 # Processing of sentinel-2 images using ESA's SNAP

I want to calculate turbidity from reflectance of sentinel-2 image using SNAP.

But I don’t know which tool to use.

The turbidity calculation formula uses the probability.

I also want to create a contour diagram based on reflectance, but I don’t know how.

Please tell me who you are.

Maybe you can include links to what you are referring to so we can get an idea what you mean.
I’m not an expert on aquatic remote sensing, but I suppose that there are many approaches on this.

you speak of a turbidity calculation formula - where is it from?

Also where you have seen this “contour diagram based on reflectance”. It would ne nice to see an example what you mean.

I’m sorry.

I should have narrowed down what I wanted to know.

Regarding turbidity, I asked if there is a function that can create a figure by entering an arbitrary expression with snap.

I really want to know if there is a function to create contour diagrams.

you can apply equations to rasters by right-clicking them and select “Band Maths”. I’m not aware of a linear function that retrieves turbiditiy from a reflectance image, sorry.

Do you have an example for a contour diagram? I’m afraid I don’t have an idea how this could look for a multi-spectral image. Maybe you can refer to an external image which shows something similar.

Is a [Band Math] calculated by reflectance or a radiance value?

An example of a contour diagram is like a site in a hyperlink.
contour diagram

For most empirical models, it is better to use the reflectance because it is calibrated.

The maps you linked show some sort of classified thematic map, but I don’t understand the language. Please have a look at SNAP’s “Thematic Land” and “Thematic Water” processing toolboxes and check if some of them come closer to what you need.

Thank you for repeated replies.

then you might find these turorials helpful:

You can calculate the band, but I think the image generated after that will be the image of the luminance value.

Is there a way to display an image other than the luminance value after calculating the band?

For example, generating a colored image based on the calculated reflectance for each pixel.

You create RGB images by right-clicking on the product. I really don’t understand what you want, sorry.

How do I check the reflectance after band calculation?

Is there a way to show the change in reflectance for each longitude and latitude?

you can either use scatter plot to plot reflectance against the latitude (tie-point-grid) or use the profile tool to plot the reflectance along a line.

When I draw a line where I want to display the reflectance, can I draw a line by entering the latitude and longitude numerically?

For example, while the longitude is fixed, the latitude is 35 to 40.

I don’t know of this option, sorry.

You can create a logical band maths expression (latitude > 35 and latitude < 40)
This creates a mask band for all pixels which fulfill this criterion. You can then use this mask in the plot view. I haven’t tried it but it should work.

What is a plot view?

I searched but I don’t know.

sorry, I meant the scatter plot view.

Alternatively, you can create a WKT mask of your latitude here: https://arthur-e.github.io/Wicket/sandbox-gmaps3.html

Then import it in SNAP (right-click > geometry from WKT) and then use it as a mask in the scatter plot or correlative plot view.

Is there a usage fee for the site?