Analysis of active-passive complementarity and its dependence on vegetation and surface roughness from SMAP observations
Abstract
The Soil Moisture Active Passive (SMAP) mission, which is specially designed for providing high-resolution and frequent-revisit global maps of soil moisture and landscape freeze/thaw state, was launched on 31 January 2015. It is the newest soil moisture dedicated satellite in orbit and is also the first satellite that incorporates an L-band (1.26 GHz) active radar and an L-band (1.41 GHz) passive radiometer. The science data released to the public now includes over two months of coincident active and passive measurements, which provides us an invaluable opportunity to fully explore the complementarity of active and passive observations, especially under a wide range of vegetation and roughness conditions. The objective of this study is to investigate the potential and limitations of the integration of active and passive observations and its dependence on vegetation and surface roughness. To achieve this purpose, we examine the relationship between the surface reflectivity (Rp) calculated from the passive radiometer observations and the backscattering coefficient (σpp) obtained from the active radar. Two defined indexes including the radar vegetation index (RVI) and radar roughness index (RRI) were used to evaluate the effects of the vegetation and roughness on the active-passive complementarity. It is found that both the SMAP radar and radiometer observations show reasonable global spatial pattern. In the sparsely vegetated areas (RVI<0.5) at a global scale, the relationship between the Rp and σpp is exponential, which is consistent with the numerical results obtained from NMM3D. However, for densely vegetated areas, the relationship becomes weak which can be explained by the fact that the signals scattered or emitted from soils are masked by the vegetation, resulting in reduced sensitivity of backscattering coefficients and brightness temperature to soil moisture. It is also found that the surface roughness does not exert obvious effects on the complementary sensitivity of active and passive observations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H31G1484Z
- Keywords:
-
- 1833 Hydroclimatology;
- HYDROLOGYDE: 1843 Land/atmosphere interactions;
- HYDROLOGYDE: 1855 Remote sensing;
- HYDROLOGYDE: 1866 Soil moisture;
- HYDROLOGY