I am a masters student, and trying to calculate the volume change for a glacier. I have 4 different DEMs, none of them are of the bedrock topography below the glacier. I have read that you can simply find the volume change by subtracting DEMs (older-newer) and then multiply by cell size to get the volume change. But the numbers I am getting does not give much sense to me at this moment, it basically tells me that the glacier is gaining volume, rather than losing it.
Anyone have any experience doing this type of analysis?