8/10/10 1 NDVI Calculation of RS Data


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8/10/10 1 NDVI Calculation of RS Data

  1. 1. 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
  2. 2. Aster reflectance image <ul><li>ASTER stands for Advanced Space borne Thermal Emission and Reflection Radiometer </li></ul><ul><li>ASTER started monitoring global environment changes in March 2000 and it provides image. </li></ul><ul><li>Sensor on-board Terra is having 14 spectral bands ranging from 15 to 90 m spatial resolution. </li></ul><ul><li>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. </li></ul><ul><li>L1B image can be acquired by ftppull from the EROS Data Center Internet website and costs $50 per image. </li></ul>
  3. 3. Table 1: Aster Sensor Characteristics 90x90 8.125 up to 11.65 5 TIR 30x30 1.60 up to 2.43 6 SWIR 15x15 0.52 up to 0.86 3 (+ 1 backward) VNIR Aster L1B Spatial resolution (m) Spectral range (μm) Number of bands Sub-System Sensor Product
  4. 4. Modis 8 days reflectance <ul><li>MODIS (Moderate Resolution Imaging Spectroradiometer) is the key instrument aboard the Terra (EOS AM-1) satellite. </li></ul><ul><li>MODIS started functioning in March 2000. </li></ul><ul><li>Terra MODIS is viewing the entire Earth's surface every to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths. </li></ul><ul><li>Modis sensor on TERRA platform has a spectral resolution featuring 36 bands ranging from 250 to 1000 meters spatial resolution. </li></ul><ul><li>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. </li></ul>
  5. 5. Table 2: MOD09_L3_8-Day Characteristic 500x500 0.459 up to 2.155 5 SWIR 500x500 0.62 up to 0.876 2 VNIR Modis MOD09 A1 Spatial resolution (m) Spectral range (μm) Number of bands Sub-Systems Product
  6. 6. RS Image Handling Libraries <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>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). </li></ul><ul><li>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. </li></ul>
  7. 7. NDVI Calculation <ul><li>void NDVI_CALC(int h, int w, u_char *nir, u_char *red, u_char *ndvi) </li></ul><ul><li>{ </li></ul><ul><li>int i,j; </li></ul><ul><li>double wk; </li></ul><ul><li>for (i=0; i<h; i++ ){ </li></ul><ul><li>for(j=0; j<w; j++ ){ </li></ul><ul><li>wk = (double) ( nir[i*h+j] - red[i*h+j] ) / (double)( nir[i*h+j] + red[i*h+j] ); </li></ul><ul><li>ndvi[i*h+j] = wk *100.0 + 100.0; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>
  8. 8. MPI Versions <ul><li>The NDVI program is distributed with two methodologies and successfully implemented in Cluster computers by using MPI Libraries. </li></ul><ul><ul><li>Distributed each pixel. </li></ul></ul><ul><ul><li>Distributed each row. </li></ul></ul>
  9. 9. <ul><li>It is observed that there is a point of convergence of all curves for a given image with an increasing number of operations applied. </li></ul><ul><li>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. </li></ul><ul><li>Modis image provides some insights of additional operational limits. </li></ul><ul><li>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. </li></ul>
  10. 10. Parallel Methodology Server 1 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 MSVI ……… NDVI RVI MSVI ……… NDVI RVI MSVI ……… NDVI RVI
  11. 11. Difference with r.vi <ul><li>r.vi is a full package. </li></ul><ul><li>r.vi is run able in GRASS environment. </li></ul><ul><li>Where as this NDVI calculation program is simple C code. </li></ul><ul><li>r.vi extracts a pixel by pixel information and there after distributed whole row at a time. </li></ul><ul><li>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. </li></ul>
  12. 12. Grid Version <ul><li>NDVI_ALL folder….. </li></ul>
  13. 13. December Task <ul><li>Experiment on the running time for all three versions. </li></ul><ul><li>Compare the timing.. </li></ul><ul><li>Sensei`S requirements…… </li></ul><ul><li>I will present Introduction about Remote Sensing … </li></ul>