## 2 Materials
### Helicopter-Borne Ice Penetrating Radar Survey  
Ice penetration radar (IPR) is one of the most powerful geophysical exploration tools for observing glaciers. The IPR transmits radio waves regularly and records the returning echoes. The resulting standard image consists of the x-axis of each pulse's transmission time (commonly called as along-track) and the y-axis of the time window (64,000 ns in this study) of each record. Because glaciers have a small dielectric absorption in the radio frequency band, radio echoes can be detected from the bottom of the ice sheet with a glacier thickness of 2 km or more. During the Antarctic summer seasons in 2016-2017, a team of Korea Polar Research Institute (KOPRI) organized a helicopter-borne survey over Campbell Glacier. An AS-350 helicopter was equipped with an IPR, Trimble Net-R9 dual-frequency (1 Hz, 2 Hz) Global Navigation Satellite System (GNSS), Novatel SPAN IGM-1A inertial navigation system, and Renishaw ILM-1200 HR laser altimeter (average of 1000 data sample, accuracy of 10 cm, and resolution of 1 cm). The IPR measurement were conducted for a total of 655 km survey  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**One-Day DInSAR Pair** & **Perpendicular BASELINE** & **Height Ambiguity of One** \\ (YYYYMMDD\_YYYYMMDD) & **(m)** & **Fringe (2.7) (m)** \\ \hline
20100616\_20100617 & 31.60 & \(-\)241.56 \\
20100702\_20100703 & \(-\)52.53 & 145.08 \\
20101225\_20101226 & 47.70 & \(-\)160.  
line over Campbell Glacier, especially intensively in the downstream of the glacier that is covered by the SAR dataset. The IPR used for this study is a High Capability Airborne Radar Sounder 2 (HiCARS2) designed by the University of Texas Institute for Geophysics (UTIG), with a center frequency of 60 MHz and 1 \(\upmu\)s wide chirp, linearly sweeping the frequency from 52.7 to 67.5 MHz with a 6250 Hz pulse repetition frequency, and 8 kW peak pulse power to improve propagation [25]. It is a phase coherent radar system with about 2.8 m vertical resolution on ice [26; 27; 28]. All measurements from these pieces of equipment were received, controlled, and recorded in a storage by the Environment for Linked Streams Acquisition (ELSA) system developed by UTIG in 2009 [25; 26]. The IPR used in this study was first carried on a Twin Otter airplane in 2001 to survey the Siple Coast [29] and B15a iceberg [30] in Antarctica. The glacier surface and the glacier/bedrock interface are picked using a semi-automatic method as follows. The altitude of the glacier surface (\(E_{s}\)) is obtained from the GPS-measured altitude (\(E_{G}\)) and the laser altimeter-driven distance of the helicopter from the surface (\(L\)) by:  
\[E_{s}=E_{G}-L. \tag{1}\]  
The altitude of the glacier/bedrock interface (\(E_{b}\)) is obtained from the glacier-bedrock peaking value in the radargram:  
\[E_{b}=E_{s}-Z. \tag{2}\]  
Here, a nominal velocity of glacial ice, 0.17 m/ns, was used to calculate the ice thickness \(Z\)[31; 32]. IPR-derived surface and bed map of the downstream part of the Campbell Glacier were produced by kriging interpolation [33] of the survey profiles. The kriging technique is a regression analysis method used in geostatistics. The basis of kriging is predicting a function value at a given point by calculating the weighted average of the known function values neighborhood that point. The predicted value at position \(p_{0}\) (\(\hat{X}(p_{0})\)) is calculated by:  
\[\hat{X}(p_{0})=\sum_{i=1}^{N}\omega_{i}\;X(p_{i}), \tag{3}\]  
where \(N\) is the number of observations, \(\omega_{i}\) is the weight of observation point \(p_{i}\), and \(X(p_{i})\) is the observation value at position \(p_{i}\). The weight (\(\omega\)) decreases as the distance (\(d_{io}\)) between \(p_{0}\) and \(p_{i}\) in Equation (4). In this study, ordinary kriging is used among kriging methods. Ordinary kriging ensures that the sum of weights (\(\omega\)) to 1 (Equation (5)) so that the estimation is not biased.