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Discrepancy between altimetry and GPS data?  

Hello fellow educators!

I recently used 'Unit 4: An uplifting story of sea level change" during a high school Oceanography course. The students and I noticed that there appears to be a disagreement in the altimetry and GPS data from Helheim Glacier during the period 2006-2009. During that timeframe, laser altimetry data shows that the ice elevation of Helheim glacier is increasing, so we would expect the bedrock GPS data to show that bedrock elevation decreased during that period. However, the bedrock GPS data shows that the bedrock elevation in rising during that time period.

What explains this discrepancy? We are stumped!


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Thank you for this insightful observation. I have forwarded your message to someone who might be able to help answer your question. -Beth


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Awesome, thanks Beth! - Shelby


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Here is from Leigh Stearns, one of the module authors "Hmm. Good question. I think the 'discrepancy' is due to the fact that the repeat altimetry is at a kind of odd place on the glacier (where the two tributaries meet), so it isn't necessarily capturing what the whole (integrated) trunk is doing. In other words, the altimetry is assessing change at a discrete point, while the GPS is "weighing" a much larger area."


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Neat! Makes sense to me. The students will be stoked to hear this possible explanation!


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