FIGURE 6-1 The relationship between U.S. Geological Survey land-cover and land-use classes and the required spatial resolution of the imagery. SOURCE: Pearson Education, Inc., adapted from Jensen (2000).

interpretation techniques applied to analog (hard-copy) imagery or digital image processing techniques applied to digital remote-sensor data (including digitized aerial photography) (Jensen, 1996).

The following discussion begins with a brief overview of the importance of high spatial resolution aerial photography and satellite imagery to obtain detailed Level III and IV land-cover and land-use information for urban applications and progresses to lower spatial resolution imagery for regional and global applications (mainly associated with Levels I and II). Several sources of remotely sensed data may be available for a given spatial resolution. This discussion deals primarily with publicly available and commercial sources from the United States.

Urban and Suburban Land Cover and Land Use

Many Agenda 21 issues concentrate on urban and suburban areas (Table 2-5). The detailed land-use and land-cover information needed in these settings is derived from high spatial resolution aerial photography or satellite imagery (Table 6-1, Figure 6-2). Since 1994, such companies as Space Imaging and DigitalGlobe have marketed high spatial resolution satellite data (approximately 1 × 1 m to 4 × 4 m) (Annex Box 6-1). Examples of Space Imaging’s IKONOS imagery are shown in Figure 6-3.

Ways need to be found to make high spatial resolution imagery accessible to users in Africa. Currently, these data are expensive (Table 6-2), and more affordable, lower spatial resolution imagery is an inadequate substitute in urban environments.

Regional and Global Land Cover

The land cover of much of Africa can be inventoried using medium to coarse spatial resolution satellite imagery (e.g., 20 to 1000 m). Normally this imagery must be multispectral. This section discusses five sources of these data, all of which can be obtained inexpensively. Additional resources can be found at the World Data Center for Remotely Sensed Land Data.1

Land-Cover Data Source A: Advanced Very High Resolution Radiometer (AVHRR) Imagery

NOAA’s AVHRR is a widely used source of satellite data for natural resource management and early warning systems in Africa. This class of sensor flies onboard NOAA’s operational satellites (Annex Box 6-2), and will likely continue operating until 2018 (Annex Box 6-3). AVHRR is a sustained source of low-cost data with a spatial resolution of ~1 × 1 km.

The Global Land Cover Dataset

AVHRR images from 1992 and 1993 are the source for the Global Land Cover dataset. The dataset was compiled for broad use in environmental research and modeling (Loveland et al., 2000). It was developed by IGBP Data and Information Systems Focus 1 activity (Townshend and Skole, 1995)2 and implemented by the USGS EROS Data Center, the European Commission’s Joint Research Centre,

1  

<http://edc.usgs.gov/doc/edchome/world/wdcguide.html>.

2  

Funding for the project is provided by the NASA, NOAA, the U.N. Environment Programme, U.S. Environmental Protection Agency, U.S. Forest Service, USGS, and European Space Agency.



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