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MODIS Data at NSIDC
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Terra vs. Aqua
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1. How does MODIS improve upon other optical sensors?
2. What are the limitations of MODIS data?
3. What are the current and planned products at NSIDC?
4. I see the same data product available from Aqua and Terra. Which one should I use?
5. What quality control measures are taken for MODIS products?
6. When and how can I get data?
7. What is the format of the data?
8. Why are MOD10A1 and MOD10A2 Version 4 data in a different grid?
9. What are the different version numbers of MODIS data?
10. I used an earlier version of the data for a research project;
how can I compare the latest data to the data I used before?
11. What other data centers archive and distribute MODIS data?
12. Which products have accompanying browse images?
13. What tools are available for MODIS snow and sea ice products?
14. Is a list of published articles that involved MODIS snow or sea ice data in research available?
15. How can I order MODIS data by tile?
1. How does MODIS improve upon other optical sensors?
MODIS provides global coverage every one to two days in 36 spectral bands. Spatial resolution of the MODIS data varies by band from 250 m to 1000 m. By contrast, the Advanced Very High Resolution Radiometer (AVHRR) sensor has five spectral bands with a spatial resolution of 4 km or 1 km. MODIS data helps scientists understand the Earth as a system, facilitating their ability to predict global climate changes and to differentiate between the impact of human and natural activities on the environment.
2. What are the limitations of MODIS data?
MODIS is an optical sensor, which has inherent limitations in observing sea ice and snow. Unlike a passive-microwave sensor, which can detect microwave energy through clouds, MODIS cannot observe the surface when cloud cover is present. MODIS products, therefore, have cloud masks built into the data arrays to prevent clouds from being interpreted as ice and snow. These cloud masks are continually improved as limitations are documented. Finally, the visible bands of MODIS are only used during the day, when reflectance is the dominant mechanism for detecting ice and snow. The thermal bands are used during both day and night to measure sea ice surface temperature by emittance.
3. What are the current and planned products at NSIDC?
Please see Data Summaries for a list of current products.
4. I see the same data product available from Aqua and Terra. Which one should I use?
Please see Choosing Terra or Aqua MODIS Data.
5. What quality control measures are taken for MODIS products?
The MODIS Land Quality Assessment Web page describes quality control for all MODIS products.
Also, refer to the MODIS Data Product Validation web site for more information.
6. When and how can I get data?
The MODIS snow cover and sea ice products from the Terra satellite are available with observations beginning 24 February 2000, and from the Aqua satellite with observations beginning 4 July 2002. The current lag between time of observation and availability of products is only a few days. The processing and reprocessing schedule for all MODIS data determines the lag time. Please refer to MODIS Product Versions for the processing and reprocessing schedule.
Please see Ordering Data for order options.
7. What is the format of the data?
The data are in Hierarchical Data Format - Earth Observing System (HDF-EOS) format.
HDF is the standard data format for all EOS data products. HDF is a multi-object file format developed by The HDF Group. For more information about the HDF-EOS format, tools for extracting binary and ASCII objects from HDF, and a list of other HDF-EOS resources, please visit NSIDC's HDF-EOS web pages.
8. Why are MOD10A1 and MOD10A2 Version 4 data in a different grid than Version 3?
The MODIS Land Science Team (MODLAND) changed the MOD10A1 and MOD10A2 grids from the Integerized Sinusoidal (ISIN) grid to a standard sinusoidal grid. This change coincided with the Version 4 algorithms, the processing and reprocessing of data into MODIS/Terra Version 4 products, and release of the MODIS/Aqua Version 3 products. The main advantages of the sinusoidal grid are better vendor support and less distortion at the pixel level (no brick-like shifts between rows). The sinusoidal grid also resolves problems with nesting between products with different resolutions.
MODLAND compared the ISIN grid with the sinusoidal grid using the same sphere size, the same upper-left-corner coordinates, and the same cell and tile size. In the line (row) direction, the two grids match exactly. The main difference is in the sample (column) direction. The maximum difference varies for each resolution, with the maximum sample shift of 0.187 of a full 1-km pixel, 0.375 of a 0.5-km pixel, and 0.75 of a 0.25-km pixel. Since the pixels are not exactly 1 km (they are actually 926.62543305 m), the maximum shift is equivalent to 173 m. The calculated Root Mean Square Error (RMS) for the entire globe is 0.36 of a 0.25-km pixel, or about 83 m. This means that at 1 km, the shift is small and can probably be ignored; however, for the finer resolutions, particularly 250 m, the differences are 3/4 of a pixel and should be taken into account when comparing data in the old and new grids.
