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shown that wavelengths 0.8 and 3.4 cm register radio-brightness contrasts
ʔ
T
b
∈
[200,
300]
K. The most important fact is that microwave range is sensitive to the surface
temperature change what allows the detection of heat sources on the peat bogs and in
forests. It is indicated that microwave monitoring of peat bogs and forests can detect the
°
fire point with warning.
In common case, passive radiation of the surface registered at the wavelengths
ʻ
1
and
ʻ
2
gives
ʔ
T
b
≈ ʺʔ
zdT
s
/dz where
ʔ
z = z
2
-
z
1
(z
2
> z
1
) is the difference of the
depth between sub-surface layers, dT
s
/dz =
−
Q/k
T
, Q is the heat
fl
flux intensity, kT
T
is
the thermal-conductivity coef
cient for layer
ʔ
z. SHF-radiometer sensitivity usually
equals dT
s
/dz
/m. It allows measurement of water content in vegetation
biomass what gives the possibility to assess
≈
0.1
1.0
°
-
fire dangerousness using corresponding
models. Effectiveness of microwave monitoring of forested areas depends on the
model structure of vegetation environment. Ground
fire is the most problematic
object for its detection because of presence of radiation attenuation in the vegetation
cover. Multi-channel sensing promotes the solution of many tasks, arising here, by
means of cluster analysis application.
Use of three-layers model of the
fl
flame-smoke-tree crown gives
ʱ
P
=(1
-
exp
{
−ʺ
1
})exp(
−ʺ
2
) exp(
−ʺ
3
) where
ʱ
P
is the emissivity of
fireplace of the lower forest
ʺ
I
is the attenuation coef
flame radiation (i = 1), smoke (i = 2) and the
whole of crown (i = 3). Attenuation coef
re,
cient for
fl
cient of tree crown is function of tree
types. It is determined that absorption in crown grows strongly with decrease of
wavelengths. Figure
2.16
shows a dependence of radio-brightness contrasts from
wavelengths.
Observations show that statistical characteristics of SHF-radiation for forested
areas are changed with growth of
fire readiness for layers of combustible forest
materials. As an example, such dependence can be written in the form (Yakimov
1996):
T
b
¼
jðk;
w
Þ
T
s
ð
1
exp
faðk;
w
Þ
h
gþ
T
bs
exp
faðk;
w
Þ
h
g;
Fig. 2.16 Averaged spectr of radio-brightness contrasts for separate elements of the forest fire:
1
—
smoked zone, 2
—
fire front, 3
—
burned-out zone, 4
—
re back, 5
—
boundary between fire front
and burned-out zone
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