MODIS land products

Preface

The MODIS Land Products collection are generated by NASA and made publicly and freely available by USGS. The products represent NASA global algorithms for terrestrial biophysical parameters such as surface reflection and vegetation.

The products are generated from collated MODIS swath data (level 1) within a window of interest (1 day to 1 year depending on the product), quality controlled and processed, and remapped to a sinusoidal grid from which they are served as tiles. In this manner the products are representative of the window of interest as pixel values may be averages or 'best pixel' within the window. The products are also spatially representative due to the remapping from swath to sinusoidal; that is, users should consider areal trends for their region of interest rather than specific pixel values.

In the Australian context the products represent a good global baseline of terrestrial biophysical data products. They can be used for spatial or temporal context, boundary conditions for modelling, or to compare with tailored algorithms and parameters. Users should read and understand the limitations and dependencies of the NASA global algorithms so that the MODIS land products can be applied and used in the appropriate context.

NASA and USGS product information

The full set of MODIS land products and variants are given at https://lpdaac.usgs.gov/dataset_discovery/modis/modis_products_table. Each product variant has a code, which defines the parameter and the spatial and temporal resolution of the variant.

Each product code link in the table links to a page with:

• A short description
• Details of the bands or variables and quality information in each file
• A DOI and citation (a second DOI and citation are available for the CSIRO and TERN products)
• Links to the User Guide and Algorithm Theoretical Basis Document (ATBD)
• Links to other reference material

Users are encouraged to read the User Guide and ATBD for their products of interest.

Collections

The MODIS land products undergo algorithm enhancements and reprocessing every few years. Major changes to the full suite of products result in an increment of the Collection number. The current Collection number is 6. Collection 5 was stopped on 31 March 2017 (https://lpdaac.usgs.gov/about/news_archive/forward_processing_modis_version_5_land_data_continue_through_march_31_2017).

Sometimes a single product will have a fix or enhancement applied to its algorithm, which may result in a product collection number being incremented at the decimal level, e.g. 5.1 (see MCD12Q1.051) or 5.5 (MOD17A2.055).

Tools and data access

The primary tool for reading the sinusoidal projection tiles is the MODIS Reprojection Tool (MRT), https://lpdaac.usgs.gov/tools/modis_reprojection_tool. This tool will mosaic and reproject tiles for any product. CSIRO use this tool to create the continental mosaics products.

A number of remote sensing image processing software packages can also read and reproject the sinusoidal tiles, such as GDAL and ENVI.

A number of data access options are provided by USGS, https://lpdaac.usgs.gov/data_access. CSIRO use the data access pool with a custom script that compares the USGS holdings with the local copy and batches 'wget' commands to download any new or updated files.

For background information on the sinusoidal projection see:

• Rossow, W. B. and L. Garder (1984) Selection of a map grid for data analysis and archival, Journal of Climate and Applied Meteorology, vol. 23, pp. 1253-1257. http://dx.doi.org/10.1175/1520-0450(1984)023%3C1253:SOAMGF%3E2.0.CO;2
• Masuoka, E., A. Fleig, Robert E. Wolfe and F. Platt (1998) Key characteristics of MODIS Data Products, IEEE Transactions on Geoscience and Remote Sensing, vol. 36, no. 4, pp. 1313-1323. https://doi.org/10.1109/36.701081

Sinusoidal tiles

Source: https://modis-land.gsfc.nasa.gov/MODLAND_grid.html

KMZ: File:Modis sin.kmz (Source: https://modis.ornl.gov/files/modis_sin.kmz)

Quality

Data quality can be characterised in three ways:

1. Validation level of the algorithm
2. Quality of the operational processing inputs and outputs
3. Systematic issues

Validation levels

The validation level or stage of the algorithms is described at https://landval.gsfc.nasa.gov, and summarised here as:

• Stage 1 Product accuracy has been estimated using a small number of independent measurements.
• Stage 2 Product accuracy is estimated over a significant set of locations and time periods.
• Stage 3 Uncertainties are characterized in a statistically rigorous way over multiple locations and time periods representing global conditions.
• Stage 4 Validation results for stage 3 are systematically updated when new product versions are released and as the time-series expands.

The validation stage of each product should be given on the MODIS land products table pages.

Operational processing

Operational processing quality is assessed by https://landweb.nascom.nasa.gov. Select the relevant set from the 'quality' tab, and the relevant product thereafter. Some product pages will be empty. Non-empty product pages will present a table of known processing issues.

Systematic issues

Systematic issues are less well-published and, instead, are identified and investigated from experience. Two issues we are currently aware of are:

1. MOD09 Every 16 days one swath over eastern Australia is mis-collated into the adjacent product window. This comes about from the reference time (and location, e.g. at equator) used to select swath elements for the product relative to the International Data Line.
2. MOD13Q1 Coastline mismatch with other reference data. This is a known problem in the MOD13 processing pipeline and is partly due to using a dynamic, rather than static and thus consistent, land and water mask.

For these and other systematic issues please contact us for more information.

CSIRO processing

collection 5 mosaic and reproject report

Collection 6

csiro, nci and data cube tiles, no more mosaic and reproject (although some transition products) data cube