GE
is of both
whole sky
with map
jection. In
id levelled
ere) image
| the image
on (3).
(3)
; on whole
dinates (u,
1e ground-
whole sky
given the
| type, and
>d to map
of fisheye
ft out of
emisphere
5).
(4)
G)
v (pixels)
| has 1650
(R) is 825
24, 824) in
image, the
ed to map
coordinates using zenith (0) and azimuth (4) angles by given
any cloud heights approximately. Generally, lower clouds such
stratocumulus appears from near the ground to 2km and in case
of cumulus, it appears from 0.6 to 6km.
The conversion from the each pixel (uj vj) of cloud area on
whole sky image to map coordinates (x; y;) can be shown in
equation (6) and (7).
HD; = tan 0i x CHapr (6)
x; = sine; x HD; + Ke
(7)
yi = cos p; X HDit yo
where — HD; ; the horizontal distance from ground-based
cloud observation point (m)
CH,,, ; approximate cloud height (m)
X;, y;; map coordinates of image coordinates u;, v; (m)
Xo» Yo ; map coordinates of ground-based cloud
observation point (m)
4. RESULT AND DISCUSSSION
As one of experiment, we examine to compare and overlay with
several whole-sky images of different cloud types and those
synchronous Terra & Aqua/ MODIS images observed in central
Kyoto, Japan. The grand-based cloud observation point is
located at (N35.018243°, E135.768278°). In this experiment,
we use UTM (Zone53N, WGS84) as map projection.
Figure 2 shows one of the results of cloud discrimination from
whole sky images taken at 12:54 and 12:56 on Aug. 26^ 2005.
Aug. 26, 2005 at 12:56 (JST)
Figure 2. Results of sky classified image (right) from whole sky
images (left) of 2-minutes different images.
Cloud discrimination area is painted as light green on whole sky
image. Red circle shows the area of zenith angle less than 65
degrees.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Red circle corresponds to the area of zenith angle less than 65
degrees. Cloud type is recognized as cumulus of small size
visually. Also cloud type such cumulus and stratocumulus have
low SI, very close to SI = 0, and high BI values digitally.
Outside of this red circle seems to overestimate cloud coverage
because of the long pass of atmospheric layer from the view at
large zenith angle. Here, the target area is in less than 65
degrees of zenith angle.
Figure 3 shows Aqua/ MODIS observed at 12:55(JST) on Aug.
26^ 2005 as one of the sample satellite images in this
experiment.
Figure 3. Aqua/ MODIS VIS (ch.1) and NIR (ch.2) composite
image (RGB: ch.1,2,1) with 250m ground resolution observed at
12:55(JST) on Aug. 26", 2005.
Red x is the point of ground-based cloud observation. Red circle
indicates the overlaying area with zenith angle less than 65
degrees in case of HD calculation as CH, = 2000m.
There are not seen so much cloud coverage around the
observation point by comparing with northern part of this
MODIS image. However, it is certainly confirmed the clouds
existence in the red circle visually.
For overlaying clouds area, the horizontal distribution of
cumulus clouds area discriminated from whole sky image are
calculated in four cases of CH, = 600, 1000, 1500, 2000m by
considering general cloud height of cumulus firstly. After
calculations, it is the best fit to both ground and satellite-based
images in the case of CH, = 2000m.
Figure 4 shows the results of overlaying the cumulus clouds
area discriminated from whole sky images taken at 12:54 and
12:56 (figure 2) to Aqua/ MODIS observed at 12:55 on Aug.
26^ 2005 (figure 3). Legend colors show SI value calculated
from whole sky image. SI in almost clouds area shows very low.
