2
Physical Principles and Technical Aspects
of Remote Sensing
Helmut Rott
Institut fUr Meteorologie und Geophysik
UniversiUit Innsbruck. A-6020 Innsbruck, Austria
2.1 Introduction
Remote sensing refers to the extraction of information about an object without physical contact. The discussion in this chapter is restricted to remote
sensing by means of electromagnetic radiation, which is the main carrier of
information for earth observation from space. Passive sensing utilizes natural
radiation sources: the radiation emitted from the earth's surface and atmosphere or reflected solar radiation. For active sensing the object of interest
(the target) is illuminated by an artificial source of electromagnetic radiation,
the reflected signal received by the sensor is recorded and analyzed.
Remote sensing involves the interpretation of measurements of electromagnetic radiation which is received by a detector after interacting with a
target. In general this represents an inverse problem with no unique solution
because the observed medium is characterized by a number of physical parameters, various states of which may lead to the observed radiation signature.
This means that some kind of a priori knowledge is crucial for solving the inverse problem. For this purpose it is necessary to understand the interaction
mechanisms of electromagnetic radiation with the objects of interest.
2.2 The Electromagnetic Spectrum and Radiation
Laws
The main spectral regions for earth observation from space are the visible
(VIS), the infrared (IR), and the microwave (MW) region. The corresponding wavelengths and frequencies are shown in Fig. 2.1. Various, more or less
arbitrary, subdivisions of the IR region are used, including solar (or shortwave) IR (O.75-4/Lm) and terrestrial (or thermal) IR (>4/Lm), or near, middle,
and far IR. In the microwave region various schemes of letter designation for
bands exist. The most common set of microwave band designations is shown
in Fig. 2.1. Spaceborne imaging radars operate in the L-, S-, C-, and X-bands,
whereas microwave radiometry for earth surface observations utilizes mainly
the K-and W-bands.
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000
Physical Principles and Technical Aspects
of Remote Sensing
Helmut Rott
Institut fUr Meteorologie und Geophysik
UniversiUit Innsbruck. A-6020 Innsbruck, Austria
2.1 Introduction
Remote sensing refers to the extraction of information about an object without physical contact. The discussion in this chapter is restricted to remote
sensing by means of electromagnetic radiation, which is the main carrier of
information for earth observation from space. Passive sensing utilizes natural
radiation sources: the radiation emitted from the earth's surface and atmosphere or reflected solar radiation. For active sensing the object of interest
(the target) is illuminated by an artificial source of electromagnetic radiation,
the reflected signal received by the sensor is recorded and analyzed.
Remote sensing involves the interpretation of measurements of electromagnetic radiation which is received by a detector after interacting with a
target. In general this represents an inverse problem with no unique solution
because the observed medium is characterized by a number of physical parameters, various states of which may lead to the observed radiation signature.
This means that some kind of a priori knowledge is crucial for solving the inverse problem. For this purpose it is necessary to understand the interaction
mechanisms of electromagnetic radiation with the objects of interest.
2.2 The Electromagnetic Spectrum and Radiation
Laws
The main spectral regions for earth observation from space are the visible
(VIS), the infrared (IR), and the microwave (MW) region. The corresponding wavelengths and frequencies are shown in Fig. 2.1. Various, more or less
arbitrary, subdivisions of the IR region are used, including solar (or shortwave) IR (O.75-4/Lm) and terrestrial (or thermal) IR (>4/Lm), or near, middle,
and far IR. In the microwave region various schemes of letter designation for
bands exist. The most common set of microwave band designations is shown
in Fig. 2.1. Spaceborne imaging radars operate in the L-, S-, C-, and X-bands,
whereas microwave radiometry for earth surface observations utilizes mainly
the K-and W-bands.
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000