First please take a look at this whole thread, the Creation DEM from S-1 is discussed there,
In general it’s possible to get an idea not mathematical results about the coherence of the study area, in case the study area has less stable objects within the resolution of the SAR images two passes, and highly vegetated or smooth area in this case and expectation of low coherence is first prediction; vise versa, spread of stable objects such as buildings ,… could give an expectation of high coherent images.
But it’s not possible to get a mathematical estimation of the coherence without processing the pair.
It is possible to calculate the Radar Vegetation Index, RVI, this topic is quite discussed in here, and how could be modified the equation,
Also you could take a look at
Agricultural Applications with SAR Data
Also it is possible to classify S-1 images (GRD)
LAND COVER MAPPING USING SENTINEL-1 SAR DATA
DEFORESTATION MONITORING WITH SENTINEL-1 Case Study: Paraguay, 2018