Exploring Signal of Opportunity from GNSS for Snow Remote Sensing

Abstract:

Exploring signal of opportunity from the global navigational satellite system (GNSS) for geophysical remote sensing has drawn increasing interest. The recent launch of the cyclone global navigational satellite system (CYGNSS) and the widely available GNSS reflectivity and delay-Doppler map (DDM) data in low latitudes is followed by intense research on ocean wind speed and soil moisture remote sensing. The concept of signal of opportunity has also been extended to P-band and been demonstrated in a ground based setting for snow water equivalent (SWE) retrieval by exploring the phase difference between the ground reflected signal and the direct signal from GNSS satellites. Such phase based approach is robust to complex snow stratigraphy and grain size inhomogeneity, and is thus promising.

In this paper, we aim to promote the development of GNSS signal of opportunity techniques for cryosphere observation. In particular, we focus on the remote sensing of terrestrial snow and snow on sea ice using GNSS signals. Our research are three-folds: (i) We explore the possibility of deriving coherent phase from satellite based GNSS-reflection (GNSS-R) observations, and link the coherent phase change to SWE changes. For terrestrial snow in forest, effects of forest scattering on the coherent phase change are also examined. (ii) We develop models to simulate DDM for snow covered regions and explore the signatures of DDM that varies with snow accumulation. (iii) We examine the possibility of formulating interferometric DDM and the potential to derive effective height information of the reflecting interface of high spatial resolution by combing GNSS-R observations from multiple GNSS satellites. Such effective height includes information about snow accumulation and has potential in various geophysical observations.

Key words: cryosphere; snow; signal of opportunity; GNSS-R; coherent phase; delay Doppler map; interferometric DDM