Almost 400 images
from the NOAA AVHRR sensor recorded between 21st and 30th June 1992 were calibrated
and processed to give a global Normalised Difference Vegetation Index (NDVI)
which shows the greenness of the world's vegetation (green represents vigorous,
healthy vegetation, yellow shows dry biomass while brown indicates no, or
sparse vegetation).
These data were compiled by the U.S. Geological Survey in co-operation with
other agencies and ground receiving stations around the world and provides an
un-biased
means to analyse
and monitor the effects of droughts and long term changes from possible regional
or global
climate change.
Ozone Distribution (left)
The Global Ozone Monitoring
Experiment (GOME) sensor was launched in April 1995 on the European ERS-2 satellite.
This instrument can measure a range of atmospheric trace
constituents, such as sulphur dioxide and nitrous oxide, but has an emphasis
on the measurement of global ozone distributions. Many applications need information
on the
ozone distribution in near real time. For example, TV-media, environmental and
public health authorities need this up-to-date information to early warn people
against health
risks since low total column ozone implies increased ground-level UV-B radiation
(UV-B is biologically harmful and can create cancers, cataracts and impacts
the human immune system).
Gravitational Fields (right)
The strength of the
earth's gravitational field at its surface varies according to the
ocean depth and the density of local rocks. Dense rocks and shallow ocean, such
as along the Mid-Atlantic Ridge (shown in red in the image), creates a higher
local gravitational
force which causes a greater 'pull' on the surrounding ocean water and thus
results in a higher local sea level. Satellites orbiting in very precisely
determined
orbits are able
to measure the sea level to an accuracy of a few centimetres by using Radar
Altimeters which transmit microwave pulses and time their return. This measurement
of the
results
of gravitational variations gives us a better picture and understanding of
the geological structure of the sea floor. From the time variation of the returned
signal Altimeters
can also build up a model of ocean wave heights, which relate to surface wind
speed. Radar Altimeters therefore also provide valuable data useful in meteorological
forecasting.
Weather Monitoring (left and right)
Geostationary
and polar orbiting satellites continuously monitor the Earth's cloud and
atmospheric moisture movements providing us with the means to predict our weather
with high level of reliability. The progress of severe tropical storms such
as Hurricane
Andrew (right) can be tracked from their development in the middle of the Atlantic
Ocean and as they progress towards the Caribbean and Southeast United States.
This
advance warning enables property to be protected and lives saved.
