i.modis - GRASS GIS manual

NAME

i.modis - Toolset for download and processing of MODIS products using pyModis.

The i.modis suite is a toolset to import MODIS (Moderate Resolution Imaging Spectroradiometer, flown on the two NASA spacecrafts Terra and Aqua) satellite data into GRASS GIS. It uses the pyModis library and additionally either the GDAL library or the MODIS Reprojection Tool (MRT) software to convert, mosaic and process MODIS data.

The i.modis suite requires the pyModis library and either the GDAL or MRT software to be installed.

The i.modis suite offers two modules as interface to MODIS data. Each module is dedicated to a specific operation. The module i.modis.download is used to download MODIS HDF products from NASA servers. These files can then be imported with i.modis.import which supports import of Level 3 MODIS products as a single image or as a mosaic into GRASS GIS.

Subsequently, the user can create a temporal dataset using t.create and, register the maps with t.register. NOTE: In order to work with the temporal framework of GRASS GIS the flag w must be set during the import with i.modis.import.

The user can choose from several MODIS products, distributed as single or multiple tiles and also ranges of observation days retrieving data from the related NASA servers. The suite imports Level 3 (georeferenced) products either as single images or as mosaics for each date.

Supported MODIS products

These products are currently supported:

MODIS Surface Reflectance

Surface spectral reflectance daily 1 km and 500 m (Terra/Aqua): Bands 1 through 7 corrected for atmospheric conditions such as gasses, aerosols, and Rayleigh scattering in Sinusoidal projection daily. Provided along with the 500 meter (m) surface reflectance, observation, and quality bands are a set of ten 1 kilometer observation bands and geolocation flags. The reflectance layers from MOD09GA and MYD09GA are used as the source data for many of the MODIS land products (related MOD09GA and MYD09GA product pages).
Surface spectral reflectance eight day 500 m (Terra/Aqua): Bands 1 through 7 corrected for atmospheric conditions such as gasses, aerosols, and Rayleigh scattering in Sinusoidal projection during an 8-day period. Along with the seven 500 meter (m) reflectance bands are two quality layers and four observation bands. For each pixel, a value is selected from all the acquisitions within the 8-day composite period. The criteria for the pixel choice include cloud and solar zenith. When several acquisitions meet the criteria, the pixel with the minimum channel 3 (blue) value is used (related MOD09A1 and MYD09A1 product pages).

MODIS LST - Land Surface Temperature

Land Surface Temperature daily 1 km (Terra/Aqua): product provides per-pixel temperature and emissivity values in a sequence of swath-based to grid-based global products in Sinusoidal projection. The MODIS/Terra-Aqua LST/E Daily L3 Global 1 km Grid product (MOD11A1/MYD11A1), is tile-based and gridded in the Sinusoidal projection, and produced daily at 1 km spatial resolution (related MOD11A1 and MYD11A1 product pages).
Land Surface Temperature eight day 1 km (Terra/Aqua): data are composed from the daily 1-kilometer LST product (MOD11A1/MYD11A1) and stored on a 1-km Sinusoidal grid as the average values of clear-sky LSTs during an 8-day period.
MOD11A2/MYD11A2 is comprised of daytime and nighttime LSTs, quality assessment, observation times, view angles, bits of clear sky days and nights, and emissivities estimated in Bands 31 and 32 from land cover types (related MOD11A2 and MYD11A2 product pages).
Land Surface Temperature eight day ~6 km (Terra/Aqua): products provide per-pixel temperature and emissivity values in a sequence of swath-based to grid-based global products. The MODIS/Terra-Aqua LST/E Daily L3 Global 6 km Grid (Short name: MOD11B1/MYD11B1), is tile-based and gridded in the Sinusoidal projection, and produced daily at 5600m spatial resolution (related MOD11B1 and MYD11B1 product pages).
Land Surface Temperature monthly ~6 km (Terra/Aqua): products provide per-pixel temperature and emissivity values in a sequence of swath-based to grid-based global products with a pixel size of 5,600 meters. Each LST&E pixel value in the MOD11B3 is a simple average of all the corresponding values from the MOD11B1 collected during the month period. Each MOD11B3 granule consists of 19 layers including daytime and nighttime layers for LSTs, quality control assessments, observation times, view zenith angles, and number of clear sky observations along with percentage of land in the tile and emissivities from bands 20, 22, 23, 29, 31, and 32. Unique to the MOD11B products are additional day and night LST layers generated from band 31 of the corresponding 1 km MOD11_L2 swath product aggregated to the 6 km grid (related MOD11B3 and MYD11B3 product pages).

