What does the output value of a band exactly mean?

Apps / Services Python SDK
1

Hi,
My answer is probably very similar to the source: What does the band's value signify of Landsat-8 L1C, Sentinel-2 L1C and MODIS MCD43A4
But how do I know, if I get a band output (I use Sentinel 2 2A), that the value is high or low? Is there some kind of source that tells me if the output is high or low ? The source: https://docs.sentinel-hub.com/api/latest/data/sentinel-2-l2a/#available-bands-and-data does tell me about the details of each band, but not at which range the data could and should be and when a value should be high or low. I’m looking for ages for a good source but I can’t find one. Any advice or source is welcome.

2

Dear @rubenski0345 ,

High and Low are quite subjective terms to quantify physical values.

The data provided by Sentinel-2 sensors are expressed in Reflectance which generally ranges from 0 to 1. A reflectance of 0 in an image means that all the incoming solar radiation is absorbed by the surface, whereas a value of 1 indicates that all the incoming solar radiation is reflected back towards space. For more information, I would suggest looking at Humboldt State University’s introduction course.

For Sentinel-2 L1C the reflectance measured includes the signal from the atmosphere, whereas for Sentinel-2 L2A the images are corrected using a model to remove the effect of the atmosphere in order to obtain information about the solar energy reflected by the surface only. In Sentinel Hub, you can access either Reflectance (generally between 0 and 1) or DN, which is simply REFLECTANCE * 10000 for numerical reasons. There is an indication of the typical range in our data description page for Sentinel-2 L2A. This being said, a “high” or “low” value will depend on the surface you are studying.

I hope this answers your question.

Maxim

3

Hi Maxim,
aha, I understand now that reflectance can’t be high or low. Though is there a unit used for the reflectance/DN? Then I can easier calculate or convert with it. Or is it, because it’s between 0 and 1, a percentage amount of reflectance?

ps thanks for answering quickly