Global Monthly Vegetation Cover CD-ROM (Version 1.1) ------------------------------ 1. Introduction Welcome to the National Climatic Data Center's (NCDC) Global Monthly Vegetation Cover (Version 1.1) CD-ROM. This CD-ROM contains data that were generated from the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR) instrument. These data were further processed into Normalized Difference Vegetation Index (NDVI) data. This CD-ROM was jointly produced by NOAA's Office of Research and Applications/Climate Research and Applications Division/ Land Surface Team and National Climatic Data Center /Climate Services Division/Satellite Services Branch. Version 1.1 corrects problems with the original CD-ROM Version 1.0 dated January 1998. This CD-ROM contains a 12-year time series of global monthly mean NDVI data reprocessed from the AVHRR measurements. This data set is based on the weekly composite maps produced within the Global Vegetation Index (GVI) project in the Office of Research and Applications, National Environmental Satellite Data and Information Service (NESDIS), National Oceanic and Atmospheric Administration (NOAA). The GVI project was sponsored by the NOAA Climate and Global Change Program for the purpose of developing improved operational GVI products that are useful for global climate studies. The data on this CD-ROM are the GVI C3.2/M15 NDVI product (for the nomenclature, see Gutman et al. 1995, which is included on this CD-ROM), which are also known as the Third Generation C-Level GVI data (see the NOAA Global Vegetation Index User's Guide). The products are given at 0.15 degree resolution in a rectangular latitude/ longitude (equal angle) projection (also known as Plate Carree projection) and comprise NDVI monthly maps for the period of April 1985 - December 1997. Also included on this CD-ROM are monthly Quality Description (QD) files containing compressed information on the monthly mean satellite viewing and solar zenith angles, which may be useful in identifying geometry biases, and the number of weeks used to calculate monthly statistics for each individual year after cloud screening. In addition, a stationary file (one for all the months) is included consisting of auxiliary masks (AM) that contain land/sea tag, political boundaries and two masks based on maximum (Vmax) and minimum (Vmin) annual NDVI values characterizing low annual variability in NDVI (Vmax-Vmin<0.2) for evergreen (Vmax>0.45) and deserts (Vmax<0.2). To facilitate geophysical analysis, gif files of the data and an offline browser (Navroad) are included on this CD-ROM. The data processing is briefly described below. Its full description is given in Gutman et al. 1995. Programs to read the data on several platforms and their documentation are also included on this CD-ROM. 2. Brief Data Processing Description The processing of weekly data (B3.0/W15 --> B3.2/W15) was based on the GVI weekly composite raw (counts) data -- the Second Generation of GVI -- and is described in the NOAA Global Vegetation Index User's Guide (Kidwell 1997) and in Gutman et al. 1995. It included calibrated visible and near-infrared data using updated coefficients (Rao and Chen, 1995, 1996), and development of Quality/Cloud masks (Gutman et al. 1994) for each composite, appended but not applied. The monthly processing (B3.2/W15 --> C3.2/M15) flow included the following steps: 1) Quality/Cloud flags were applied on a weekly basis, resulting in data gaps, 2) NDVI was averaged over one month (five weekly composites) for each map cell to partially fill in the data gaps and reduce some of the angular variability (the weeks that spill over into the next month were used for both the current and the previous months); 3) bi-linear spatial interpolation was applied to the missing data areas with persistent cloudiness in monthly averaged images; 4) 3x3 map cell running average smoothing was done to partially account for the imperfection of cloud screening, to filter out atmospheric and angular variabilities, and to compensate for different number of observations used in monthly averaging and for random spatial sampling from the original Global Area Coverage (GAC) data into the GVI map cells. Note that the NDVI data were produced from the top-of-the-atmosphere radiances, i.e. no angular/atmospheric corrections were applied except for cloud screening. The green vegetation fraction, fg, can be derived from NDVI using a simple linear relationship with an assumption of dense vegetation (high leaf area index) (Gutman and Ignatov 1998). fg = (NDVI - NDVImin) / (NDVImax - NDVImin) where NDVImin=0.04 and NDVImax=0.52 are prescribed as global constants (Gutman and Ignatov 1998) as a first approximation. The values of fg should be restricted to be between 0 and 1. The conversion to fg is merely a rescaling of NDVI for a more convenient analysis, but is not absolutely necessary. 