Dear All,
I am analyzing MODIS EVI time sereis for 2004-2010. Preprocessing 
included: reprojecting to WGS84 and export EVI to Geotiff (along with 
blue reflectance and view zenith angel). Then I filtered out cloudy  
(blue reflectance more than 10%) and off-nadir (angel > 32.5) pixels. 
Now, I am trying to interpolate the missing values, so I tried the 
following:

#first linear interpolation
#convert Tiffs to points (rasterToPoints)
 > r01 <- raster("2004001_evi_filtered.tif")/10000
 >r01_p <- rasterToPoints(r89,fun=function(x){x>-0.9999})
#Then bind EVI columns, along with X,Y coordinates:
 >evi <- rbind ( EVI2004_1_1=r01_p[,3], EVI2004_1_17=r02_p[,3], 
.......,X= r153_p[,1], Y= r153_p[,2] )
#set 0 values to NA
 >evi[evi == 0] <- NA
 >evi=interpNA(evi, method = "linear")

then I transposed the evi to plot it with plotKML


Now I am trying to use alternative interpolation method for better 
results. MODIS package offer whittaker.raster filtering algorithm

 >evi2 = preStack(pattern = "*.tif", path = "path/to/file")
 >timeInfo <- orgTime(evi2,nDays=16,begin="2004001",end="2010241",pillow=40)
 >evi2 <- preStack(files=evi2,timeInfo=timeInfo)
 >beginCluster(type="SOCK",exclude="MODIS") # See: ?beginCluster
 >system.time(whittaker.raster(evi2,timeInfo=timeInfo,lambda=1000))

My questions are:
1. Is the modified whittaker filter functionreally suitable for 
interpolation in my case?
2. How to destack the resulting GeoTiffs (from whittaker.raster)? I want 
to plot the series using plotKML to visualize the results
3. Some researchers suggested wavelet transformation to smooth the data, 
is that comprable to whittaker function?


Thank you in advance

Mohammad

p.s. I am new to r and would appreciate simple explanations!




-- 
PhD Candidate
Institute of Crop Science and Resource Protection
Crop Science Research Group
Katzenburgweg 5 - 53115 Bonn - Germany
Tel.: +49 (0) 228 73 2030     Fax: +49 (0) 228 73 2870
abdelrazek@uni-bonn.de        http://www.lap.uni-bonn.de


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