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Daily NDVI relationship to clouds. TANG , Qiuhong The University of Tokyo IIS, OKI’s Lab. PUB. P rediction in U ngauged B asins Relatively reliable P rediction in U n-ground-gauged B asins. Ungaused Basin B. Ungauged Basin A. PUB and observation. - PowerPoint PPT Presentation
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Daily NDVI relationship to clouds
TANG , Qiuhong
The University of Tokyo
IIS, OKI’s Lab.
PUB
Prediction in Ungauged Basins
Relatively reliable Prediction in Un-ground-gauged Basins
UngaugedBasin A
UngausedBasin B
PUB and observation
If there isn’t information of the basins, we cannot estimate hydrological response.
“UNGAUGED” (Un-ground-gauged)
Indirectly ‘gauge’ (observation/information)
Remote sensing Similar climate zone data
What’s gauged? What’s ungauged? What’s PUB?
PUB started with the geophysical science.
PUB model forcing data“UNGAUGED”
Remote sensing Similar climate zone data
Available for RS
Describe Land Surface
DEM, Land Cover, …
Unavailable for RS
Temperature, Wind speed
Vapor pressure…
DEM: geomorphologic factor to hydrological response
Land Cover: vegetation phonology to hydrological response
Wind speed, vapor pressure etc. : regional climate forcing
RS
Interpolate
RS: Unreliable, distributed data | Ground observation: Reliable, point data
Land Cover: NDVI data
NDVI = (NIR-Red) / (NIR+Red) NDVI (normalized difference vegetation index)
cloud
Satellite NDVI
‘True’ NDVI
Cloud Index (NCI)
-0.2
0.0
0.2
0.4
0.6 NDVIr (Real time NDVI) NDVIc (Corrected NDVI)
ND
VI =
(N
IR-R
ed)/
(NIR
+R
ed)
Time (day)
NDVImin
'Drop of NDVI' caused by Cloud&Aerosols etc.
NCAI = (NDVIr -NDVImin) / (NDVIc -NDVImin) [0, 1]
Cloud Index from Ground Observation
Cloud Amount Sunshine Index = n/N
Where, n is duration of sunshine and N is maximum possible sunshine
Comparison (Satellite & Ground Based Cloud Index)
R-squared value between daily NCI values and the observed cloud amount (Left) and Sunshine time index (right). (1995-2000, 120 stations)
0 20 40 60 80 100 1200.0
0.1
0.2
0.3
0.4
0.5
0.6
Mean R2 = 0.40741SD = 0.06817
R2
Clo
ud A
moun
t - N
CA
I (R
2)
Stations
0 20 40 60 80 100 1200.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
R2
Suns
hin
e -
NC
AI R
2Stations
Mean R2 = 0.50377SD = 0.07033
Comparison (Satellite & Ground Based Cloud Index)
RMSE value between daily NCI values and the observed cloud amount (Left) and Sunshine time index (right). (1995-2000, 120 stations)
0 20 40 60 80 100 1200.00
0.05
0.10
0.15
0.20
0.25
0.30
Mean RMSE = 0.25754SD = 0.01379
RMSE
Clo
ud A
mount -
NC
AI (
RM
SE
)
Stations
0 20 40 60 80 100 1200.00
0.05
0.10
0.15
0.20
0.25
Mean RMSE = 0.20653SD = 0.01338
RMSE
Sunsh
ine -
NC
AI (
RM
SE
)
Stations
Comparison (Satellite & Ground Based Cloud Index)
R-squared value between daily NCI values and the observed cloud amount (Left) and Sunshine time index (right). (1995-2000)
The poorest relationship in the Tibet Plateau (red circle) might due to the distortion of satellite scans.
.00-.09
.09-.25
.25-.36
.36-.49
.49-.64
.00-.09
.09-.25
.25-.49
.49-.64
.64-.81
Satellite data vs. Interpolate to all over the River Basin
Comparison (R2)
Distribution of R-squared values over the study area. NCI and Cloud Amount Index (left), NCAI and Sunshine Index (right).
>
80%
>
90%
Comparison (RMSE)
The root-mean-square error (RMSE) associated with NCI and cloud amount ranges from 0.21 to 0.30 with an averaged value of 0.25.
For Sunshine time, RMSE ranges from 0.16 to 0.26 with an averaged value of 0.20.
ComparisonUSGS Land use
The daily NCI versus observed cloud amount and SCAI relationships are strong and land cover independent expect for water body
Conclusion The NCI and observed cloud index retain a high
correlation coefficient suggesting that NCI may be useful for estimating clouds influence to solar radiation.
Satellite data
(NDVI)
Solar radiation
Ground based observation
(cloud amount, sunshine)
Thank you for your attention.Thank you for your attention.
Solar and Scan Geometry
Sunshine – NCI a Sunshine – NCI b