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University of Nebraska–Lincoln


Channel
NDVI
1
2
3
4
5
Wavelength (m)

0.58-0.68
0.73-1.10
3.55-3.93
10.3-11.3
11.5-12.5
Description
See Below
Reflectance
Reflectance

Brightness Temp.
Brightness Temp.
Units
Unitless
%
%

Kelvin
Kelvin
Data Range
-1 to +1
0 to 100
0 to 100

160 to 340
160 to 340
Orbit
Polar
Period
102 minutes
Orbits Per Day
14.1
Resolution
8 km x 8 km



The orbital period of about 102 minutes produces 14.1 orbits per day. Because the daily number of orbits is not an integer, the suborbital tracks do not repeat daily, although the local solar time of the satellite's passage is essentially unchanged for any latitude. The 110.8 degrees cross-track scan equates to a swath of about 2700 km. This swath width is greater than the 25.3 degrees separation between successive orbital tracks and provides overlapping coverage .

THEORETICAL BASIS OF DATA

Spectral Wavelengths

On the NOAA-7, NOAA-9, and NOAA-11 satellites, the AVHRR sensor measures emitted and reflected radiation in five channels (bands) of the electromagnetic spectrum: a visible (0.58 to 0.68 micrometer) band that is used for daytime cloud and surface mapping; a near-infrared (0.725 to 1.1 micrometer) band used for surface water delineation and vegetation cover mapping; a mid-infrared (3.55 to 3.93 micrometer) band used for sea surface temperature and nighttime cloud mapping; a thermal infrared (10.5 to 11.5 micrometer) band used for surface temperature and day and night cloud mapping; and another thermal infrared (11.5 to 12.5 micrometer) band used for surface temperature mapping.

Vegetation Index

The first AVHRR channel is in a part of the spectrum where chlorophyll causes considerable absorption of incoming radiation, and the second channel is in a spectral region where spongy mesophyll leaf structure leads to considerable reflectance. This contrast between responses of the two bands can be shown by a ratio transform; i.e., dividing one band by the other. Several ratio transforms have been proposed for studying different land surfaces . The Normalized Difference Vegetation Index (NDVI) is one such ratio, which has been shown to be highly correlated with vegetation parameters such as green-leaf biomass and green-leaf area and, hence, is of considerable value for vegetation discrimination.

This data set product (NDVI) is particularly useful for studies of temporal and interannual behavior of surface vegetation and for developing surface background characteristics for use in climate modeling. Some uses of NDVI include:

  • Global land cover classification.
  • Regional agricultural crop monitoring.
  • Desertification studies and drought monitoring.
  • Terrestrial environmental monitoring.
  • Global water and energy balance studies.