1 Introduction
13
all calibrated with the aid of observed data, e.g. rainfall, runoff, evaporation etc.
The hydrological variable having the most significant influence on hydrological
processes is, however, the state of soil moisture in space and time. Soil moisture
determines, how much water goes up from an area element (evaporation, transpiration, interception), how much goes down (infiltration, percolation) and how
much water moves laterally (surface runoff, interflow, groundwater flow). Due to
the limited data situation in hydrology, this most important parameter soil moisture is almost never measured in the field. Therefore it occurs in hydrological
models in the form of a residual. This fact is certainly one of the reasons, why the
performance of so many hydrological models is unsatisfactory. It can be hoped,
that in the near future remote sensing will allow to measure soil moisture with an
acceptable resolution in time and space and with an appropriate accuracy. If this
becomes operational, the time has arrived for the development of completely new
- and hopefully better - hydrological models, in which soil moisture becomes the
central parameter instead of a residual and the information required for model
calibration and validation will come from remote sensing sources. It can also be
expected, that in many other fields of hydrological modeling the existing or expected availability of remote sensing information will lead to the development of
much more efficient hydrological models.
1.6 Structure of the Book
It is surprising that there are very few books or compendiums that cover the complete subject of remote sensing in hydrology and water management, where as
there are many books on hydrology and water resources management. The number
dealing with hydrology can be easily counted on one hand, Wiesnet et aI, 1979,
Schultz and Barrett, 1989, Engman and Gurney, 1991, Rango, 1994, and a soon to
be published compendium by Rango and Shalaby. All except the Engman and
Gurney book have been sponsored by International organizations such as the UN
and WMO. Only the Schultz and Barrett publication addressed water resources
management. There have been many advances both in instrumentation and applications since the last of these have been published and there is an urgent need to
provide an updated source to the hydrology and water management communities.
Since this book is not meant to be a textbook with problem and examples, but
rather a reference book in which information on any aspect of interest can easily
be found, the book is sub-divided into four general sections, each of which is
again sub-divided into various chapters. The sections are as follows:
Section I: Overview and Basis Principles
Section II: RS Application to Hydrological Monitoring and Modeling
Section III: Water Management with the Aid ofRS Data
Section IV: Future Perspective.
The first section provides general principles and techniques which should be understood in order to recognize what remote sensing can - and cannot - deliver.
Section II is devoted to hydrology, while Section III deals with water management
problems. Section IV gives some information on potential future developments in
13
all calibrated with the aid of observed data, e.g. rainfall, runoff, evaporation etc.
The hydrological variable having the most significant influence on hydrological
processes is, however, the state of soil moisture in space and time. Soil moisture
determines, how much water goes up from an area element (evaporation, transpiration, interception), how much goes down (infiltration, percolation) and how
much water moves laterally (surface runoff, interflow, groundwater flow). Due to
the limited data situation in hydrology, this most important parameter soil moisture is almost never measured in the field. Therefore it occurs in hydrological
models in the form of a residual. This fact is certainly one of the reasons, why the
performance of so many hydrological models is unsatisfactory. It can be hoped,
that in the near future remote sensing will allow to measure soil moisture with an
acceptable resolution in time and space and with an appropriate accuracy. If this
becomes operational, the time has arrived for the development of completely new
- and hopefully better - hydrological models, in which soil moisture becomes the
central parameter instead of a residual and the information required for model
calibration and validation will come from remote sensing sources. It can also be
expected, that in many other fields of hydrological modeling the existing or expected availability of remote sensing information will lead to the development of
much more efficient hydrological models.
1.6 Structure of the Book
It is surprising that there are very few books or compendiums that cover the complete subject of remote sensing in hydrology and water management, where as
there are many books on hydrology and water resources management. The number
dealing with hydrology can be easily counted on one hand, Wiesnet et aI, 1979,
Schultz and Barrett, 1989, Engman and Gurney, 1991, Rango, 1994, and a soon to
be published compendium by Rango and Shalaby. All except the Engman and
Gurney book have been sponsored by International organizations such as the UN
and WMO. Only the Schultz and Barrett publication addressed water resources
management. There have been many advances both in instrumentation and applications since the last of these have been published and there is an urgent need to
provide an updated source to the hydrology and water management communities.
Since this book is not meant to be a textbook with problem and examples, but
rather a reference book in which information on any aspect of interest can easily
be found, the book is sub-divided into four general sections, each of which is
again sub-divided into various chapters. The sections are as follows:
Section I: Overview and Basis Principles
Section II: RS Application to Hydrological Monitoring and Modeling
Section III: Water Management with the Aid ofRS Data
Section IV: Future Perspective.
The first section provides general principles and techniques which should be understood in order to recognize what remote sensing can - and cannot - deliver.
Section II is devoted to hydrology, while Section III deals with water management
problems. Section IV gives some information on potential future developments in