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Abstract
With the development of spaceborne global navigation satellite system-reflectometry (GNSS-R), it can be used for terrestrial applications as a promising remote sensing tool, such as soil moisture (SM) retrieval. The reflected L-band GNSS signal from the land surface can simultaneously generate coherent and incoherent scattering, depending on surface roughness. However, the contribution of the incoherent component was directly ignored in previous GNSS-R land soil moisture content retrieval due to the hypothesis of its relatively small proportion. In this paper, a detection method is proposed to distinguish the coherence of land GNSS-R delay-Doppler map (DDM) from the cyclone global navigation satellite system (CYGNSS) mission in terms of DDM power-spreading features, which are characterized by different classification estimators. The results show that the trailing edge slope of normalized integrated time-delay waveform presents a better performance to recognize coherent and incoherent dominated observations, indicating that 89.6% of CYGNSS land observations are dominated by the coherent component. Furthermore, the impact of the land GNSS-Reflected DDM coherence on soil moisture retrieval is evaluated from 19-month CYGNSS data. The experiment results show that the influence of incoherent component and incoherent observations is marginal for CYGNSS soil moisture retrieval, and the RMSE of GNSS-R derived soil moisture reaches 0.04 cm3/cm3.
Highlights
IntroductionSince the L-band microwave has a strong sensitivity to the change of surface Soil moisture (SM) and can more penetrate the atmosphere and vegetation canopy, it has been widely used as the main soil moisture remote sensing frequency band in the satellite-based radiometer and radar missions [1]
Soil moisture (SM) is an essential parameter for the hydrology and energy cycle
The experiment results show that the influence of incoherent component and incoherent observations is marginal for cyclone global navigation satellite system (CYGNSS) soil moisture retrieval, and the root-mean-square error (RMSE) of global navigation satellite system-reflectometry (GNSS-R) derived soil moisture reaches 0.04 cm3 /cm3
Summary
Since the L-band microwave has a strong sensitivity to the change of surface SM and can more penetrate the atmosphere and vegetation canopy, it has been widely used as the main soil moisture remote sensing frequency band in the satellite-based radiometer and radar missions [1]. Such as the European Space Agency’s (ESA) Soil Moisture and Ocean. The observe system directly receives the pre-existing signals transmitted by the GNSS satellites reflected off the Earth’s surface [3], and the received scattering signals are typically expressed in a delay-Doppler map (DDM) for Earth’s surface geophysical parameters retrieval [4], which provide a new paradigm in the land remote sensing to cover the space-time gap of the traditional high-cost dedicated monostatic active or passive satellite missions
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