110
Chapter 12
groundwater, and consumption—in time and space—by crops is far less well
known. Further, the spatial and temporal complexity of irrigation systems
themselves makes the analysis of their operational performance extremely
challenging. In a typical medium sized scheme in a developing country, tens
of thousands of farmers each receive perhaps five irrigation events in a
season, with each event having varying characteristics of flow rate and
duration. Establishing a measuring system capable of observing such a
process has challenged a large number of irrigation researchers over the last
decade or more.
4.
EARTH OBSERVATION DEMANDS FOR
IRRIGATED AGRICULTURE
The capacity of remote sensing to identify and monitor vegetation
parameters has undergone impressive improvements during the last 10 years.
Significant research efforts have been undertaken to better explore the
potential that satellite measurements offer: objective and spatial data with a
dynamic dimension. The fleet of satellite platforms has been expanded and
the availability of spectrally, spatially and temporally different radiative
properties of the land surface has grown. A major new breakthrough is
expected to occur at the beginning of the next century with the establishment
of space platforms. Although the applications of remote sensing were long
delayed after the launch of satellites in the seventies, it is generally accepted
that the science related to the understanding and interpreting of spectral
signatures progressed rapidly. Review papers on the potential of remote
sensing for irrigation management have been prepared by Menenti (1990),
Vidal and Sagardoy (1995), Thiruvengadachari and Sakthivadivel (1997)
and Bastiaanssen (1998). On the basis of these papers, it may be concluded
that remote sensing provides an opportunity to obtain much of the data
required to improve the management of irrigation and drainage systems.
The current status of research has reached a stage where several
interpretation algorithms have proven their power. Visible and near-infrared
measurements can be combined to obtain a number of agronomic features
that are useful to describe the crop water demands through crop coefficients
(e.g., Ahmed and Neale, 1996), net radiation (e.g., Roerink et al., 1997) and
transpiration coefficients (e.g., Choudhury et al., 1994). The crop response to
water application can be expressed on the basis of fractional vegetation
cover and leaf area index using vegetation indices calculated from satellite
data (e.g., Choudhury et al., 1994). Complementary information on the
hydrological status can be obtained from thermal infrared measurements to
arrive at crop water stress (e.g., Moran et al., 1994) and crop consumptive
Chapter 12
groundwater, and consumption—in time and space—by crops is far less well
known. Further, the spatial and temporal complexity of irrigation systems
themselves makes the analysis of their operational performance extremely
challenging. In a typical medium sized scheme in a developing country, tens
of thousands of farmers each receive perhaps five irrigation events in a
season, with each event having varying characteristics of flow rate and
duration. Establishing a measuring system capable of observing such a
process has challenged a large number of irrigation researchers over the last
decade or more.
4.
EARTH OBSERVATION DEMANDS FOR
IRRIGATED AGRICULTURE
The capacity of remote sensing to identify and monitor vegetation
parameters has undergone impressive improvements during the last 10 years.
Significant research efforts have been undertaken to better explore the
potential that satellite measurements offer: objective and spatial data with a
dynamic dimension. The fleet of satellite platforms has been expanded and
the availability of spectrally, spatially and temporally different radiative
properties of the land surface has grown. A major new breakthrough is
expected to occur at the beginning of the next century with the establishment
of space platforms. Although the applications of remote sensing were long
delayed after the launch of satellites in the seventies, it is generally accepted
that the science related to the understanding and interpreting of spectral
signatures progressed rapidly. Review papers on the potential of remote
sensing for irrigation management have been prepared by Menenti (1990),
Vidal and Sagardoy (1995), Thiruvengadachari and Sakthivadivel (1997)
and Bastiaanssen (1998). On the basis of these papers, it may be concluded
that remote sensing provides an opportunity to obtain much of the data
required to improve the management of irrigation and drainage systems.
The current status of research has reached a stage where several
interpretation algorithms have proven their power. Visible and near-infrared
measurements can be combined to obtain a number of agronomic features
that are useful to describe the crop water demands through crop coefficients
(e.g., Ahmed and Neale, 1996), net radiation (e.g., Roerink et al., 1997) and
transpiration coefficients (e.g., Choudhury et al., 1994). The crop response to
water application can be expressed on the basis of fractional vegetation
cover and leaf area index using vegetation indices calculated from satellite
data (e.g., Choudhury et al., 1994). Complementary information on the
hydrological status can be obtained from thermal infrared measurements to
arrive at crop water stress (e.g., Moran et al., 1994) and crop consumptive