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.

中文翻译：

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ApRES 信号削波导致的深度相关伪影

在格陵兰冰川部署了几个自主相敏无线电回波探测仪 (ApRES)，以研究冰的变形。测试了不同的衰减设置，并观察到，在去斜坡的 ApRES 信号存在削波的情况下，每种设置都会产生不同的结果。具体而言，与较低衰减相关的较高水平的削波导致日垂直累积位移随深度的明显线性增加，并模糊了基底反射器在返回幅度中的可见性。一个合成去斜坡信号的例子证实，这些类型的伪影是由削波引入的类方波特征的谐波引入造成的。当近地表内反射器的垂直位置随时间变化时，垂直位移随深度呈明显线性增加。回波幅度中的伪影可能会掩盖来自内部反射器和基底反射器的回波，从而难以检测冰的厚度演变和正确估计垂直速度。ApRES 部署期间表面熔化的变化可以在短时间内大大调制接收到的信号强度，因此我们建议在此类位置部署时使用更高的衰减器设置。