Rabu, 21 Januari 2009

MODIS (Aqua/Terra)-Image Processing (1)

MODIS (Aqua/Terra)-Image Processing (1)

this is just a little bit sharing... :)

you may or have been read :
http://ajiputrap.blogspot.com/search/label/Aqua
http://ajiputrap.blogspot.com/search/label/Aqua%2FTerra%20MODIS
http://ajiputrap.blogspot.com/search/label/MODIS

After we download MODIS (Aqua/Terra) Level 1B Radiance Calibrated (1KM, 500m and 250m, opr you just download 1KM only (its already consist of 250m and 500m that aggregated to 1km) and Level 1A Geolocation (for extracting LAND SEA MASK).

The next step is to open HDF MODIS data in Image Processing Software, such as ENVI...
in this post i would like to share about open HDF MODIS DATA, View HDF DATASETS and other steps in image processing using software ENVI 4.x.

1. In ENVI 4.x u may open HDF MODIS DATA through two ways:
a. Open HDF MODIS data from:
File -> Open External Files -> General Format -> HDF

U will see HDF Dataset Selection, and then choose Datasets (that to be opened)
Click OK
Choose BSQ and click OK (repeated until 4 times, depend on number of dataset opened)

b. Or u may open directly from
File -> Open Image File

Will open all modis data from MYD021KM: Reflectance and Radiance Bands (1- 19 and 26) also Emissive Bands (20-25 and 27-36)

Your MODIS DATA will opened in ENVI 4.x

2. View HDF Datasets of MODIS
from ENVI 4.x main menu..choose Basic Tools->Preprocessing->Data Specific Utilities -> View HDF Datasets Attributes
and then choose your MODIS DATA...
u can read my previous posting :
http://ajiputrap.blogspot.com/2008/12/modis-hdf-hierarchical-data-format.html

3. Radiometric Correction
Radiometric Correction in ENVI use Band Math (ENVI main menu, choose Basic Tool -> Band Math)

Radiance bands calculated using this formula :
Rb = R_scaleb ( SIb – R_offsetsb)
where :
Rb = Radiance of band-b
R_Scaleb = Radiance scale of band-b
SIb = Sign Integer of band-b
R_offset¬sb = Radiance offsets of band-b

Radiance value of sensor zenith calculated using this formula :
Rz = R_scalez * iz * pi/180
dimana :
Rz = Radiance value of sensor zenith
R_scalez = Radiance scale of sensor zenith
iz = Sensor zenith


Reflectance Bands calculated for visible and thermal infrared (1 – 19 and 26 bands) with this formula:

Refb = Ref_Scaleb * (Bb - Ref_offsetsb)

where: Refb = Reflectance of band- b
Ref_Scaleb = Reflectance scale
Bb = Band -b
Ref_offsetsb = Reflectance offset band- b

4. applied formula or algorithm (for Sea Surface Temperature or Chlorophyll-a)

MODIS can help us to detecting Chlorophyll-a (Chlor-a) with formula or algorithm from Carder et al. :

Chlor-a=(10^(0.2818-(2.783*alog10(B10/B12))+(1.863*((alog10(B10/B12))^2))-
(2.387*((alog10(B10/B12))^3))))

where : B10 = Reflecance of Band 10
B12 = Reflecance of Band 12
- above is the formula of Chlor-a in Band Math of ENVI.

Aqua MODIS image processing for sea surface temperature using two bands : band 31 and band 32 (that have processed for corrected radiance value).
We need to convert radiance value both bands (31 and 32) to Brightness Value using “Planck”:

Tb = c2/(Vi * ln (c1/(Vi5 * radiance) + 1))
where Tb = Brightness Value (K),
c1 = Constanta radiance (1.1910659x108 [W m -2sr-1 (µm-1 )-4 ])
c2 = Constanta radiance (1.438833 x 104 [K µm])
Vi = central wavelength

You can use band math ENVI 4.x and put this formula:
(1.438833*10000)/(11.0263*(alog((1.1910659*100000000)/(11.0263^5*b31))/1))
where :
b31 = band 31
to determine or get information of Sea Surface Temperature you may use this algorithm from Brown and Minnet :
SPL =
1.152+0.96*(B1-273)+0.151*(B1-B2)*(B3-273)+2.021*(B1-B2)*(1/COS(B4)-1)

where
B1 = Brightness Value of band 31
B2 = Brightness Value of band 32
B3 = Brightness Value of band 20
B4 = Radiance Value of sensor zenith



=========
Regards,

Aji Putra Perdana

5 komentar:

  1. Salam, gembira rasanya kerana dapat membaca dan memahami ilmu yang dikongsi bersama oleh saudara. Terima kasih.

    Tapi saya dapati terdapat kesilapan pada formula bagi menukarkan radiance kepada brightness temperature menggunakan band math ENVI iaitu:

    (1.438833*10000)/(11.0263*(alog((1.1910659*100000000)/(11.0263^5*b31))/1))

    Lihat dihujungnya ialah /1 dan bukannya +1.
    Berdasarkan formula asalnya ialah:

    Tb = c2/(Vi * ln (c1/(Vi5 * radiance) + 1))

    Saya begitu gembira sekali apabila copy dan menggunakan formula bagi band math tersebut kerana saya dapat hasilnya. Namun setelah meneliti semula formula, saya dapati ianya salah. Saya telah cuba menggunakannya berdasarkan formula(plank) yang asal, namun hasilnya tidak tepat.

    Bolehkah saudara membantu bagi mengatasi masalah ini?. Saya amat memerlukan pertolongan.
    Sekian

    BalasHapus
  2. mas aji saya mau tanya, saat ini saya sedang mengambil tugas akhir mengenai perhitungan suhu permukaan laut menggunakan citra aqua modis level 1b dengan software envi..
    lah ak masi bingung buat nyari brightness temperature nya mas,,ak ngitung splnya pake matlab..
    gimana dunt mas ??tlg segera dijawab ya mas..(bingung mode on)
    thanks mas ^^

    BalasHapus
  3. mas aji, saya ingin bertanya, saya sedang mengambil tugas akhir mengenai suhu permukaan laut menggunakan citra aqua modis level 1b, saya bingung nyari rums temperature brightness nya,mungkin mas aji punya literaturnya,,
    kebetulan saya menggunakan envi,saya sangat mmerlukan jawabanbya mas,
    terimakasih

    BalasHapus
  4. coba baca2x buku image processing atau remote sensing yang didalamnya memuat mengenai remote sensing untuk sensor thermal

    BalasHapus
  5. mas,mau tanya lagi,,sign integer of band itu apa ??
    bukan digital number kah ??
    setelah ta coba ko warna jadi hitam dan nilainya NaN (bukannya itu berarti ta terdefinisi ya ?? >_<)
    mohon dijawab ya mas ?? udah baca tapi juga belum nemu...

    BalasHapus