Télédétection et ressources en eau/Remote sensing and water resources
21
All these approaches put the accent on the uses of remote sensing as a tool for the
segmentation of space and emphasize the uses of this segmentation of space as the initial phase
for the modelling which is made possible by remote sensing, GIS and DEM.
Mapping of parameters that vary over time (water balance)
Remote sensing is also presented as a tool for mapping parameters that vary over time
(temperature, humidity) and that are difficult to obtain from the standard network of point
measurements. This aspect is particularly interesting as it poses the problem of changing the
approach from point measurements to base surface information.
Two written presentations (Hurtado Santi et al., Chebouni et al.) start from thermal infrared
maps and demonstrate the use of theoretical models in the exchange balance to approach the
actual evapotranspiration (ET) by using the differential between radiative and aerodynamic
temperatures. The applications were carried out in semi-arid regions of Arizona, the Sahel and
central Spain. Remote sensing is herein described as a tool for managing spatial information, in
this case the objective being the production of ET maps at a regional level.
Finally, one presentation (Gineste) covers the contribution of ERS radar data to the
estimation of soil humidity in a small watershed in France. The results are insufficient to produce
soil humidity maps as the calibration of the images is still a major problem. One the other hand,
they can provide a relative vision of the dynamics and of the spatial distribution of humidity on
the watershed. The main interest of this approach resides, therefore, in a visualization of temporal
and spatial variations of surface moisture defined by hydrological models. These results can be
used to validate the models themselves.
Objective segmentation of space - reference to the concept of hydrologically homogenous areas
Streamflow modelling or simply understanding of the hydrological environment systematically
refers to the utilization of spatial data as a tool for segmenting land into homogenous areas. Even
if often this tool is not defined as such, it is nevertheless present in most of the presentations.
Remote sensing and GIS appear to be the main tool for segmenting space. Practically all the
presentations that refer to land use include this segmentation phase. Some only present the
segmentation phase and the cartographic results without proceeding to the modelling phase,
which is the main link to the environmental mechanisms that are being studied.
Other presentations propose a reflection on the choice and the meaning of homogenous
areas: these areas, homogeneous on the images (according to visual aspects), should also
correspond to similar functionality according to the theme which is being studied. It is possible to
verify (Viné), that visual homogeneity does not guarantee homogenous behaviour.
Segmented data can then be included in a modelling process that is usually the final
objective: segmentation of space is usually only the initial step of modelling applications.
Hydrological modelling phase
In a spatial approach to streamflow modelling, there is an evident separation into two phases:
first the segmentation of space and then the modelling itself. Apart from the implementation of
these two key phases, a number of presentations have dwelled on their implementation, including
research and methodological aspects. Segmentation of space and distributed modelling have in
21
All these approaches put the accent on the uses of remote sensing as a tool for the
segmentation of space and emphasize the uses of this segmentation of space as the initial phase
for the modelling which is made possible by remote sensing, GIS and DEM.
Mapping of parameters that vary over time (water balance)
Remote sensing is also presented as a tool for mapping parameters that vary over time
(temperature, humidity) and that are difficult to obtain from the standard network of point
measurements. This aspect is particularly interesting as it poses the problem of changing the
approach from point measurements to base surface information.
Two written presentations (Hurtado Santi et al., Chebouni et al.) start from thermal infrared
maps and demonstrate the use of theoretical models in the exchange balance to approach the
actual evapotranspiration (ET) by using the differential between radiative and aerodynamic
temperatures. The applications were carried out in semi-arid regions of Arizona, the Sahel and
central Spain. Remote sensing is herein described as a tool for managing spatial information, in
this case the objective being the production of ET maps at a regional level.
Finally, one presentation (Gineste) covers the contribution of ERS radar data to the
estimation of soil humidity in a small watershed in France. The results are insufficient to produce
soil humidity maps as the calibration of the images is still a major problem. One the other hand,
they can provide a relative vision of the dynamics and of the spatial distribution of humidity on
the watershed. The main interest of this approach resides, therefore, in a visualization of temporal
and spatial variations of surface moisture defined by hydrological models. These results can be
used to validate the models themselves.
Objective segmentation of space - reference to the concept of hydrologically homogenous areas
Streamflow modelling or simply understanding of the hydrological environment systematically
refers to the utilization of spatial data as a tool for segmenting land into homogenous areas. Even
if often this tool is not defined as such, it is nevertheless present in most of the presentations.
Remote sensing and GIS appear to be the main tool for segmenting space. Practically all the
presentations that refer to land use include this segmentation phase. Some only present the
segmentation phase and the cartographic results without proceeding to the modelling phase,
which is the main link to the environmental mechanisms that are being studied.
Other presentations propose a reflection on the choice and the meaning of homogenous
areas: these areas, homogeneous on the images (according to visual aspects), should also
correspond to similar functionality according to the theme which is being studied. It is possible to
verify (Viné), that visual homogeneity does not guarantee homogenous behaviour.
Segmented data can then be included in a modelling process that is usually the final
objective: segmentation of space is usually only the initial step of modelling applications.
Hydrological modelling phase
In a spatial approach to streamflow modelling, there is an evident separation into two phases:
first the segmentation of space and then the modelling itself. Apart from the implementation of
these two key phases, a number of presentations have dwelled on their implementation, including
research and methodological aspects. Segmentation of space and distributed modelling have in