Scientific Project C4 - Hydrological surface
processes during the development of an artificial catchment
Staff
project homepage at WSL
This project aims at an improved understanding of the
influence of orientated surface structures (such as erosion gullies caused
by runoff) on soil moisture measurements using microwave radiometry. To
develop a radiometer-based method for quantifying the gradual formation of
dominant near-surface flow patterns on sandy soils is one of the main goals
of this project.
The naturally emitted microwave radiation of a soil is a function of the
soil’s surface temperature and its emissivity. Since the emissivity
correlates strongly with the soil water content it is possible to determine
soil moisture from microwave measurements. Two radiometers measuring at 1.4
GHz (ELBARA) and 11.4 GHz (MORA), respectively, will be used to measure the
microwave emission of the soil. The soil surface temperature will be
measured separately with an IR-radiometer. Additionally, in-situ
measurements of soil moisture and temperature at different depths will be
carried out using TDR’s and thermocouples.
The signal received at the radiometer is an integrated value originating
from an area of a certain extent (the so-called footprint), the size of
which depends on the distance between the radiometer and the observed scene
and the viewing angle of the radiometer. We will test a de-convolution
algorithm applied to the measured, spatially integrated radiation for its
potential to determine sub-footprint fractions of dominant water containing
surface areas. Furthermore, parameters characterizing the geometry of these
preferential runoff paths will be deduced from the polarization state of the
microwave radiation signals.
In the first project stage different test plot experiments have been carried
out at the Swiss Federal Research Institute WSL in Birmensdorf (Switzerland).
Aim of these experiments was to investigate the influence of different
surface patterns on the microwave signatures under controlled conditions.
First, a rotating wooden frame stringed with parallel wires was placed in
the radiometer footprint and microwave emission was recorded for different
wire distances and wire orientations relative to the plane of incidence.
For the next experiments a 3 m x 4 m tiltable box, filled with material from
the Hühnerwasser catchment, was placed in the footprint. Directional surface
heterogeneities in the form of parallel rills with different dimensions and
orientations were imprinted into the sand surface. In several irrigation
experiments time series of brightness temperatures were measured for
different surface patterns at varying surface moistures.
In the second project stage the radiometers will be installed in the
Hühnerwasser catchment (approximately in the second half of the year 2008)
for a continuous monitoring of the natural development of soil moisture
patterns on a slope in the course of time. The radiometers will be set up on
a 10 m tower at the edge of the investigation area. They can be rotated
horizontally as well as vertically which makes it possible to observe
different slope sections with different slope angles inside and outside (where
we can manipulate the soil surface) of the investigation area. Ground truth
measurements of soil moisture and temperature (TDR, thermocouples) will be
carried out for validation purposes and soil surface topography will be
determined simultaneously from digital photography.
Measurements will be carried out continuously for at least one year. This
enables us to investigate the influence of different seasons with their
specific weather conditions (soil frost events, snow melt, intense rainfalls,
dry spells etc.) on the natural development of the emerging flow paths.
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