8/10/10 1 ndvi calculation of rs data
TRANSCRIPT
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NDVI Calculation of RS Data
November Seminar- 28 /11/06
Shamim Akhter PhD Student
AIDA Lab Department of Information Processing
Tokyo Institute of Technology, Japan
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Aster reflectance image ASTER stands for Advanced Space borne
Thermal Emission and Reflection Radiometer ASTER started monitoring global environment
changes in March 2000 and it provides image. Sensor on-board Terra is having 14 spectral
bands ranging from 15 to 90 m spatial resolution.
A fifteenth band is a backward view of the NIR (15 x 15 m in the 0.76 to 0.86 μm) for stereoscopic imaging.
L1B image can be acquired by ftppull from the EROS Data Center Internet website and costs $50 per image.
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Table 1: Aster Sensor Characteristics
SensorProduct
Sub-System Number of bands Spectral range (μm)
Spatial resolution (m)
Aster L1B VNIR 3 (+ 1 backward) 0.52 up to 0.86 15x15
SWIR 6 1.60 up to 2.43 30x30
TIR 5 8.125 up to 11.65 90x90
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Modis 8 days reflectance MODIS (Moderate Resolution Imaging
Spectroradiometer) is the key instrument aboard the Terra (EOS AM-1) satellite.
MODIS started functioning in March 2000. Terra MODIS is viewing the entire Earth's surface every
to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths.
Modis sensor on TERRA platform has a spectral resolution featuring 36 bands ranging from 250 to 1000 meters spatial resolution.
Acquisition of surface reflectance image products (MOD09A1) can be done freely through the Eros Data Center Internet web site using ftppull protocol. Extraction of the binary file can be performed for the necessary bands. The date of the satellite overpass for this image of central Thailand was 13th of March 2000.
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Table 2: MOD09_L3_8-Day Characteristic
Product Sub-Systems Number of bands Spectral range (μm) Spatial resolution (m)
ModisMOD09A1
VNIR 2 0.62 up to 0.876 500x500
SWIR 5 0.459 up to 2.155 500x500
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RS Image Handling Libraries The remote sensing imagery is generally a common type of
binary image format (BIL, BSQ, TIFF, etc) that is not compressed since the digital numbers are of physical meanings to remote sensing scientists.
A particularity of the remote sensing data is that it is georeferenced. Meaning that each pixel of the images are having a unique location on the surface of the Earth.
Honda (1995) developed a C language based image handling library available on the internet (http://www.star.ait.ac.th/~honda/textbooks/advdip/imagelib.zip) and released under the GNU Public License (www.fsf.org).
It has been used for these experiments. It can handle jpeg, tiff, ENVI and ER Mapper image formats. Currently having georeferencing support, the ENVI format is the one used in this processing.
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NDVI Calculationvoid NDVI_CALC(int h, int w, u_char *nir, u_char *red, u_char
*ndvi){
int i,j;double wk;for (i=0; i<h; i++ ){
for(j=0; j<w; j++ ){ wk = (double) ( nir[i*h+j] - red[i*h+j] ) / (double)
( nir[i*h+j] + red[i*h+j] ); ndvi[i*h+j] = wk *100.0 + 100.0; } }}
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MPI Versions
The NDVI program is distributed with two methodologies and successfully implemented in Cluster computers by using MPI Libraries. Distributed each pixel. Distributed each row.
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Modis processing time (by rowmethod) for different sets of
operations
0
120
240
360
480
600
720
840
0 1 2 3 4 5 6 7 8Number of nodes used
Tim
e (s
)
5
500
1000
1500
2500
Aster processing time (by rowmethod) for different sets of
operations
0
60
120
180
240
300
360
420
0 1 2 3 4 5 6 7 8Number of nodes
Tim
e (s
)
5
5000
25000
It is observed that there is a point of convergence of all curves for a given image with an increasing number of operations applied. Aster image experiment at 25000 operations shows a minimum time processing at about 40 seconds with 7 nodes. While the number of operations sets tested in the case of Aster image is not enough to conclude more with certainty. Modis image provides some insights of additional operational limits. The Modis convergence time of processing is found to be about 150 seconds with the maximum node number. From the same graph, it seems that above 1500 operations is the minimum complexity of pixel processing that this Modis image would benefit from being processed in a distributed manner.
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Parallel Methodology
MSVI
………
NDVI
RVI
Server 1
MSVI
………
NDVI
RVI
MSVI
………
NDVI
RVI
Server 2
Server n
Client Side
Server Side
Row wise distribution is preferred because of single pixel executions timing is only less
amount of time
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Difference with r.vi
r.vi is a full package. r.vi is run able in GRASS environment. Where as this NDVI calculation program is
simple C code.
r.vi extracts a pixel by pixel information and there after distributed whole row at a time.
Where this C program extracts all pixels information (Dr.Honda`s C library) and puts them in 2D arrays. Then the array is going to process.
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Grid Version
NDVI_ALL folder…..
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December Task
Experiment on the running time for all three versions.
Compare the timing.. Sensei`S requirements…… I will present Introduction about
Remote Sensing …