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Global Monthly Vegetation CoverReprint of Original Document |
Introduction Page,
6. Conclusions
An overview of research and development with the NOAA global vegetation index dataset under a core project of the NOAA Climate and Global Change Program has been given and the enhanced GVI data products described. All the products (B3.2/W15, C3.2/M15, and D3.2/M15) are available from NOAA archives. The D3.2/M15 will also be available on CD/ROM. The C3.2/M15 and D3.2/M15 products reside on a UNIX system at NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) and will be made available for browsing and animation. The latter can be used for educational purposes to illustrate the global annual dynamics of vegetation cover, albedo, temperature, and water vapor.
The newly derived C and D products can be easily accessed by climatologists for the analysis of inter- and intra-annual land climate variability, such as response of the surface state to ENSO episodes. Deeper involvement of climatologists in the data products analysis and their close interaction with the "data producers" is imperative at this stage. Given the improvement of the data quality, the present study suggests that there is more potential in this dataset than previously thought (e.g. Thomas and Henderson-Sellers 1987), although it should be borne in mind that the remaining uncertainties limit this potential. The annual global distribution of the GVI variables is currently more reliable than the derived interannual variability, which is useful only when the surface change is relatively strong compared to the noise level. Further reduction of noise and removal of trends will increase the monitoring potential of AVHRR land data.
The operational production of monthly anomalies continues. The previous month's anomalies are available during the first week of the current month. Weekly monitoring for the areas with frequent cloud-free skies can be developed if more progress is achieved in angular/atmospheric corrections.
Despite the remaining uncertainties in the monthly GVI data products, their information content is higher than that of the GIMMS-derived 1o x 1o NDVI monthly dataset (Los et al. 1994) because of finer spatial resolution, the availability of individual channel reflectances and temperatures, and more accurate cloud screening. The GVI dataset is unique in that it is global, multiseasonal, multispectral, and multiannual. These GVI features are useful not only for environmental studies and numerical modeling, but also for further development of the remote sensing methodology and processing of the 8-km Pathfinder and 1-km IGBP AVHRR datasets. Both Pathfinder and the 1-km projects can utilize the GVI experience for generating C- and D-level products for the environmental research community. Development of the GVI data products contributes to the activities within IGBP, GEWEX, and, particularly, ISLSCP.
Acknowledgments. The GVI project has been supported by the NOAA Climate and Global Change Program. Without its continuous funding, the construction of the UNIX-based system for generating global AVHRR land data products would not have been possible. Critique and reviewing by the NOAA CGCP manager, Dr. A. Gruber, motivated this paper. D. Sullivan [Research Data Systems Corporation (RDC)] and J. Powers (NESDIS' Interactive Processing Branch) are acknowledged for the development of the processing and visualization system. Contributions in the project by M. Halpert and Dr. C. Ropelewski (NOAA Climate Analysis Center), and P. Schultz, R. Hucek and L. Rukhovetz (RDC) are acknowledged. Reviews by Drs. G. Ohring (NOAA/NESDIS), J. Price (USDA), D. Hastings (NOAA/NGDC) and three anonymous reviewers are appreciated. Comments by Dr. L. Stowe (NOAA/NESDIS) on the processing structure and nomenclature are appreciated. This work was prepared for publication when one of the authors (A.I.) held National Research Council Associateship at the Satellite Research Laboratory, NOAA/NESDIS, on leave from the Marine Hydrophysics Institute, Sevastopol, Ukraine.
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