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Introduction
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Soil Temperature
Alaska
Russia
Snow Cover
Snow Off Day
Greenness
SINDVI
Nascence
Peak
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Greenness: Seasonally Integrated NDVI
Seasonally integrated NDVI (SINDVI) is NDVI integrated over the growing
season. We count the growing season as beginning when NDVI crosses a
threshold value of 0.3 (the same value used to indicate nascence). North
of 50 degrees latitude, this usually occurs between late May and the
beginning of July. The season ends when NDVI drops below 0.3 as senescence
occurs.
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Average SINDVI The
mean seasonally integrated NDVI over the period 1982 - 2001. From
the Pathfinder data set. |
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Current SINDVI SINDVI
for the last growing season. From the MODIS data set. See Continuing
the time series with MODIS data for discussion of differences
with Pathfinder data. |
SINDVI Anomaly, First Five Years Pathfinder
Data Minus Mean
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SINDVI Anomaly, Last Five Years Pathfinder
Data Minus Mean
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Notes: The anomaly images above show the widespread
greening that has taken place in the late 1990s relative to the mid 1980s,
marked by the predominance of negative (brown) values on the left and
positive (blue) values on the right. (The grey areas in the images are
where the threshold of 0.3 was not exceeded. Shield, bare rock, ice sheets,
and areas largely covered by water have low or zero NDVI.) See Continuing
the time series with MODIS data for discussion of why more recent
MODIS data are not used.
SINDVI Time Series, Average Regional
Values |
SINDVI Anomaly Time Series, Average
Regional Values |
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Notes: Time series of SINDVI values (left) and anomalies
(relative to the 1982-2001 mean, right) for regional subsets (red squares
in the images) show a general upward trend in greenness that is fairly
well correlated from place to place. The downward spike at all locations
in 1992 reflects the residual effect of the 1991 Mt. Pinatubo volcanic
eruption. (Smaller SINDVI values in 1992-1994 remained in many NDVI data
sets even after attempts to correct for Pinatubo's effects on AVHRR-derived
NDVI, and primary production may have been reduced as a result of increases
in stratospheric aerosols, according to Stow et al., 2003). The dashed
lines are data from MODIS. See Indicator
Processing and Discussion for more information.
SINDVI, North Slope,
AK Subregions |
SINDVI Anomalies,
North Slope, AK Subregions |
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Notes: The North Slope, AK section was divided into
subsections based on literature suggesting a different greening response
for coastal versus inland tundra (see Discussion).
Coastal tundra SINDVI differs from inland higher elevation tundra SINDVI
by a factor of 1 to 2. The large number of lakes near the coast is one
reason for the difference, but other reasons such as differences in soil
and vegetation type are at play as well. The anomaly series show that
in spite of different greenness values, the two physiographical provinces
are responding to changes quite similarly. A more detailed study might
yield different results with higher resolution data (For example, Stow
et al, 2003, find a difference in the rate of change of greenness between
the two areas when a 3 km AVHRR data set is used.) The overall increase
in SINDVI on the North Slope has been attributed to warmer air temperatures,
earlier snow melt, and greater shrubbiness (Walker et al., 2003). |