MODIS VI - Vegetation Indices

VI sixteen days 250 m (Terra/Aqua): Global MOD13Q1/MYD13Q1 MODIS vegetation indices are designed to provide consistent spatial and temporal comparisons of vegetation. conditions. Blue, red, and near-infrared reflectances, centered at 469-nanometers, 645-nanometers, and 858-nanometers, respectively, are used to determine the MODIS daily vegetation indices.
The MODIS Normalized Difference Vegetation Index (NDVI) complements NOAA's Advanced Very High Resolution Radiometer (AVHRR) NDVI products and provides continuity for time series historical applications. MODIS also includes a new Enhanced Vegetation Index (EVI) that minimizes canopy background variations and maintains sensitivity over dense vegetation conditions. The EVI also uses the blue band to remove residual atmosphere contamination caused by smoke and sub-pixel thin cloud clouds. The MODIS NDVI and EVI products are computed from atmospherically corrected bi-directional surface reflectances that have been masked for water, clouds, heavy aerosols, and cloud shadows. Global MOD13Q1/MYD13Q1 data are provided every 16 days at 250-meter spatial resolution as a gridded level-3 product in the Sinusoidal projection. Lacking a 250m blue band, the EVI algorithm uses the 500m blue band to correct for residual atmospheric effects, with negligible spatial artifacts (related MOD13Q1 and MYD13Q1 product pages).
VI sixteen days 500 m (Terra/Aqua): Global MOD13A1/MYD13A1 MODIS vegetation indices are designed to provide consistent spatial and temporal comparisons of vegetation conditions. Blue, red, and near-infrared reflectances, centered at 469-nanometers, 645-nanometers, and 858-nanometers, respectively, are used to determine the MODIS daily vegetation indices.
The MODIS Normalized Difference Vegetation Index (NDVI) complements NOAA's Advanced Very High Resolution Radiometer (AVHRR) NDVI products provide continuity for time series historical applications. MODIS also includes a new Enhanced Vegetation Index (EVI) that minimizes canopy background variations and maintains sensitivity over dense vegetation conditions. The EVI also uses the blue band to remove residual atmosphere contamination caused by smoke and sub-pixel thin cloud clouds. The MODIS NDVI and EVI products are computed from atmospherically corrected bi-directional surface reflectances that have been masked for water, clouds, heavy aerosols, and cloud shadows.
Global MOD13A1/MYD13A1 data are provided every 16 days at 500-meter spatial resolution as a gridded level-3 product in the Sinusoidal projection. Vegetation indices are used for global monitoring of vegetation conditions and are used in products displaying land cover and land cover changes. These data may be used as input for modeling global biogeochemical and hydrologic processes and global and regional climate. These data also may be used for characterizing land surface biophysical properties and processes, including primary production and land cover conversion (related MOD13A1 and MYD13A1 product pages).
VI sixteen days 250 m (Terra/Aqua): The MOD13Q1 product provides two primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI) which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The algorithm chooses the best available pixel value from all the acquisitions from the 16 day period. The criteria used is low clouds, low view angle, and the highest NDVI/EVI value. Along with the vegetation layers and the two quality layers, the HDF file will have MODIS reflectance bands 1 (red), 2 (near-infrared), 3 (blue), and 7 (mid-infrared), as well as four observation layers (related MOD13Q1 and MYD13Q1 product pages).
VI sixteen days 1 km (Terra/Aqua): The MOD13A2 product provides a Vegetation Index (VI) value at a per pixel basis. There are 2 primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI) which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The data are provided at 1000 m resolution as a gridded level-3 product in the Sinusoidal projection (related MOD13A2 and MYD13A2 product pages).
VI monthly 1 km (Terra/Aqua): The MOD13A3 product provides a Vegetation Index (VI) value at a per pixel basis. There are 2 primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI) which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The data are provided at 1000 m resolution as a gridded level-3 product in the Sinusoidal projection. Provided along with the vegetation layers and the two quality assurance (QA) layers are reflectance bands 1 (red), 2 (near-infrared), 3 (blue), and 7 (mid-infrared), as well as three observation layers (related MOD13A3 and MYD13A3 product pages).
VI sixteen days Global 0.05Deg CMG (Terra/Aqua): The MOD13C1 product provides a Vegetation Index (VI) value at a per pixel basis. There are 2 primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI) which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The Climate Modeling Grid (CMG) consists 3600 rows and 7200 columns of 5600 m pixels and is provided as a global latitude/longitude grid (related MOD13C1 and MYD13C1 product pages).
VI monthly Global 0.05Deg CMG (Terra/Aqua): The MOD13C2 product provides a Vegetation Index (VI) value at a per pixel basis. There are 2 primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI) which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The Climate Modeling Grid (CMG) consists 3600 rows and 7200 columns of 5600 m pixels and is provided as a global latitude/longitude grid (related MOD13C2 and MYD13C2 product pages).

