38, 2012 
reshold values 
X 5 HRG had 
ody extraction 
| Spot 5 HRG 
lid red colour 
t sites in both 
> is larger than 
lanoi City and 
nds, rivers and 
R=green and 
ban including 
Clear water is 
n colour with 
sedimentation 
  
    
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 
To assess accuracy of the water extraction a comparison of 
water extraction result and input image by visual check has been 
made. Figure 9 shows enlargement of West Lake and part of 
Red River on Landsat 5 TM. Water extraction is showed on top 
and colour composite of input image on bottom part. We can 
see that boundaries of main water bodies with large area are 
drawn quite exactly. Some small canals are not fully extracted 
due to low spatial resolution of Landsat 5 TM sensor. 
Small canals 
  
Figure 9. Water body extraction for Landsat 5 TM (top),) and in 
colour composite (bottom) 
Figure 10 shows comparison study for Spot 5 HRG image. All 
water bodies which are widely enough, at least 5 pixels were 
very exactly extracted. Small water area is mixed with 
surrounding ground objects and cannot be extracted. 
  
Figure 10. Water body extraction for Spot 5 HRG (top),) and in 
colour composite (bottom) 
Due to 10 m spatial resolution of the Spot 5 HRG sensor, many 
spectral mixtures occur in the image. The mixture allocated 
mainly in the boundary of water body. Therefore when we 
enlarge enough the result we can see thin unclassified boundary 
around extracted water body. Normally due to low spatial 
resolution the Landsat 5 TM image is suitable for mapping in 
scale 1:100,000 and Spot 5 HRG image for scale 1:50,000. The 
mapping standard requires accuracy of 0.3 mm in map scale for 
  
boundary of all hydrographical features. This requirement is 
easily fulfilled for large area water feature but quite difficult for 
long thin water features. Figure 11 explains in detail this 
phenomenon. 
Mixture due to low 
spatial resolution 
Unclassified 
buffer 
around water 
bodies 
Figure 11. Influence of spatial resolution to accuracy of water 
extraction 
4. CONCLUSION 
The study pointed out some main conclusions as follow: 
- The spectral pattern of water in four spectral bands: 
green, red, NIR and SWIR can be used for water 
extraction. 
- Due to spectral mixture of ground objects caused by 
low spatial resolution water extraction by spectral 
patterns needs to be combined with some other 
measures such as level of reflectance in SWIR band. 
- Even there are unclassified pixels around water body 
or water body which is narrower than 5 pixels in 
width cannot be classified but when we consider 
mapping scale 1:100,000 for Landsat 5 TM and 
1:50,000 for Spot 5 HRG sensors the accuracy 
achieved by this method can be without doubt fairly 
accepted. 
- In the next phase the author would like to extend 
research for Landsat TM and ETM+ data with all 6 
visible bands. 
References: 
Nguyen Dinh Duong, 1997. Graphical analysis of spectral 
reflectance curve. Proc. of ACRS 1997. 
Fu June, Wang Jizhou, Li Jiren, 2007. Study on the automatic 
extraction of water body from TM image using decision tree 
algorithm. Proc. of SPIE Vol. 6625 662502-1. 
Hua Wang, Li Pan, Hong Zheng, 2008. Multi-texture-model for 
water extraction based on remote sensing image. Proc. of 2008 
Congress on Image and Signal processing. IEEE computer 
society. 
Luo, J., Sheng, Y., Shen, Z., Li, J., 2010. High-precise water 
extraction based on spectral-spatial coupled remote sensing 
information. In IGARSS(2010) 2840-2843. 
Rajiv Kumar Nath, S K Deb, 2010. Water-body Area extraction 
form high resolution satellite images — an introduction, review,