Contents:INTRODUCTIONFile Format of LST ProductsSequence of LST Products |
IntroductionThe MODIS LST products are created as a sequence of products beginning with a swath (scene) and progressing, through spatial and temporal transformations, to daily and eight-day global gridded products. The algorithms and data content of these LST products are briefly described in this guide with the purpose of providing a user with sufficient information about the content and structure of the data files to enable the user to access and use the data. Overviews of the file format and sequence of MODIS LST products are given first. Descriptions of each algorithm and product content are given in following sections. World Wide Web sites and documents related to the MODIS LST products are listed in the last two sections.File Format of LST ProductsThe MODIS LST products are archived in Hierarchical Data Format - Earth Observing System (HDF-EOS) format files. HDF, developed by the NSCA, is the standard archive format for EOS Data Information System (EOSDIS) products. The LST product files contain global attributes (metadata) and scientific data sets (SDSs) (arrays) with local attributes. Unique in HDF-EOS data files is the use of HDF features to create point, swath, and grid structures to support geolocation of data. These structures (Vgroups and Vdata) provide geolocation relationships between data in an SDS and geographic coordinates (latitude and longitude or map projections) to support mapping the data. Attributes (metadata), global and local, provide various information about the data. Users unfamiliar with HDF and HDF-EOS formats may wish to consult Web sites listed in the Related Web Sites section for more information.LST data product files contain three EOS Data Information System (EOSDIS) Core System (ECS) global attributes, which are also referred to as metadata by ECS. These ECS global attributes (CoreMetadata.0, ArchiveMetadata.0 and StructMetadata.0) contain information relevant to production, archiving, user services, geolocation and analysis of data. The ECS global attributes are written in parameter value language (PVL) and are stored as a character string. Metadata and values are stored as objects within the PVL string. Results of the LST algorithms are stored as SDSs with local attributes. Local attributes include summary statistics and other information about the data in an SDS or a key to data values. Detailed descriptions of each LST product are given in following sections. Products may also contain product specific attributes (PSAs) defined by the product developers as part of the ECS CoreMetadata.0 attribute. Geolocation and gridding relationships between HDF-EOS point, swath, and grid structures and the data are contained in the ECS global attribute, StructuralMetadata.0. A separate file containing metadata will accompany data products ordered from a DAAC. That metadata file will have a .met extension and is written in PVL. The .met file contains some of the same metadata as in the product file but also has other information regarding archiving and user support services as well as some post production quality assurance (QA) information relevant to the product file ordered. The post production QA metadata may or may not be present depending on whether or not the data file has been investigated. The .met file should be examined to determine if post production QA has been applied to the product file. (The Quality Assurance sections of this guide provide information on post production QA.) The data products were generated in the science data production system using the HDF-EOS toolkit, Science Data Processing (SDP) Toolkit, HDF API and the C programming language. Various software packages, commercial and public domain, are capable of accessing the HDF-EOS files. Sequence of LST ProductsLST data products are produced as a series of seven products. The sequence begins as a swath (scene) at a nominal pixel spatial resolution of 1km at nadir and a nominal swath coverage of 2030 or 2040 lines (along track, about five minutes of MODIS scans) by 1354 pixels per line. A summarized listing of the sequence of products is given in Table 1. Products in EOSDIS are labeled as Earth Science Data Type (ESDT), the ESDT label "shortname" is used to identify the LST data products. Except for the initial daily LST products, MOD11_L2, MOD11A1, and MOD11B1, each LST product in the sequence is built from the previous LST products. These LST products are identified, in part, by product levels in EOSDIS which indicate what spatial and temporal processing has been applied to the data.Data product levels briefly described: Level 1B (L1B) is a swath (scene) of MODIS data geolocated to latitude and longitude centers of 1 km resolution pixels. A level 2 (L2) product is a geophysical product that remains in latitude and longitude orientation; it has not been temporally or spatially manipulated. A level 3 (L3) product is a geophysical product that has been temporally and or spatially manipulated, and is usually in a gridded map projection format referred to as tiles. Each tile is a piece, e.g., about 1113km by 1113km in 1200 rows by 1200 columns, of a map projection. Brief descriptions of the LST data products are given here to give perspective to the sequence. Expanded descriptions of the LST products are given in following sections. The first product, MOD11_L2, is a LST product at 1km spatial resolution for a swath. This product is the result of the generalized split-window LST algorithm (Wan and Dozier, 1996). Geolocation data (latitude and longitude) at 5 km resolution is also stored in the product. The second product, MOD11A1, is a tile of daily LST product at 1km spatial resolution. It is generated by mapping the pixels from the MOD11_L2 products for a day to the Earth locations on the integerized sinusoidal or sinusoidal projection. The third product, MOD11B1, is a tile of daily LST and emissivities at 5km spatial resolution. It is generated by the day/night LST algorithm (Wan and Li, 1997). The fourth product, MOD11A2, is an eight-day LST product by averaging from two to eight days of the MOD11A1 product. The fifth product, MOD11C1, is a daily global LST product in a geographic projection. It is created by assembling the MOD11B1 daily tiles together and resampling the 5km cell observations to the 0.05° spatial resolution of the Climate Modeling Grid (CMG) cells. The sixth product, MOD11C2, is an eight-day composite of LST at the same resolution as MOD11C1. The seventh product, MOD11C3, is a monthly composite of LST at the same resolution as MOD11C2. The day/night LST algorithm needs a pair of daytime and nighttime L1B data in seven TIR bands, atmospheric temperature and water vapor in the MODIS atmospheric product MOD07_L2. BRDF parameters in the MODIS BRDF product MOD43B1C are also used in the V4 processing. The initial MOD11B1 product was released in July 2001. The V4 MOD11A1, MOD11A2, and MOD11B1 products generated from reprocessing of MODIS data since late February 2000 and forward processing of MODIS data since early 2003 were released in early 2003. The MODIS CMG LST products (MOD11C1-3) have been released recently (June 2003). Table 1. Summary of the MODIS LST data products.
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