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M. Menenti
management problems tend to establish areas with open water and salt deposits, all
of which clearly identifiable with simple techniques and multispectral imagery.
This potential has yet be fully brought to bearing, however. It is fair to say that
land cover mapping in different forms has reached the status of an operational
technique of which most irrigation professionals in most countries are fully aware.
The situation is rather different as regards other techniques and applications
described in this chapter. Although there are examples of applications of e.g.
thermal infrared observations at a scale consistent with real applications, these
more advanced techniques are still somewhat removed from the real world of
irrigation and drainage. One obvious explanation is that quantitative use of thermal
infrared and microwave observations require a solid scientific background and a
level of specialization not readily available to irrigation professionals. Another less
obvious reason is that the overriding requirement is timeliness of the observations.
As regards land cover, timely observation means once or twice during an irrigation
season. As regards e.g. crop water stress, timeliness means one day from data
acquisition to actions undertaken. Since daily observations are only available at
relatively low spatial resolution, use of this information gets out of the picture for
the operation of farms and small to medium-sized irrigation schemes. Large
irrigation schemes, conversely, might benefit from the use of near-real time
information except that the operation of such systems is a slow and complex
process.
The above remarks lead to two avenues where true applications might be
developed:
A. Analyse and possibly remove the constraints which limit the use of low
resolution data in extensive irrigation schemes. In the next few years several
sensors will be flown to collect data at medium and low resolution with global
coverage achieved in one to three days. Many sensors, e.g. MODIS and
MERIS, can provide useful observations with significantly improved spectral
and radiometric characteristics.
B. Develop smaller and lighter sensors usable for cheap single-user data
collection and analysis. Current technology provides the opportunity of
developing reasonably advanced sensors having very limited mass and size.
There are already examples of multispectral cameras and radiometers flown
onboard model aircraft:s which have been used as a true user-oriented and
affordable service to farmers.
References
Allen, R.O., M. Smith, A .. Perrier and L.S. Pereira, 1994. An update for the definition of
reference evapotranspiration. ICID Bull. Vol. 43(2): 1-34; 35-92
Azzali S. and Menenti M., 1989. Application of remote sensing to irrigation water management
in two Italian irrigation districts. in: Calabresi O. and Ouyenne D. (eds.): European coordi-
M. Menenti
management problems tend to establish areas with open water and salt deposits, all
of which clearly identifiable with simple techniques and multispectral imagery.
This potential has yet be fully brought to bearing, however. It is fair to say that
land cover mapping in different forms has reached the status of an operational
technique of which most irrigation professionals in most countries are fully aware.
The situation is rather different as regards other techniques and applications
described in this chapter. Although there are examples of applications of e.g.
thermal infrared observations at a scale consistent with real applications, these
more advanced techniques are still somewhat removed from the real world of
irrigation and drainage. One obvious explanation is that quantitative use of thermal
infrared and microwave observations require a solid scientific background and a
level of specialization not readily available to irrigation professionals. Another less
obvious reason is that the overriding requirement is timeliness of the observations.
As regards land cover, timely observation means once or twice during an irrigation
season. As regards e.g. crop water stress, timeliness means one day from data
acquisition to actions undertaken. Since daily observations are only available at
relatively low spatial resolution, use of this information gets out of the picture for
the operation of farms and small to medium-sized irrigation schemes. Large
irrigation schemes, conversely, might benefit from the use of near-real time
information except that the operation of such systems is a slow and complex
process.
The above remarks lead to two avenues where true applications might be
developed:
A. Analyse and possibly remove the constraints which limit the use of low
resolution data in extensive irrigation schemes. In the next few years several
sensors will be flown to collect data at medium and low resolution with global
coverage achieved in one to three days. Many sensors, e.g. MODIS and
MERIS, can provide useful observations with significantly improved spectral
and radiometric characteristics.
B. Develop smaller and lighter sensors usable for cheap single-user data
collection and analysis. Current technology provides the opportunity of
developing reasonably advanced sensors having very limited mass and size.
There are already examples of multispectral cameras and radiometers flown
onboard model aircraft:s which have been used as a true user-oriented and
affordable service to farmers.
References
Allen, R.O., M. Smith, A .. Perrier and L.S. Pereira, 1994. An update for the definition of
reference evapotranspiration. ICID Bull. Vol. 43(2): 1-34; 35-92
Azzali S. and Menenti M., 1989. Application of remote sensing to irrigation water management
in two Italian irrigation districts. in: Calabresi O. and Ouyenne D. (eds.): European coordi-