Minggu, 21 Desember 2008

Modis - HDF (Hierarchical Data Format )

MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites.

MODIS data in HDF-EOS format (Hierarchical Data Format - Earth Observing System). Hierarchical Data Format (HDF) is the standard data format for all NASA Earth Observing System (EOS) data products. HDF is a multi-object file format developed by The HDF Group.
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see previous posting about modis tools
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MODIS Tools is helping us to read, extract or subset, convert HDF-EOS data.
1. MODIS Reprojection Tool (MRT)
a software tool for reading data files in HDF-EOS format, specify a geographic subset or band subset as input to processing, perform geographic transformation to a different coordinate system/cartographic projection, write the output to file formats other than HDF-EOS
Platforms : Unix (Sun, SGI), Windows (9x, 2000, NT, XP), and Linux
2. QA Tools
provides links to QA tools developed for science team and user community
Platforms : Unix
3. HDF Tools
The NCSA HDF Home Page - contains links to an array of HDF support tools and information
Platforms : specific to tool selected
4. HDF-EOS Web-Based Subsetter (HEW)
can extract a subset of any grid or swath data file that is in HDF-EOS format Platforms : independent
5. MODIS Swath-to-Grid Toolbox
a set of software tools that reads HDF-EOS files containing MODIS swath data and produces flat binary files containing gridded data in a variety of map projections Platforms : Unix, with a standard C compiler, also requires Perl 5.0 or higher and IDL 5.0 or higher
6. HDF-EOS to GeoTIFF converter (HEG)
converts many EOS products written in HDF-EOS to GeoTIFF, native binary or HDF-EOS Grid, also has re-projection, resampling, subsetting, stitching (mosaicing), and metadata creation capabilities
Platforms : Linux , Macintosh , SGI , Sun, Windows
7. MODIS Land Tile Calculator
converts latitude/longitude decimal degrees to MODIS Tile grid and Line/Sample coordinates and vice-versa
Platforms: online tool

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more informations :
- http://modis.gsfc.nasa.gov/
- http://modis-land.gsfc.nasa.gov/tools.htm
- http://nsidc.org/data/hdfeos/
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Membuka atau mengintip isi dari dataset HDF Modis baik Aqua MODIS maupun Terra MODIS, jika menggunakan software berbayar ENVI 4.x bisa dilakukan dengan melalui fasilitas yang tersedia di ENVI 4.x yaitu:
Basic Tools --> Preprocessing --> Data-Specific Utilities --> View HDF Dataset Attributes
kemudian akan muncul window HDF Selection, tentukan HDF dataset yang akan kita lihat, misal Dataset #5 dari data MODIS MYD02HKM...... :
====================================================================================
Dataset #5: Earth View 250M Aggregated 500M Reflective Solar Bands Scaled Integers
Dims: UINT (2708 x 4060 x 2)

Attribute 5-1: "long_name"
"Earth View 250M Aggregated 500M Reflective Solar Bands Scaled Integers"

Attribute 5-2: "units"
"none"

Attribute 5-3: "valid_range"
0, 32767

Attribute 5-4: "_FillValue"
65535

Attribute 5-5: "band_names"
"1,2"

Attribute 5-6: "radiance_scales"
0.02753444, 0.00927813

Attribute 5-7: "radiance_offsets"
-0.00000000, -0.00000000

Attribute 5-8: "radiance_units"
"Watts/m^2/micrometer/steradian"

Attribute 5-9: "reflectance_scales"
0.00005396, 0.00002950

Attribute 5-10: "reflectance_offsets"
-0.00000000, -0.00000000

Attribute 5-11: "reflectance_units"
"none"

Attribute 5-12: "corrected_counts_scales"
0.12497330, 0.12497330

Attribute 5-13: "corrected_counts_offsets"
-0.00000000, -0.00000000

Attribute 5-14: "corrected_counts_units"
"counts"
====================================================================================
Informasi di atas, seperti radiance dan reflectance baik scale dan offset itulah yang akan digunakan untuk koreksi radiometrik dari data MODIS yang akan kita gunakan.
------------------------------------------------------------------------------------

Selain menggunakan software image processing ENVI 4.x, kita juga bisa menggunakan software-software viewer data HDF, misalnya HDF Explorer
HDF Explorer ini dibuat oleh

Space Research Software, Inc, headquartered in the heart of the Silicon Prairie in Urbana-Champaign, Illinois, is a leading company in HDF related visualization tools. Its flagship product HDF Explorer, is a widely acclaimed software tool that allows an easy browsing of HDF data files.

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HDF Explorer is a data visualization program that reads the HDF, HDF5 and netCDF data file formats. HDF Explorer runs in the Microsoft Windows operating systems. Check this page (http://www.space-research.org/) for version updates, current version is 1.4.025
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HDF (Hierarchical Data Format) is a library and platform independent data format for the storage and exchange of scientific data. HDF is developed and supported by the HDF group
====================================================================================
Membuka atau mengintip isi dari dataset HDF Modis baik Aqua MODIS maupun Terra MODIS, jika menggunakan software HDF Explorer :
====================================================================================
====================================================================================
more information about HDF Explorer : http://www.space-research.org/

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salam rsgis,

Aji Putra Perdana
http://ajiputrap.blogspot.com/

2 komentar:

  1. mas saya masih bingung dengan koreksi radiometrik di modis, terutama pada persamaan emisive ini, Rb = R_scaleb ( SIb – R_offsetsb), di metadata dilihat nilai radiance offsetnya negatif 1577.33972, apakah hasil tersebut bernilai negatif ? bagaimana cara perhitungan sbnrnya ? trimakasih

    BalasHapus
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    BalasHapus