Geography Reference
In-Depth Information
-Image Radarsat-2 Fine Quad-Pol (10/02/2011); Source: VIGISAT (Brest)
A
-Color composite:
Red
: HH;
Green
:
Blue
: W
3
°
36W
3
°
33W
3
°
45W
3
°
30W
48
°
45N
(b)
N
N
1
(a)
48
°
39N
48
°
30N
2
5
0
5 Km
3
B
- Color composite (Freeman decomposition)
-Red
: Power contributions due to rough surface;
-
Green
: Power contributions due to volume scattering;
-Blue
: Power contributions due to double-bounce
−
1-Water:
Specular scattering;
−
2-Riparian vegetation:
volume scattering;
−
3-Bare soil:
rough surface scattering;
0.5
0
0.5 Km
Figure 10.10
Riparian vegetation characterisation with a Radarsat-2 (
) image. Fine Quad-Pol on the Yar watershed in Brittany
(France; 10/02/2010), at a. large and b. fine scales see text for detail. Radarsat-2
©
©
image.
Figure 10.10 presents a composite colour of a polari-
metric Radarsat-2 image in France (Brittany) at the end
of February 2010. Bare soils are represented in magenta
and blue because of high backscattering in HH ampli-
tude band (sensitive to surface scattering). Vegetation,
characterised by volume scattering, appears here in green,
as the highest backscattering for high vegetation such
as riparian vegetation is measured for the HV polari-
sation. With this type of data compounded with four
polarisations, different polarimetric decomposition can
be applied (Cloude and Pottier, 1997; Touzi et al., 2007,
Freeman et al., 2007) and allow a good discrimination of
geometrical parameters of the studied object as the type
of scattering (surface, volume or double bounce). Inverse
model can also be applied to retrieve soil or vegetation
moisture, forest biomass etc (Beaudoin, 1994).
10.5.3.3 Frequencies
Three main wavelengths are generally used by SAR
satellites: X band (2.4 to 3.75 cm) for cartography, C
band (3.75 to 7.5 cm) for agricultural monitoring, land
use and land cover changes and L band (15 to 30 cm)
for forestry, geology, etc. The longer the frequency,
the deeper the wavelength can penetrate the soil or the
vegetation. Thus, each wavelength has its specificities,
for example the L band present on the Alos-Palsar
satellite deeply penetrates the canopy and provides useful
information for the discrimination of different vegetation
types (Hess et al., 1990; Izzawati et al., 2006).The
signal of the radar back to the satellite is called the
backscattering coefficient (measured in dB), it depends
on the soil moisture, the roughness and the geometrical
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