Measuring snow water equivalent from common-offset GPR records through migration velocity analysis

James St Clair,W Steven Holbrook

doi:10.5194/tc-11-2997-2017

Abstract

Abstract. Many mountainous regions depend on seasonal snowfall for their water resources. Current methods of predicting the availability of water resources rely on long-term relationships between stream discharge and snowpack monitoring at isolated locations, which are less reliable during abnormal snow years. Ground-penetrating radar (GPR) has been shown to be an effective tool for measuring snow water equivalent (SWE) because of the close relationship between snow density and radar velocity. However, the standard methods of measuring radar velocity can be time-consuming. Here we apply a migration focusing method originally developed for extracting velocity information from diffracted energy observed in zero-offset seismic sections to the problem of estimating radar velocities in seasonal snow from common-offset GPR data. Diffractions are isolated by plane-wave-destruction (PWD) filtering and the optimal migration velocity is chosen based on the varimax norm of the migrated image. We then use the radar velocity to estimate snow density, depth, and SWE. The GPR-derived SWE estimates are within 6 % of manual SWE measurements when the GPR antenna is coupled to the snow surface and 3–21 % of the manual measurements when the antenna is mounted on the front of a snowmobile ∼ 0.5 m above the snow surface.

Highlights

Many regions of the world are critically dependent on seasonal snowfall for their water resources; accurate estimates of how much water is stored in mountain landscapes are necessary to manage this resource
Comparing the V curves for synthetic diffractions as well as those from our data, we find that V values that are greater than 95 % of the peak value correspond to migrated images that are indistinguishable to the human eye (Fig. 2)
The primary purpose of this study is to develop an efficient processing flow for measuring groundpenetrating radar (GPR) velocity and snow density snow water equivalent (SWE) from common-offset data that requires a minimum amount of human interpretation

Summary

Introduction

Many regions of the world are critically dependent on seasonal snowfall for their water resources; accurate estimates of how much water is stored in mountain landscapes are necessary to manage this resource. In the United States, a large network of SNOTEL sites provides continuous information about snow depth, density, and snow water equivalent (SWE) that is used to make water availability predictions (Serreze et al, 1999). While these sites provide valuable information at a site, scaling these point measurements up for basin- or grid-scale estimates can be challenging (Molotch and Bales, 2005). These data are used to develop empirical relationships between SWE and nearby stream discharge. SWE can be calculated as the product of snow density and snow height

Objectives

Methods

Findings

Conclusion