3. Disc Contents This disc is arranged as a series of HTML files that are linked to each other through the Welcome page (intro.htm). The Welcome page has the following links: Revision Information - contains a list of files that were replaced from the original (Version 1.0) CD-ROM. Technical Information - contains files describing the organization and contents of the CD-ROM, software for an off-line browser and information on ordering this CD-ROM from NCDC Preface - contains detailed information on the data itself, how it was processed and acknowledgments to the individuals involved Digital Data Information - contains the formats for: the 8-bit digital data, the Quality Description files and Auxiliary Mask files plus software (FORTRAN and C) to read the 8-bit digital data using different platforms 3rd Generation C-level NDVI Imagery - contains an image for each month of the time series with the name of the corresponding digital dataset file (which are included on the CD-ROM). Reprint of the 'The Enhanced NOAA Global Land Dataset from the Advanced Very High Resolution Radiometer' Paper - 1995 reprint of Bulletin of American Meteorological Society paper which explains exactly how the data were processed and the nomenclature used in the CD-ROM References - sources used in the creation of this CD-ROM. Acknowledgment - thanks to the individuals involved in producing the CD-ROM Disclaimer - NOAA cannot assume any liability for any damages incurred 4. How to Use This Disc This ISO-9660 format CD-ROM disc was designed for use with any computer that supports a World Wide Web browser capable of supporting embedded graphics and the HTML v3.2 draft specification. Any browser that meets the HTML v3.2 draft specification will produce satisfactory results, although the appearance of the document (e.g. font size and color) may vary depending upon the browser and site customizations. This disc was tested with the following browsers and operating systems: * Microsoft Internet Explorer v3.0x - Microsoft Windows 95; * NCSA Mosaic 2.7b5 - Unix (Linux, see NOTE 1 below); * NCSA Mosaic 3.0 - Microsoft Windows 95 (see NOTE 2 below); * Netscape Navigator v2.0 - Microsoft Windows 3.1, Microsoft Windows 95; * Netscape Navigator v3.0 - Microsoft Windows 95, Unix (AIX). NOTE 1: NCSA Mosaic 2.7b5 for Unix does not display images and links embedded within tables if Table Support is enabled. Disable Table Support to access these images and links. NOTE 2: NCSA Mosaic 3.0 for Windows 95 may display a "Failed to find internal anchor" error messages on some links. Click OK and press "r" to reload the page cleanly. This document does not describe how to install and use a Web browser; see the documentation included with your browser for this information. If you do not have a Web browser or Internet access, NCDC has included on this disc licensed copies of FAICO Information Solutions' NavRoad offline HTML browser for Microsoft Windows 3.1 and Windows 95 systems. For more information on this software, please read the navroad.txt file in the root directory (/) of this disc. To view the documents and images on this disc, run your browser and open the intro.htm file in the root directory (/) of the Global Monthly Vegetation Cover CD-ROM. This will display the Welcome Page for the disc, from which you can explore links to the image collections and the digital data. When an Internet site is explicitly mentioned, the site address may be linked for your convenience. However, you must be using an Internet-ready browser and have an Internet network connection to follow the link to the site. 5. Technical Support Questions about the NavRoad offline browsers should be directed to FAICO Information Solutions. Please see the navroad.txt file in the root directory (/) of the CD-ROM for contact information. Questions about the installation and use of specific document browsers should be directed to the technical support resources provided by the publisher of that browser. NCDC is not equipped to address browser-specific questions. Technical support for the information provided on this CD-ROM is available from NCDC's Satellite Services Group. Comments, corrections, questions and product requests should be directed to: SATELLITE SERVICES GROUP NATIONAL CLIMATIC DATA CENTER 151 PATTON AVE RM 468 ASHEVILLE NC 28801-5001 USA Telephone: +1-828-271-4850 Hours: Monday through Friday, 7:30 AM to 4 PM US Eastern Time Facsimile: +1-828-271-4876 E-mail: satorder@ncdc.noaa.gov Web Site: http://www.ncdc.noaa.gov/psguide/satellite/sathome.html If there are any future problems with this CD-ROM they will be noted in the "Amendments" section of the following website: http://www2.ncdc.noaa.gov/docs/ndvisamp/intro.htm Further information on Vegetation Index data can be obtained by contacting: DR. J. DAN TARPLEY NOAA/NESDIS/ORA CLIMATE RESEARCH AND APPLICATIONS DIVISION LAND SURFACE TEAM NOAA SCIENCE CENTER, RM. 712 CAMP SPRINGS, MD 20233 USA 6. Acknowledgments The GVI project has been supported by the NOAA Climate and Global Change Program (CGCP). Without its continuous funding, the generation of the 12-year GVI data over land would not have been possible. The following individuals developed this new data set: Garik Gutman, Dan Tarpley, Aleksandr Ignatov (all from Office of Research and Applications, NOAA/ NESDIS, Washington, D.C.) and Steve Olson of Research and Data Systems Corporation (RDC). Critique and reviewing by the NOAA CGCP manager, Dr. A. Gruber, motivated this work. D. Sullivan (RDC) and J. Powers (NESDIS) are also 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. Special thanks go to those who assisted in producing this CD-ROM: Jeannette Rivera and Dee Lallemont for organizing and creating the html files, Curt Benner and Geof Goodrum for their help with the README files, Garry Ayres for obtaining the NDVI files from NCDC's archive, Ralph E. Meiggs for creating the numerous .gif images from the archive files, Jeff Robel for placing the NOAA logo on all the images and Kathy Kidwell for general editing (all from the Satellite Services Branch of NCDC's Climate Services Division in Suitland, MD). Special thanks are also extended to Ann Hallyburton (NCDC, Asheville, NC), who provided the art work for the disc cover on the jewel case. Dr. Ivan Csiszar, Dave Forsyth (Office of Research and Applications, NOAA/NESDIS), and Dr. Rikie Suzuki (Frontier Research System for Global Change, National Research Institute for Earth Science and Disaster Prevention, Ibaraki, Japan) deserve special mention and thanks for reviewing Version 1.1 to ensure it's accuracy before distribution. The requested form of acknowledgment for use of the data on this CD-ROM should be as follows: Time Series of Global Monthly Vegetation Cover from NOAA/AVHRR: April 1985-December 1997, February 2001, Version 1.1, NOAA National Climatic Data Center. Published on CD-ROM by NOAA/NESDIS/NCDC. 7. References Gutman, G., A. Ignatov and S. Olson, 1994: Towards better quality of AVHRR composite images over land: Reduction of cloud contamination, Remote Sens. Env., 50: 134-148. Gutman, G. and A. Ignatov, 1998: Derivation of green vegetation fraction from NOAA/AVHRR for use in weather prediction models, Int. J. Rem. Sens., 19: 1533-1543. Gutman, G., D. Tarpley, A. Ignatov and S. Olson, 1995: The enhanced NOAA Global Land datasets from the Advanced Very High Resolution Radiometer, Bull. Amer. Meteorol. Soc., 76: 1141-1156. Kidwell, K., 1997: NOAA Global Vegetation Index User's Guide, U.S. Dept. of Commerce, NOAA/ National Environmental Satellite Data and Information Service, National Climatic Data Center, Satellite Services Branch, pp. 204. Rao, C.R.N., and J. Chen, 1995: Inter-satellite calibration linkages for the visible and near-infrared channels of the Advanced Very High Resolution Radiometer on the NOAA-7, -9, and -11 spacecraft, Int. J. Rem. Sens., 16, 1931-1942. Rao, C.R.N., and J. Chen, 1996: Post-launch calibration of the visible and near-infrared channels of the Advanced Very High Resolution Radiometer on the NOAA-14 spacecraft, Int. J. Rem. Sens., 17, 2743-2747.