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Title
Remote sensing for resources development and environmental management
Author
Damen, M. C. J.

186
In a first order approximation (9) can be written as:
2 2
Y = F.(4ak cos 0)
for a « X/4ttcos0
We see that for low frequencies and large incidence
angles only the product of moisture content and rough
ness, contained in F.a can be determined.
We selected three bare or barely vegetated fields
and will compare the gamma versus incidence plots
with equality (9). The first results of the applica
tion of the described model are presented in fig. 8.
Corresponding field parameters of interest are given
in table 1.
FIELD: 1
Incidence angle —>
field: 6
Incidence ANGLE >
FIELD: 15
Incidence angle —>
Figure 8. Comparison between the calculated backscat-
tering coefficient for field 1, 6 and 15 and relation
(9) for large incidence angles.
Table 1. Characteristic field parameters.
Field
a
F (dB)
Mg(g/g)
1
40
-10
0.34
6
11
- 5
0.36
15
11
- 3
0.42
In this table we see the rms roughness parameter a
as measured during the ground data collection and
the model parameter F found for field 1, 6 and 15
along with the measured gravimetric water content,
M , in terms of gram water per gram dry soil.
As expected, F and M do exhibit a similar behavior.
It must be stated though that the relationship between
the intensity factor and the gravimetric water content
needs more investigation. Comparison of the results
for the same fields on two succeeding days might shed
some more light on this relationship. In this however
we are restricted by fact that only large moisture
contents were present during the SIR-B experiment.
The large values of gamma observed in fig. 8 for
small incidence angles are caused by a coherent con
tribution which has to be added with the right side
of equation (9). This coherent term is best under
stood if we consider a perfectly conducting flat
surface that appears to the radar as a mirror from
which the main contribution to the received power
comes from nadir. At the intersection angle of the
incoherent term of eq. (9) and the coherent term the
backscattering coefficient exhibits the least depen
dence on roughness (Ulaby 1979) . Because of this
fact and eq. (10) also the behavior of y for small
incidence angles will have to be taken into consider
ation in future investigations in spite of the bad
resolution here.
6 CONCLUSIONS
It is possible to use the data gathered in the SIR-B
project with DUTSCAT working at 1.2 GHz as an extra
source in the semi-empirical solution of the inter
action problem of microwaves with various types of
agricultural fields and the question how to extract
information from this interaction. We must note
however that the data set is rather limited in soil
moisture variation and inherent to the airborne si
tuation not very accurate for small incidence angles
At this moment a variety of aspects is studied more
closely.
REFERENCES
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