Abstract
AbstractThe thickness of glaciers in High-Mountain Asia (HMA) is critical in determining when the ice reserve will be lost as these glaciers thin but is remarkably poorly known because very few measurements have been made. Through a series of ground-based and airborne field tests, we have adapted a low-frequency ice-penetrating radar developed originally for Antarctic over-snow surveys, for deployment as a helicopter-borne system to increase the number of measurements. The manoeuvrability provided by helicopters and the ability of our system to detect glacier beds through thick, dirty, temperate ice makes it well suited to increase greatly the sample of measurements available for calibrating ice thickness models on the regional and global scale. The Bedmap Himalayas radar-survey system can reduce the uncertainty in present-day ice volumes and therefore in projections of when HMA's river catchments will lose this hydrological buffer against drought.
Highlights
The manoeuvrability provided by helicopters and the ability of our system to detect glacier beds through thick, dirty, temperate ice makes it well suited to increase greatly the sample of measurements available for calibrating ice thickness models on the regional and global scale
There are ∼90 000 glaciers in High-Mountain Asia (HMA) (Randolph Glacier Inventory Consortium, 2017) but very few have been surveyed for ice thickness
Fixed-wing aircraft have been used to tow low-frequency (1–2.5 MHz) dipole radars to sound through up to 1250 m of temperate ice in Alaska and Patagonia (Conway and others, 2009; Zamora and others, 2009; Rignot and others, 2013), but the reduced manoeuvrability of such aircraft at high altitude makes them unsuited to surveys in HMA, where high mountain walls surround narrow glacier tongues lying largely above 4000 m altitude
Summary
There are ∼90 000 glaciers in High-Mountain Asia (HMA) (Randolph Glacier Inventory Consortium, 2017) but very few have been surveyed for ice thickness. Fixed-wing aircraft have been used to tow low-frequency (1–2.5 MHz) dipole radars to sound through up to 1250 m of temperate ice in Alaska and Patagonia (Conway and others, 2009; Zamora and others, 2009; Rignot and others, 2013), but the reduced manoeuvrability of such aircraft at high altitude makes them unsuited to surveys in HMA, where high mountain walls surround narrow glacier tongues lying largely above 4000 m altitude. There is evidence that antenna orientation parallel to ice flow yields a somewhat stronger bed signal in 25 MHz data in a low-clutter environment over largely debris-free ice (Langhammer and others, 2019b). (iii) How large are the clutter signals relative to the bed signal, and how do they vary with frequency and survey pattern?
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