Snow wetness retrieved from close-range L-band radiometry in the western Greenland ablation zone

Reza Naderpour,Mike Schwank,Derek Houtz

doi:10.1017/jog.2020.79

Abstract

AbstractClose-range (CR) L-band radiometry and quasi-simultaneous in situ snow characterizations were conducted in May 2019 at the Swiss Camp research site in the ablation zone of the western Greenland ice sheet. Snow liquid-water and its melt/refreeze are retrieved from microwave antenna temperatures measured with the ground-based L-band radiometer ELBARA-III. The emission model (EM) used in the retrieval is a two-layer configuration of the ‘L-Band Specific Microwave Emission Model of Layered Snowpack’. Consistent snow wetness retrievals were achieved from both single- and multi-angle CR observations of L-band antenna temperatures. This suggests that multi-angle observation is not a pre-requisite for snow wetness retrieval. Therefore, in addition to soil moisture and ocean salinity (SMOS) multi-angle measurements, snow wetness can be estimated from spaceborne L-band brightness temperatures measured at a single observation angle, such as from NASA's SMAP satellite. Our results provide partial validation of a recently presented snow wetness retrieval approach based on the same EM and applied over Greenland using multi-angle SMOS brightness temperatures. Agreement between measured CR antenna temperatures and SMOS brightness temperatures is found to be within the 95% confidence intervals of ELBARA-III and SMOS measurement uncertainties. Our measurements confirm the modeled response of antenna temperatures to diurnal variations of snow wetness.

Highlights

Annual snowfall over the Antarctic and Greenland ice sheets holds water equivalent to ∼6.5 mm of mean sea level
In the ELBARA-III (and ELBARA-II (Schwank and others, 2010)), three internal noise sources are implemented: (i) hot source (HS) of noise temperature THchS realized with a noise diode; (ii) active cold source (ACS) of noise temperature TAchCS realized with a low noise amplifier (LNA) and (iii) matched resistive 50 Ω source (RS) of noise temperature TRchS
Responses of single- and multi-angle satellite (SMOS) and CR (ELBARA-III) microwave measurements to temporal variations of snowpack conditions are presented in Sections 5.1.1 and 5.1.2, respectively

Summary

Introduction

Annual snowfall over the Antarctic and Greenland ice sheets holds water equivalent to ∼6.5 mm of mean sea level. Other active (Drewry and others, 1991; Jezek and others, 1993; Long and Drinkwater, 1999; Nghiem and others, 2001; Li and others, 2017) and passive (Jay Zwally and Fiegles, 1994; Abdalati and Steffen, 1995; Steffen and others, 2004; Mote, 2007) microwave remote-sensing techniques exist which employ observations at frequencies higher than L-band (1–2 GHz) to detect liquid water in snow. While these methods provide valuable insight, they are limited to binary detection of dry/wet snow due to the limited penetration depth of higher frequency microwaves in snow (Hofer and Mätzler, 1980; Mätzler and others, 1984). Limited research has been published on the retrieval of snow properties using inversion of microwave emission models (EMs) (Tedesco and others, 2006), yet still these studies employ higher-frequency microwaves, limited by low penetration depth especially into wet snow

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Conclusion