MODIS AOD - Aerosol Optical Depth

Aerosol optical depth daily 1 km (Terra+Aqua): MCD19A2 is the short name for the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm-based Level-2 gridded (L2G) aerosol optical thickness over land surfaces product. This product is derived using both Terra and Aqua MODIS inputs, and produced daily at 1 km pixel resolution in a Sinusoidal projection. MCD19A2 has achieved Stage-3 validation, and each Hierarchical Data Format 4 (HDF4) file contains two data groups with the following Science Data Set parameters: Grid 1km: 1. Aerosol Optical Depth at 047 micron / 2. Aerosol Optical Depth at 055 micron / 3. AOD Uncertainty at 047 micron / 4. Fine-Mode Fraction for Ocean / 5. Column Water Vapor in cm liquid water / 6. AOD QA / 7. AOD Model (Regional background model used) / 8. Injection Height (Smoke injection height over local surface height) Grid 5km: 9. Cosine of Solar Zenith Angle / 10. Cosine of View Zenith Angle / 11. Relative Azimuth Angle / 12. Scattering Angle / 13. Glint Angle. See the validation webpage for details on the validation and validation definitions (related MCD19A2 product pages).

MODIS Snow

Snow daily 500 m (Terra/Aqua): MOD10A1 and MYD10A1 are tiles of daily snow cover at 500 m spatial resolution. The daily observation selected from multiple observations in a MOD10A1 (or MYD10A1) cell is the observation acquired nearest nadir and having the greatest coverage of the grid cell. The daily MOD10A1 and MYD10A1 snow products are tiles of data gridded in the sinusoidal projection. Tiles are approximately 1200 x 1200 km in area. A single scientific data set (SDS) of snow cover and a single SDS of QA data along with local and global attributes comprise the data product file. The daily level 3 snow product is the result of selecting an observation from the multiple observations mapped to a cell of the MOD10_L2G (or MYD10_L2G) product. See the validation webpage for details on the validation and validation definitions (related MOD10A1 and MYD10A1 product pages).
Snow eight days 500 m (Terra/Aqua): The MOD10A2 and MYD10A2 products are composites of eight days of snow maps in the sinusoidal grid. An eight-day compositing period was chosen because that is the exact ground track repeat period of the Terra and Aqua platforms. Snow cover over eight days is mapped as maximum snow extent in one SDS and as a chronology of observations in the other SDS. Eight-day periods begin on the first day of the year and extend into the next year. The product can be produced with two to eight days of input. There may not always be eight days of input, because of various reasons, so the user should check the attributes to determine on what days observations were obtained. See the validation webpage for details on the validation and validation definitions (related MOD10A2 and MYD10A2 product pages).

MODIS Land Water Mask

Land Water Mask 250 m (Terra): The Version 6 data product provides a global map of surface water at 250 meter (m) spatial resolution. The data are available annually from 2000 to 2015. MOD44W Version 6 is derived using a decision tree classifier trained with MODIS data and validated with the Version 5 MOD44W data product. A series of masks are applied to address known issues caused by terrain shadow, burn scars, cloudiness, or ice cover in oceans. A primary improvement in Version 6 is the generation of time series data rather than a simple static representation of water, given that water bodies fluctuate in size and location over time due to both natural and anthropogenic causes. Provided in each MOD44W Version 6 Hierarchical Data Format 4 (HDF4) file are layers for land, water, no data, and an associated per pixel quality assurance (QA) layer that provides users with information on the determination of water (related MOD44W product page).