Methodology:

For each site, a suite of four quadrature (quad-) polarimetric measurements were collected using an autonomous phase-sensitive radio echo sounder (ApRES) in a single-input single-output configuration. Each measurement consisted of 100 chirps, with each chirp consisting of a linear sweep from 200 to 400 MHz over the course of 1 second, corresponding to a centre frequency of 300 MHz over a bandwidth of 200 MHz. For each measurement, two open-structure antennas (1 transmitting, 1 receiving) were positioned with their centres 8.00 m apart in combinations of four orthogonal antenna orientations, where antennas were positioned in either a horizontal (h) or vertical (v) alignment with respect to the antenna's electric plane. The four orientation combinations are therefore hh, hv, vv, and vh. Measurements were conducted sequentially, and each antenna pair orientation was established by rotating one or both antennas by 90° with respect to their previous orientations while keeping the position of each antenna centre constant. The antenna plane (parallel to the h orientation; 110°) was oriented perpendicular to the transect line (20°). The complete data collection period at each site, from the start of setup to the conclusion of packing, was ~30 minutes.

Data collection:

Data collection: SISO autonomous phase-sensitive radio-echo sounder (version dated to 20170925) with 2x open-structure ("skeleton-slot") antennas.

Data analysis and processing: MATLAB.

Data quality:

The coarse-range (amplitude-derived) vertical (depth) resolution of the ApRES is 0.54 m. The azimuthal accuracy is unknown and is mainly the result of human error in alignment of antennas. A nominal azimuthal error of ±8° is assigned. The data included in this dataset are raw data and are entirely unprocessed.