I am a little confused with the processing levels of Sentinel-1 data. The data downloaded from the ESA website which haven’t gone through the preprocessing workflow is Level 1 data as far as I know but what is the level of the same image after going through the preprocessing workflow? Is it Level 2 now?
Can you please give example and mention the IDs of the data you downloaded?
That’s a real question about terminology.
The definition of processing levels (1 / 2 / 3 / …) and their sub processing flavor depends a bit on each space agency and mission.
There is a kind of generic definition from CEOS and from NASA EOSDIS, both being not fully aligned.
You can read this for instance.
So, this depends on your type of preprocessing.
As long as you stay in sensor unit, it is probably still a level 1 product, even if reprojected.
As you can see from the link above the author is using his own definition as well.
I am personally using another one, considering that the L2 are explicitly geophysical measurements, not in sensor unit, and defining sub processing level for Level 1 (1A = SLC, 1B = GRD, 1C = geocoded, 1D = orthorectified).
So I am afraid there is no definitive answer to your question.
The processing levels do not follow a common specification, as @ghajduch said.
There is just some overlap in the definitions.
Here is the NASA definition: Data Processing Levels | Earthdata (nasa.gov)
For ESA I haven’t found an equivalent.
But for Sentinel-1 it is here: User Guides - Sentinel-1 SAR - Product Types and Processing Levels - Sentinel Online - Sentinel Online
For Sentinel-2 here: User Guides - Sentinel-2 MSI - Processing Levels - Sentinel Online - Sentinel Online (esa.int)