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DESERTLINKS 2004 English-EN | Español-ES | Italiano-I | Ελληνικά-GR | Portuguese-PT |
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Σύστημα Δεικτών Ερημοποίησης για την Μεσογειακή Ευρώπη |
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g Indicators used at the national scale When assessing desertification threatened areas and the extent for their National Action Programmes, the Annex IV sub-region Focal Points each used 3 or 4 indexes which they mapped nationally. Most of them also mapped a further set of indicators at the regional scale. Most of the indexes or indicators in these lists are described in DIS4ME (as shown by links to the indicator database), sometimes under a slightly different name.
Source: Lúcio do Rosário (2004) Indicadores de Desertificação para Portgal Continental. Direcção-Geral dos Recursos Florestais. http://www.dgrf.min-agricultura.pt
g Desertification indicators obtained from remote sensing A broad range of potential remote sensing based desertification indicators has been discussed and reviewed, but especially those that refer to the issues and themes identified by stakeholders. Most remote sensing indicators relate to vegetation cover and its changes, but remote sensing can also address issues such as urban sprawl and organic matter content of the top-soil. Preference has been given to those indicators that can be obtained quasi-operationally by remote sensing alone, where the remote sensing component is central in indicator modelling or where we expect an increasing importance of remote sensing in the near future. A further criterion was knowledge of existing major European initiatives addressing an issue, such as in the case of urban sprawl or forest fire. The table below
lists indicators that have the strongest potential to be derived with
major contributions from remote sensing. Although the list is short,
it should be noted that there are a number of other issues and indicators
where remote sensing information may play a role (e.g. grazing, land
abandonment etc) in particular applied in combination with geomatics,
ecological and socio-economic modelling (as shown in the GeoRange and
LADAMER projects). The three final indicators have been added because
they have been identified by national Focal Points as being relevant
for important target areas in Annex IV countries. DESERTLINKS
indicators with the strongest potential for remote sensing applications
Remote sensing has
been used to investigate in what way and to what extent changing energy
and water fluxes at the land surface – atmosphere interface are
related to the assumed changes in climatic forcing of desertification
processes. Advanced techniques have been developed to accurately derive
standardised “primary” radiometric variables (e.g. spectral
reflectance, albedo, surface temperature, emissivity etc.) and to analyse
the temporal behaviour of these variables in terms of changing energy,
momentum and mass exchange between land and atmosphere [1] [2]. Instead
of the “climatic” approach, DESERTLINKS is aiming more at
the identification of changes of physical land surface conditions in
terms of vegetation cover and soil status. This approach also requires
the correct conversion of radiance registered by the remote sensing
sensor into primary physical variables (e.g. reflectance, land surface
temperature). Then the information on physical land surface status may
be derived both from remote sensing directly and through integration
of remotely sensed information with data from other sources. In particular
this may be achieved within a complex modelling framework such as the
Regional Degradation Index models for Mediterranean wide risk of water
erosion and salinisation. The requirement
for Regional Indicators is that they should be applied to the entire
Mediterranean basin at full coverage, giving a general overview at coarse
scale in order to identify areas where more detailed studies should
be performed. They should also have the potential to be regularly up-dated
for monitoring purposes. This implies that at this scale only the use
of a coarse resolution/high revisit rate (1 to 3 days) remote sensing
system such as NOAA-AVHRR (1 to 8 km resolution), SPOT VEGETATION (1
km), TERRA-MODIS (0.25 to 1 km) or MERIS (0.3 to 1 km) are realistic
options. Although, compared to the other systems, NOAA-AVHRR has a number
of shortcomings in radiometric and geometric accuracy, it is still a
central element in the indicator development and understanding of desertification
processes. This because it is the only system having 20 years history
of operation and thus it is crucial to building the backbone of the
necessary long term, multi-temporal analyses and base-lines. Newer systems,
nevertheless, assure continuity with the NOAA satellite data, and will
allow definite improvements to geo-referencing in relation to ground
information, and extended possibilities for deriving information on
vegetation and soil status. As regards validation
and calibration of regional scale indicators remote sensing offers a
strong potential for down-scaling from regional scale to target areas
by disaggregation of vegetation cover related information with the help
of higher resolution remote sensing data such as Landsat-TM and/or higher
resolution thematic data e.g. CORINE land cover. In particular, the
approach to derive fractional vegetation cover at different scales on
the basis of spectral mixture analysis (SMA) has shown that vegetation
cover has a fractal dimension which allows its comparison at different
scales. Although the dominant factors (controlling e.g. patterns of
vegetation) change at the different scales, the scientific rationale
for comparison could be given by applying concepts of ecosystem resilience
during given time periods, which are covered both by available coarse
resolution and high resolution satellite data over the DESERTLINKS target
areas.
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