ıltivated-
ation.
ge. The
ified as
that they
raneous
ermal-IR
ultivated
| shown.
ge. The
ified as
e snow-
in mixed
ther and
spectral
240
220F
9 200+
= - 4
2 180r "Si
pre EX }
160F ^N —min 3
[ A ]
140 F X j
| M se 7
A A À. A N. A À J
1 2 3 4. 5
Band Number
Figure 8: spectral signature of snow.
CLOUD
E
200 P ^P y A ; -
150 mE Se / / mmyen-stdey
- À N A 1 -
Soo wNNON Min
= [ >. cn pd p y ‘ "
100 + SX, [y H
à}
1
+
ted 2 4
2
mi
Band Number
Figure 9: spectral signature of cloud.
180 oe QOL x:
[ Ean du
160r Of : E
r 7. // — —-mean ]
140 4
> F yt hi ded mean—st.dev -
a 1
> - 7 U^ 1
190 fe / / 5 -
ERGO AS sone A
ü / *
80L———— / _~ e
jut d
Bob TT 3
1 2 5
3
Band Number
Figure 10: spectral signature of green.
Figures 8 9 and 10 clearly explain why mixed pixels (snow
+green) are classified as clouds and table 1 contains band
by band mean values for snow, green and clouds. In the
last column of table 1 there are, band by band, the mean
values between snow and green that are good
approximations for mixed pixels in case of 50% snow and
50% green pixels. In the bands 3, 4 and 5 the
(snow+green) mean values are more similar to clouds
mean values than to snow and green mean values. This is
the explanation of why snow+green mixed pixels are
classified as clouds.
Even using a 2096 threshold these mixed pixels are
classified as clouds because their behaviour is in a very
good agreement with the clouds one.
Band snow + wood
(micron) | Snow Green | Cloud 2
1: 180.10 | 89.28 | 177.72 134.69
|
0.50-0.68 +3.02 | +2542 | +5.18
2: 177.70 | 87.88 | 176.21 132.79
0.725-1.10 +947 | +1528 | +1264
3 197.02 | 153.04 | 70.95 175.03
3.55-3.93 12848 | £11.61 | 219.00
4:1 200.68 | 151.59 | 196.87 176.135
0.30-11.30 120.67 | £15.46 | 129.78
8: 201.16 | 150.32 | 199.88 175.74
|
| 11.50-12.50 +20.46 | +17.36 | +26.00
Table 1: mean value of snow, green and clouds spectral
signatures band by band. Last column shows mean
values for pixels 50% snow and 50% green covered.
6. SYNTHETIC BANDS OBTAINED FROM LINEAR
TRANSFORMATION
In the visible range the mixed pixels behaviour is not liable
to be confused with the clouds one; and so, in order not to
confuse the snow+green mixed pixel with the clouds ones
two new synthetic bands are created (band;s and band2s).
The two bands are obtained as results of the two following
mathematical operations:
bandıs = band,
bands
band», = band,
bands
The above described synthetic channels band;, and
bando, are obtained with a linear transformation and so
the digital number distribution does not change.
Using the new synthetic bands the signatures become the
following (Table 2):
| Snow + green
Band | Snow | Green Cloud 7
| |
| 09209 | 05806 | 2.7569
| band, 0.7507
| bands +0.141 | + 0.1238 | +1.1853
1.0275 0.9926 | 3.0861
E 1.010
| band; 10.083 | 40.0901 | 21.5090
Table 2: the signatures of snow, green and clouds in the
synthetic bands.
The behaviour of snow*green mixed pixels is quite
different from the clouds behaviour and so no confusion
can be made whit clouds.
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 331
