking the right color.
The glow
Volcanoes are my favourite targets, right from the moment I saw my first satellite images of a volcanic eruption in Iceland in early 2021. That event pushed me towards using custom scripts in the first place. I became very curious about how much detail and information can be extracted from those images and soon after that, I started to write my own scripts. Over time I have developed my own distinct style, which I like to call “The glow”.
Just like hurricanes, volcanic eruptions are among the most powerful natural events. Most satellite images use infrared bands to show immense heat associated with eruptive activity and they usually use those bands in chromatic order, resulting in red, yellow, and sometimes a little bit of white. In the case of an active volcano, the source of IR signal is emission and not reflectance, so it was easy to connect that property with a lightbulb or black body radiation. As things get hotter their glow starts to shift from red to yellow, then white and eventually to blue. I wanted to make my lava flows feel even more hot and energetic, so I came up with this yellow and white shine, which became a kind of my “trademark”.
The importance of context
Context also matters — two eruptions depicted above took place in inhabited areas, causing damage to the local population. Therefore I decided not to use pleasant, warm, and saturated colors for the surrounding land — in those particular cases, grey and blue felt more appropriate. It also made those lava flows really stand out against darker surroundings.
Clouds have been, are, and always will be frequent guests on images collected by optical sensors. They are often treated as an enemy and sometimes can be a source of frustration. However, since there is nothing we can do about them, we have to accept their presence and try to make some use of them if possible. The image above is an example of that approach — the area was covered by some clouds, surrounding an active volcano crater. Subtracting the water vapour band from the image resulted in a pretty nice view consisting mostly of the SWIR signal emitted by the hot lava. This time infrared glow is more red in order to simulate some kind of nighttime view.
Electric blue
I like to look at storm clouds from above, so naturally I wanted to figure out an interesting way to show them. Adding some of the cirrus band to the blue channel allows us to highlight the upper parts of convection cells and gives them this “electric” blue hue. It can look a little bit like a lightning strike that got caught by the sensor.
There’s no reason to stick only to blue — e.g. adding some of the cirrus band to the red and green channels can give upper-level clouds some warm “sunset” or even “fiery” look. This simple trick works really well for long, feathery cirrus clouds and can harmonize nicely with snow-covered areas.
Color enhancement
Taking advantage of small differences between reflectance in different wavelengths can be really helpful in bringing out some delicate, naturally occurring tones. In case of relatively bright scenes, like the one shown above, non-linear dimming can also be used in order to better define structures.
First, the natural RGB ratio was changed in favour of blue by using a slightly darker NIR band in the red channel and visible red in the green channel. Then, the general brightness was decreased by multiplying each of this NIR-Red-Blue set of bands by the regular visible Red, Green and Blue bands.
Adding color differences to selected channels is another way to enhance color. In this case, the relatively small difference between red and blue visible light was added to the red channel in order to exaggerate the natural redness of the rocks. That small difference in brightness wasn’t big enough to have the desired impact on the final image, therefore it was multiplied by a factor of three. The next step was to ensure there were no negative values, in places where blue may have been brighter than red. Of course, other differences and other channels can also be used.
Similar to adding or subtracting differences in brightness, RGB color ratio can also be used to enhance colors. We can get our color ratios by simply dividing red by green, green by blue, etc. Depending on the amount of ratios used in the process our result colors can range from subtle to vivid.
Natural color
Nature often gives us striking views for free, so it’s worth using them. Not every image has to be heavily processed in order to attract our attention. Sometimes all of the key elements are already in place and all else is just cosmetic — small contrast adjustment, maybe a little bit of extra saturation, some deeper shadows and the final image is ready. In those cases the most important thing can be choosing the composition — some scenes will look better when the important element will be placed at the center and in other cases the best way to go is revealing just a part of it, leaving the rest to the viewer’s imagination.
Custom scripts in Sentinel Hub EO Browser are truly powerful tools — in the hands of amateurs even simple ones can transform ordinary satellite images into quite captivating views. All you need is some basic understanding of color, composition, and math, combined with curiosity and a little bit of patience.
When used by professionals and scientists, custom scripts have the potential to significantly improve data visualization, to make scientific projects more attractive and possibly to help reach a greater audience. I would like to encourage everyone to try using them.
For those who would like to see some more of my images or ask me any questions, I recommend visiting my profile on X (old Twitter).
References
To learn more about custom scripts, watch the following webinar. Also, visit the Sentinel Hub webinar page for more insights on similar topics.
Custom scripts used to create images included in this post (in order of appearance):
