There's a wide number of possible applications for surface soil moisture.
You will be introduced to three of them:
infiltration: dependent on a large number of parameters (soil texture and structure, vegetation coverage, soil temperature, present water content...)
those parameters are not known on a global scale
⇒ empirical method for estimating root zone soil moisture from surface soil moisture measurements (Wagner et al. 1999)
Water balance equation for the reservoir:
$\Theta(t)\;=\;\frac{1}{T}\int_{-\infty}^t \! \Theta_S(\tau)\;*\;e^{(-\frac{t-\tau}{T})} \, \mathrm{d}\tau$, $with\;T=\frac{L}{C}$Θ...volumetric water content of the reservoir
ΘS...water content of the surface layer
t...time
L...depth of the reservoir layer
C...pseudo diffusivity coefficient incorporating all soil properties
T...characteristic time length (increases with L and decreases with C)
Discrete formulation, defined as soil water index (SWI):
$SWI(t)\;=\;\frac{\sum_i{sm(t)\;*\;e^{(-\frac{t-t_i}{T})}}}{\sum_i{e^{(-\frac{t-t_i}{T})}}}$, $for\;t_i\;\le\;t$In 2010, surface soil moisture was recognised as an Essential Climate Variable (ECV)
Important dataset for IPCC (Intergovernmental Panel on Climate Change) and UNFCCC (United Nations Framework Convention on Climate Change)
ECV data records should be as long, complete and consistent as possible
make use of multiple data sources, including active and passive microwave observations (from ESCAT, ASCAT, SMMR, SSM/I, TMI, AMSR-E, Windsat, AMSR2)
It was found that the merging process improved the spatial and temporal coverage while minimally impacting the accuracy of the soil moisture retrievals (Liu et al., 2012).
Important steps in the fusion process:
This approach allows combining surface soil moisture data derived from different instruments with substantially different
instrument characteristics.
Moreover, it's straight forward to further enrich the ECV dataset with Level 2 data from other sensors (e.g. SMOS, SMAP...).
Correction/improvement of first guess rainfall estimates
Estimating rainfall
- a first analysis of this approach (SM2RAIN) shows promising results
... from ASCAT surface soil moisture retrieval based on SM2RAIN: