I would like to understand to view the health of a glacier using optical or SAR data. What season would be the best for observation? Is the ablation season better or the accumulation season? More specifically I am targeting the southern slope of the Himalayan belt in India/Nepal.
Looking around at some random articles, for example Karpilo 2009, Geissler et al 2021, Litt et al. 2019, and Racoviteanu et al 2008 my impression is that researchers primarily use images of the glacier taken near the end of the ablation season. (Apart from anything else, I imagine it's just the best time to see the edges and the details of the glacier.)
The last paper in that list (Racoviteanu et al 2008) says they acquired data both at the end of the accumulation season and the ablation season. But they also say this:
Scenes acquired at the end of the ablation season are useful to identify the end-of-summer snowline altitude (SLA), considered to be directly related to variations in a glacier's mass balance
This page adds:
The snowline at the end of the summer season is often used to demarcate the equilibrium line on satellite images of glaciers.