180
M. Menenti
led Menenti (1984) to new insights in the hydrology of groundwater reservoirs in
the Sahara, confinned by follow up investigations in the Western Desert of Egypt
(Bastiaanssen and Menenti, 1990). The SEBAL algorithm described by Bastiaanssen (1995) was applied to assess irrigation perfonnance in the Nile Delta by Bastiaanssen et al. (1992). Seguin et al. (1991) applied the linear relationship approach to produce an indicator of drought conditions in agricultural areas in
France over a three years period.
Examples and additional references on applications are given in Chap. 17.
8.8 Current and Future Observations
The techniques and applications reviewed in the previous chapter span a period of
time during which there has been a significant evolution in sensor technology.
Changes in the type of measurements obtained with earth observation satellites
have been limited. A major technological evolution of airborne sensors has taken
place however. The driving force of such evolution has been the development of
the new International Earth Observing System (IEOS), a very diverse suite of instruments developed by space agencies: NASA, ESA, NASDA and CNES. In
many cases a series of forerunners of the sensors scheduled for flight in the time
frame 1999 - 2005 has been developed to test new technological solutions. The
extent and direction of technological evolution can be documented by looking at
three categories: current satellite sensors, current airborne sensors and future satellite sensors. For accurate and detailed infonnation on missions and satellites for
earth observation the reader is referred to Kramer (1994). See also appendices to
Chap. 20.
Remote sensing studies ofland evaporation have been hampered by the lack of:
simultaneous and accurate measurements of surface albedo and temperature at
spatial resolutions consistent with the spatial variability of terrestrial landscapes;
measurements of the geometry of canopies to detennine surface roughness and
aerodynamic resistances;
measurements ofPBL conditions.
The near future bears promises of significant improvements on all three aspects:
The ASTER sensor system on-board Terra-l (NASA EOS AM-I) will provide sufficient spectral sampling in the VNIR (Visible - Near Infrared) region
to detennine albedo, while the multi-spectral TIR measurements will provide
for the first time a real opportunity for simultaneous detennination of surface
temperature and emissivity.
The Vegetation Canopy Lidar (NASAl ESSP/ VCL) will for the first time
provide measurements of the height and possibly gap-fraction of vegetation
canopies. This advancements in the characterization of the geometry of vege-
M. Menenti
led Menenti (1984) to new insights in the hydrology of groundwater reservoirs in
the Sahara, confinned by follow up investigations in the Western Desert of Egypt
(Bastiaanssen and Menenti, 1990). The SEBAL algorithm described by Bastiaanssen (1995) was applied to assess irrigation perfonnance in the Nile Delta by Bastiaanssen et al. (1992). Seguin et al. (1991) applied the linear relationship approach to produce an indicator of drought conditions in agricultural areas in
France over a three years period.
Examples and additional references on applications are given in Chap. 17.
8.8 Current and Future Observations
The techniques and applications reviewed in the previous chapter span a period of
time during which there has been a significant evolution in sensor technology.
Changes in the type of measurements obtained with earth observation satellites
have been limited. A major technological evolution of airborne sensors has taken
place however. The driving force of such evolution has been the development of
the new International Earth Observing System (IEOS), a very diverse suite of instruments developed by space agencies: NASA, ESA, NASDA and CNES. In
many cases a series of forerunners of the sensors scheduled for flight in the time
frame 1999 - 2005 has been developed to test new technological solutions. The
extent and direction of technological evolution can be documented by looking at
three categories: current satellite sensors, current airborne sensors and future satellite sensors. For accurate and detailed infonnation on missions and satellites for
earth observation the reader is referred to Kramer (1994). See also appendices to
Chap. 20.
Remote sensing studies ofland evaporation have been hampered by the lack of:
simultaneous and accurate measurements of surface albedo and temperature at
spatial resolutions consistent with the spatial variability of terrestrial landscapes;
measurements of the geometry of canopies to detennine surface roughness and
aerodynamic resistances;
measurements ofPBL conditions.
The near future bears promises of significant improvements on all three aspects:
The ASTER sensor system on-board Terra-l (NASA EOS AM-I) will provide sufficient spectral sampling in the VNIR (Visible - Near Infrared) region
to detennine albedo, while the multi-spectral TIR measurements will provide
for the first time a real opportunity for simultaneous detennination of surface
temperature and emissivity.
The Vegetation Canopy Lidar (NASAl ESSP/ VCL) will for the first time
provide measurements of the height and possibly gap-fraction of vegetation
canopies. This advancements in the characterization of the geometry of vege-