An overview of MODIS Land data processing and product status
Introduction
To continue a strong commitment to the US space program, the National Aeronautics and Space Administration (NASA) has undertaken a program of long-term observation, research, and analysis of the Earth's land, oceans, atmosphere and their interactions, including measurements from the Earth Observing System (EOS) Kaufman et al., 1998, NASA, 1999. The EOS is funded by the NASA Earth Science Enterprise (ESE) Program and has three main components, (i) a coordinated series of Earth-observing satellites, (ii) an advanced data system designed to support the production, archival, and dissemination of satellite derived data products, (iii) teams of scientists who are developing the science algorithms to make the data products. The Moderate Resolution Imaging Spectroradiometer (MODIS) is a key instrument onboard the EOS Terra satellite, successfully launched in December 1999, and will be complemented by another MODIS on the EOS Aqua satellite to be launched in 2002.
The MODIS instrument data are converted on a systematic basis into derived atmospheric, terrestrial and oceanic products. This paper overviews the status of the MODIS instrument on the Terra platform, the production of land products derived from MODIS data, and availability of these products generated from algorithms developed by the land science team. More detailed descriptions of the individual MODIS land (hereafter termed “MODland”) products are found in the papers in this special MODIS Land issue of Remote Sensing of Environment.
Since the Terra launch in December 1999, the MODIS Science Team has made significant progress in characterizing the performance of the first MODIS instrument, providing the MODIS instrument data (Level 1B), generating and assessing the quality of higher order geophysical products (Levels 2, 3 and 4), initiating product validation and preparing for the launch of the second MODIS instrument on the EOS Aqua platform. The Team scientists responsible for the delivery of code and the creation of MODland products, has generated a new suite of moderate-resolution land products in support of global change research and natural resource applications (Table 1). These products support directly NASA's Earth Science Enterprise's systematic measurement program (NASA, 1999). The overall goal of the Earth Science Enterprise is to determine how the Earth is changing and what are the consequences for life on Earth. The land products from MODIS lay the foundations for long-term land surface monitoring. This has been accomplished primarily through the generation of products that are prototypes for those from the next generation of operational sensing systems, supported by the US National Polar Orbiting Environmental Satellite System (NPOESS). Research on the Advanced Very High Resolution Radiometer (AVHRR) has provided much of the methodological underpinning and experience-base for MODland product development. However, reliance on the AVHRR and its associated spectral and geometric constraints has limited the ability of the land research community to develop the range of products needed for global change research (Cihlar, 1997). The MODland products will enable the global change research community to address a much broader range of questions associated with biogeochemical cycling, energy balance, land cover change and ecosystems (Table 3, WWW1). The MODland products will also be used for regional and global applications.
Section snippets
The MODIS instrument
One of NASA's roles is to provide a test bed for new technologies. With 36 spectral bands and 12-bit radiometric resolution, MODIS has the highest number of spectral bands of any global coverage moderate resolution imager. The design of MODIS was an inevitable compromise to satisfy the requirements of the three different disciplines: atmosphere, ocean and land, with spectral bands and spatial resolution selected to meet different observational needs and provide near-daily global coverage
The MODIS Land products
The land products for MODIS were selected in a peer review process in 1992, based on scientific priorities established in the late 1980s. This was at a time when Mission to Planet Earth was a major science theme of NASA Committee on Earth Sciences, 1995, Running et al., 1994. The initial product suite and the algorithms have been externally reviewed twice and refined since initial selection, resulting in the loss of a polarization product and the addition of ‘vegetation continuous fields’ and
The data production system
The EOS Data Information System (EOSDIS) is designed to provide the computing and network facilities to support NASA's EOS research activities, including processing, distributing, and archiving EOS data; exchanging research results among scientists; and commanding and controlling the spacecraft instrumentation. The EOSDIS Core System (ECS) provides the computing architecture to accomplish these goals. Data Active Archive Centers (DAACs) are responsible for running the ECS. At the beginning of
Land product quality assessment, validation and availability
The EOS product distribution policy is to make products available to the user community in a timely manner, with information on product errors, artifacts and accuracy. Members of the Science Team are responsible for the quality assessment (QA) and validation activities required to define these information. At the time of writing, all but two of the MODland products are available to the user community. The remaining two products (NPP and Vegetation Cover Change), which are about to be released,
Conclusion
It takes time for new land products derived from a new sensor system to be adopted by users. The user community was relatively slow to adopt products derived from the AVHRR. In retrospect, products from the AVHRR led arguably the most significant advances in land remote sensing during the late 1980s and 1990s and they gave users the ability to develop and use time-series moderate resolution data providing the basis for terrestrial global scale monitoring. However, widespread use of the products
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