The state of a geophysical parameter can be retrieved by converting information that is contained...
Geophysical Parameter: e.g. soil moisture
Observable Quantity: radiance measured by the antenna
The TU Wien method represents an inverse model.
Models what we would observe (measure) under certain geophysical conditions
Processes involved in the propagation of the radiation from the Earth’s surface to the antenna:
interactions of the waves with illuminated matter such as soil, vegetation canopy or atmospheric particles
$$Y = f(x, \Omega)$$
$Y$...observable quantities (i.e., radiance measured by the antenna)
$x$...geophysical parameters of interest (e.g., temperature or soil moisture)
$\Omega$...set of controllable measurement conditions (e.g., the wavelengths, viewing direction, time, sun position, polarization, ...)
$f(.)$...complex function that relates x to Y (i.e., the formulation of the wave propagation and interaction processes)
Inversion of the forward model ⇒ retrieval of the parameters of interest from the observables.
We observe certain parameter values (e.g. backscatter) - what are the geophysical conditions that we are actually
interested in (e.g. soil moisture)?
$$\hat{x} = g(\hat{Y}, \hat{\Omega})$$
$\hat{x}$ ...estimates of the geophysical parameters obtained by g(.)
$g(.)$ ...complex function
$\hat{Y}$ ...actual measurements
$\hat{\Omega}$ ...approximations of the measurement conditions
developed at the Vienna University of Technology
physically motivated empirical change detection method
no iterative adjustment process needed - direct retrieval from backscatter measurements possible
model parameters calibration requires a multi-year radar backscatter archive ⇒ land cover, surface roughness...
Variations of the backscatter coefficient $\sigma^0$ are related to...
Datatsets: European C-Band Scatterometers ESCAT and ASCAT (multi-incidence angle and multi-beam viewing capability)
Vegetation correction
Soil moisture estimation
Soil moisture uncertainty estimation
...each of these steps is described in a respective lecture!