Land Properties


Surface Temperatures

This image represents mean global surface temperatures for June 1988 and was derived using data from the High Resolution Infrared Radiation Sounder (HIRS-2) and Microwave Sounding Unit (MSU) carried on a NOAA Polar-orbiting Operational Environmental Satellite. Warmest temperatures are indicated by reds; cooler temperatures are indicated by yellows, greens, blues, and purples, in descending order.

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Topography

Knowledge of the topography of the Earth's surface is important for many EOS studies. On a global scale, topography affects the circulation of the atmosphere and ocean water. The topography of continents affects the gravity field, the interpretation of which, in turn, provides information on the geology and structure of the land. Locally, the topography must be known in order to predict areas of flooding, the distribution of vegetation types, and the degree of soil erosion to be expected.

The hue and saturation of colors in this image are controlled by the depth or elevation of the land. The colors indicate the depth, from darkest blue the deepest to bright red the highest points.

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Vegetation

Global vegetation plays a key role in sustaining life on Earth. We have just begun to understand how the thin film of living matter on Earth is sustained by global-scale biogeochemical cycles. Closely related to the biogeochemical cycles are changes in the populations of life forms within the ecosystems of the world, both in numbers of species and in the abundance of individuals within the species.

Although changes in populations of life forms are not new, it is apparent that they are now occurring at an accelerated rate, and that human beings, comparatively recent agents of global modification, are likely the cause of most of this accelerated change. In order to maintain the conditions desirable for human habitation it is important that we understand the role of natural biological diversity in maintaining the global balance of the environment and the extent to which the world's ecosystems are being affected by human activities.

The images above are as follows:

GLOBAL BIOPHYSICS

NOAA Advanced Very High Resolution Radiometer (AVHRR) data processed into normalized difference vegetation index (NDVI) for August 1987. Dark-blue areas represent dense vegetation, pale blues and greens represent light vegetation, and pink and dark-red areas represent sparse vegetation.

LEAF AREA INDEX

The NDVI data have been analyzed to calculate global monthly fields of green leaf area index (square meters of green leaves per square meter of surface). Green represents dense vegetation, while brown indicates desert.

VEGETATION TYPE

Seasonal variations in the NDVI as observed by NOAA AVHRR can be analyzed to establish a global vegetation classification. The major biomes are shown in this analysis: tropical forests, deserts, agriculture, northern forests, etc. Purple and green areas represent dense vegetation, tan areas represent sparse vegetation.

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Vegetation Dynamics

As plants and trees grow, photosynthesisinvolving the interaction of sunlight, chlorophyll in green leaves, carbon dioxide, and waterresults in a net removal of carbon dioxide from the atmosphere and the release of oxygen as a by-product. Also, moisture is released to the atmosphere through evapotranspiration.

When forests die and decay, or are burned, the biomass is oxidized and carbon dioxide is returned to the atmosphere.

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Global Vegetation Index

A key scientific issue is the role of terrestrial ecosystems in absorbing the excess atmospheric carbon dioxide generated by mankind since the beginning of the industrial revolution. To investigate this, a global perspective is needed.

An example of the kind of data used for such investigations is found in this image, which depicts the state of vegetation during August 1987. Dark-blue areas represent dense vegetation, paler blues represent lighter vegetation, and pink and dark-red areas represent sparse vegetation.

In the future, the Moderate-Resolution Imaging Spectroradiometer (MODIS) on the EOS satellites and the Enhanced Thematic Mapper Plus (ETM+) on Landsat-7 will provide such information routinely as part of the Earth Science Enterprise Program.

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