Depth-dependent artifacts resulting from ApRES signal clipping

Abstract Several autonomous phase-sensitive radio-echo sounders (ApRES) were deployed at Greenland glaciers to investigate ice deformation. Different attenuation settings were tested and it was observed that, in the presence of clipping of the deramped ApRES signal, each setting produced a different...

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Bibliographic Details
Published in:Annals of Glaciology
Main Authors: Vaňková, Irena, Nicholls, Keith W., Xie, Surui, Parizek, Byron R., Voytenko, Denis, Holland, David M.
Format: Article in Journal/Newspaper
Language:English
Published: Cambridge University Press (CUP) 2020
Subjects:
Online Access:http://dx.doi.org/10.1017/aog.2020.56
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0260305520000567
Description
Summary:Abstract Several autonomous phase-sensitive radio-echo sounders (ApRES) were deployed at Greenland glaciers to investigate ice deformation. Different attenuation settings were tested and it was observed that, in the presence of clipping of the deramped ApRES signal, each setting produced a different result. Specifically, higher levels of clipping associated with lower attenuation produced an apparent linear increase of diurnal vertical cumulative displacement with depth, and obscured the visibility of the basal reflector in the return amplitude. An example with a synthetic deramped signal confirmed that these types of artifacts result from the introduction of harmonics from square-wave-like features introduced by clipping. Apparent linear increase of vertical displacement with depth occurs when the vertical position of a near-surface internal reflector changes in time. Artifacts in the return amplitude may obscure returns from internal reflectors and the basal reflector, making it difficult to detect thickness evolution of the ice and to correctly estimate vertical velocities. Variations in surface melt during ApRES deployments can substantially modulate the received signal strength on short timescales, and we therefore recommend using higher attenuator settings for deployments in such locations.