The following software tools either read data in a sinusoidal projection or convert sinusoidal to other projections:
9. What are the different version numbers of MODIS data?
A version number represents a collection of data with processing refinements for algorithm, instrument and calibration stabilization. This ensures a continuous time series of data with consistent science quality. When a new version becomes available, a small portion of the previous version (see Question 10) remains available to users.
To learn about the different versions of MODIS snow and sea ice products available from NSIDC, refer to our MODIS Product Versions page, or see the MODIS Land Science Team's Validation Status site.
10. I used an earlier version of the data for a research project; how can I compare the latest data to the data I used before?
A portion of data from previous versions is available for comparison. Currently, a sample of Version 3 (V003) data from 29 August 2002 (day 241) through 07 October 2002 (day 280), called the Golden Month, is available for all MODIS/Terra snow and sea ice products. MYD10_L2 and MYD29 MODIS/Aqua Golden Month data (days 241-280) are publicly available through the Warehouse Inventory Search Tool (WIST), SNOWI, and MODIS SNOWI interfaces until 01 October 2005. Other MODIS/Aqua V003 Golden Month products are available by special request by contacting NSIDC User Services.
Please refer to the MODIS Product Versions page for more information.
11. What other data centers archive and distribute MODIS data products?
The NASA Goddard Space Flight Center: MODIS Adaptive Processing System (MODAPS) Services archives and distributes MODIS calibrated channel radiances, and products pertaining to the atmosphere and oceans.
The Land Processes Distributed Active Archive Center (LP DAAC) archives and distributes MODIS products pertaining to land and vegetation.
A complete list of MODIS Terra products available from other DAACs is provided at the following web site: EOS Terra Data Products.
A complete list of MODIS Aqua products available from other DAACs is provided at the following web site: EOS Aqua Data Products.
The Science Computing Facility (SCF) archives and distributes MODIS ocean color and sea surface temperature products. Please visit the xxxx Web site for more information regarding this topic.
12. Which products have accompanying browse images?
The following Version 4 data sets have browse images that accompany each data granule. Beginning with Version 5, all snow and ice products have browse images that accompany each data granule.
In the WIST, you can view browse images by clicking Available under the Image Quicklook column in the resulting granules list. Alternatively, you can view browse images in the FTP directories of the Data Pool.
Also, see Climate Modeling Grid (CMG) Browse Images.
13. What tools are available for MODIS snow and sea ice products?
The free, standalone HDF-EOS to GeoTIFF (HEG) converter (available from the HDF-EOS Tools and Information Center) allows you to geolocate, subset, stitch, and regrid some MODIS/Terra products, as shown in the table below. A future release of the HEG converter will geolocate other MODIS snow and sea ice products, including those from Aqua. If MODIS products are accessed via the Data Pool, the HEG converter is automatically used to perform these operations.
Users also have the option to subset products (as shown in the table below) via the WIST, using the HEW Subsetting Appliance (HSA). Data may be subsetted with the HSA by geographic region using a latitude and longitude bounding box and by desired parameters.
MODIS Products and Tools | ||
|---|---|---|
| Product | Standalone HEG | HSA via WIST |
| MOD10_L2 | X |
X |
| MOD10A1 | X |
X |
| MOD10A2 | X |
X |
| MOD10C1 | X |
X |
| MOD10C2 | X |
X |
| MYD10_L2 | X |
|
| MYD10A1 | X |
|
| MYD10A2 | X |
|
| MYD10C1 | X |
X |
| MYD10C2 | X |
X |
| MOD29 | X |
X |
| MOD29P1D | X |
X |
| MOD29P1N | X |
X |
| MOD29E1D | ||
| MYD29 | X |
|
| MYD29P1D | X |
|
| MYD29E1D | ||
The free MODIS reprojection tool transforms all MODIS/Terra and MODIS/Aqua Level-3 gridded snow and ice products from integerized sinusoidal (ISIN) and sinusoidal (SIN) projections to user-specified projections. Use the MODIS Swath Reprojection Tool to transform MODIS/Terra and MODIS/Aqua Level-2 snow and ice products from HDF-EOS swath format to a uniformly gridded image that is geographically referenced according to user-specified projection and resampling parameters.
Also, see Geolocating HDF-EOS Data for more details.
14. Is a list of published articles that involved MODIS snow or sea ice data in research available?
Yes, the Research page lists citations of published research.
15. How can I order MODIS Data by Tile?
You can order MODIS data by tile using two different methods:
