updating of existing maps, projects planning and decision-making. This phenomenal growth in the field of RADAR remote sensing is due to the successful launching
of series of satellites.
The digital SAR processing is referred to the correlation process thereby the
SAR signal use to extract the optimum Doppler returns. Digital SAR processors
allow the user to specify additional processing options which may include slantrange to ground-range conversion, range dependent gain correction, the number of
independent looks in the azimuth dimension, or pixel spacing. These can also be
applied in the post-image generation phase. The general theory behind these
techniques is presented in this chapter, followed by an introduction of various
digital enhancement techniques that may be applied by an image analyst using a
digital image analysis system and suitable computer software packages.
14.1.1 Why Do We Use Radar Remote Sensing?
Nowadays, everyone is trying to work effectively on remote sensing and understanding of various applications of this technology. This is because, we can reduce
the time and cost in a project. In addition, for the places that are inaccessible remote
sensing can be implemented effectively to detect an object we are looking for.
Imaging radars are among the latest additions to a variety of remote sensing
instrument available for analyzing Earth resources and for monitoring the environment. So far, the results obtained from many application oriented Research and
Development (R&D) studies and from the operational use of airborne imaging
radars are encouraging. But knowledge regarding the full extent of their capabilities
and applications of radar remote sensing are still relatively limited compared to the
experience with established techniques such as aerial photography and optical
remote sensing techniques from space, e.g. LANDSAT TM, SPOT (Drury 1987;
Ulaby 1989; Ali and Pirasteh 2004; Avery and Berlin 1992; Bu ¨rgmann et al. 2000;
CCRS 2004, 2006; Pirasteh et al. 2009). So, why do we use radar?
The answer to this question is threefold. A very valid reason for using radar,
from an operational point of view, is its all-weather imaging capability, since
microwaves can penetrate cloud and any weather condition. Radars operating at
wavelengths greater than 2 cm are not significantly affected by cloud cover,
whereas rain does become a considerable factor for systems imaging at wavelengths below 4 cm. Furthermore, imaging radar operates independently of sun
illumination, since it provides its own scene illumination as an active remote
sensing system. The radar images have more potential to extract the information
in haze climate conditions. This makes the advantages of using radar images
(Goldstein 1997).
Microwaves also have the ability to penetrate a surface layer, for example, a
vegetation canopy, more deeply than optical wavelengths can. However, there are a
number of limiting factors (Goldstein 1997) to consider, since the extent of penetration is determined by the moisture content and the density of the vegetation on
one hand, and by the wavelength of the radar and its viewing geometry on the other.
282
S. Pirasteh et al.
of series of satellites.
The digital SAR processing is referred to the correlation process thereby the
SAR signal use to extract the optimum Doppler returns. Digital SAR processors
allow the user to specify additional processing options which may include slantrange to ground-range conversion, range dependent gain correction, the number of
independent looks in the azimuth dimension, or pixel spacing. These can also be
applied in the post-image generation phase. The general theory behind these
techniques is presented in this chapter, followed by an introduction of various
digital enhancement techniques that may be applied by an image analyst using a
digital image analysis system and suitable computer software packages.
14.1.1 Why Do We Use Radar Remote Sensing?
Nowadays, everyone is trying to work effectively on remote sensing and understanding of various applications of this technology. This is because, we can reduce
the time and cost in a project. In addition, for the places that are inaccessible remote
sensing can be implemented effectively to detect an object we are looking for.
Imaging radars are among the latest additions to a variety of remote sensing
instrument available for analyzing Earth resources and for monitoring the environment. So far, the results obtained from many application oriented Research and
Development (R&D) studies and from the operational use of airborne imaging
radars are encouraging. But knowledge regarding the full extent of their capabilities
and applications of radar remote sensing are still relatively limited compared to the
experience with established techniques such as aerial photography and optical
remote sensing techniques from space, e.g. LANDSAT TM, SPOT (Drury 1987;
Ulaby 1989; Ali and Pirasteh 2004; Avery and Berlin 1992; Bu ¨rgmann et al. 2000;
CCRS 2004, 2006; Pirasteh et al. 2009). So, why do we use radar?
The answer to this question is threefold. A very valid reason for using radar,
from an operational point of view, is its all-weather imaging capability, since
microwaves can penetrate cloud and any weather condition. Radars operating at
wavelengths greater than 2 cm are not significantly affected by cloud cover,
whereas rain does become a considerable factor for systems imaging at wavelengths below 4 cm. Furthermore, imaging radar operates independently of sun
illumination, since it provides its own scene illumination as an active remote
sensing system. The radar images have more potential to extract the information
in haze climate conditions. This makes the advantages of using radar images
(Goldstein 1997).
Microwaves also have the ability to penetrate a surface layer, for example, a
vegetation canopy, more deeply than optical wavelengths can. However, there are a
number of limiting factors (Goldstein 1997) to consider, since the extent of penetration is determined by the moisture content and the density of the vegetation on
one hand, and by the wavelength of the radar and its viewing geometry on the other.
282
S. Pirasteh et al.