# Giant Cavern the Size of Manhattan Under Thwaites Glacier in West Antarctica - how was satellite and airborne radar data combined?

This is a follow-up question to Giant Cavern the Size of Manhattan Under Thwaites Glacier in West Antarctica.

The work is reported in an open access paper in Science: Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica which is very technical, thorough, and hard for me to understand.

The work is based on a substantial amount of radar data, both SAR (Synthetic Aperture Radar) from several satellites, and (from Pasadena Now) ...by ice-penetrating radar in NASA’s Operation IceBridge, an airborne campaign that began in 2010 and studies connections between the polar regions and the global climate.

Is it possible to explain the differences between the two kinds of radar data (space and airborne) and how they were combined and used together to establish the size/volume and growth of this unexpectedly large amount of liquid water below the glacier?

• I guessed correctly did I not ? :) – gansub Feb 4 at 2:24
• @gansub "I guess that you are thinking just now of what a duck on top of a piano would look like." I guessed correctly as well, did I not? – uhoh Feb 4 at 2:27
• No I meant your next question here. You are the first to bring the latest scientific findings to this site and ask deep penetrating questions. I was referring to that. – gansub Feb 4 at 2:29
• yep, I mean that you first planted the idea in my head here and that caused me to ask this, so it's not a prediction, it's self-fulfilling prophecy. – uhoh Feb 4 at 2:43
• @gansub well I'm not sure I'm such a big effect, but I do enjoy asking questions. I was originally recommended to this site here and I think it's a great site with lots of potential as awareness of this planet (and others) increases. I don't think beta is something to be avoided necessarily. Anyway thanks and I'll keep asking! – uhoh Feb 4 at 3:11

The paper basically combines multiple datasets to figure out the changes in ice surface elevation and ice thickness at tidal and multi-year timescales. That way they were able to study grounding line migration, and the melt rate of the glacier and its corresponding ice shelf from above and below. Then they were able to make inferences of the processes producing glacier melting, specially basal melting that is difficult to measure directly.

They actually used three datasets:

1. DInSAR: Standing for Differential Interferometric Synthetic Aperture Radar. It is basically a technique that compares the phase of two SAR images acquired at different time to compute uplift/subsidence of the surface with great accuracy (usually millimeters). So they were able to see the surface of the ice shelf rise and lower with the tides, and also compute surface flow velocities.

2. IceBridge MCoRDS: Airborne radar depth sounder MCoRDS (Multichannel Coherent Radar Depth Sounder) operated by NASA mission IceBridge. This is a much more powerful radar operated close to the surface and designed to penetrate the ice, allowing to see the bedrock topography beneath the ice and some of the structure above the bedrock, such as water/ice transitions or layers of ice with distinct dielectric properties. This allowed them to know the ice thickness and bedrock topography.

3. TDX DEM: TanDEM-X Digital Elevation Model. This are Surface topography models generated using single pass InSAR data provided by two SAR satellites that orbit in tandem formation (one immediately behind the other). This allows precise surface topography measurements, that are also needed for the DInSAR processing.

I hope that helps. It is a very interesting work. Although the "giant cavern" part is not the most relevant part of it at all, but it was great for catchy headlines.

• +1 This is exactly what I needed to read, thank you! – uhoh Feb 4 at 6:04