Characteristics and limitations of GPS L1 observations from submerged antennas

Abstract

Observations from a submerged GNSS antenna underneath a snowpack need to be analyzed to investigate its potential for snowpack characterization. The magnitude of the main interaction processes involved in the GPS L1 signal propagation through different layers of snow, ice, or freshwater is examined theoretically in the present paper. For this purpose, the GPS signal penetration depth, attenuation, reflection, refraction as well as the excess path length are theoretically investigated. Liquid water exerts the largest influence on GPS signal propagation through a snowpack. An experiment is thus set up with a submerged geodetic GPS antenna to investigate the influence of liquid water on the GPS observations. The experimental results correspond well with theory and show that the GPS signal penetrates the liquid water up to three centimeters. The error in the height component due to the signal propagation delay in water can be corrected with a newly derived model. The water level above the submerged antenna could also be estimated.

Retrieval of Snow Water Equivalent, Liquid Water Content, and Snow Height of Dry and Wet Snow by Combining GPS Signal Attenuation and Time Delay

“…In particular, as soon as liquid water is present, the change in signal propagation in snow is pronounced. The main effects are summarized in the following: for more details on the calculation of GPS signal attenuation, reflection, and refraction as well as signal power losses related to snow, we refer the reader to Koch et al () and Steiner, Meindl, and Geiger ().…”

“…The incident, reflected, and transmitted signals follow the Fresnel equations of reflection and transmission and the law of conservation of power (Woodhouse, ). The mean reflected power P r consists of a real and an imaginary part of the complex circular reflection coefficients with co‐ and cross‐polarized components (Steiner, Meindl, & Geiger, ). These components are used to describe the linear horizontal and vertical reflection coefficients, r h and r v , which are related to the complex permittivity of snow as well as the incident and refracted angles in snow.…”

“…These components are used to describe the linear horizontal and vertical reflection coefficients, r h and r v , which are related to the complex permittivity of snow as well as the incident and refracted angles in snow. The detailed calculation of the reflection angles, coefficients, and the reflected power is described in Koch et al () and Steiner, Meindl, and Geiger (). Hence, the reflected power P r is given by …”

“…Koch et al () used GPS signal strength attenuation of buried antennas to continuously and nondestructively derive LWC. Steiner et al () theoretically and practically investigated the behavior of GPS signals of submerged antennas. By exploiting the GNSS carrier phases using low‐cost sensors, Henkel et al () derived SWE for dry‐snow conditions.…”

An assessment of sub snow GPS for quantification of snow water equivalent

“…For that reason, an assumption is made: The GPS path delay in the layered snowpack is 20 assumed to be nearly independent on snow density and the distribution of liquid water. Water has the highest impact on GPS observations within a snowpack (Steiner et al, 2018). Neglecting snow density and the water distribution, the model simplifies to a single water layer ( Fig.…”