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Influence of solar zenith angles on observed trends in the NOAA/NASA 8-km Pathfinder normalized difference vegetation index over the African Sahel

Lindström, Johan LU orcid ; Eklundh, Lars LU ; Holst, Jan LU and Holst, Ulla LU (2006) In International Journal of Remote Sensing 27(9-10). p.1973-1991
Abstract
The strong systematic change in solar zenith angles (SZA) due to annual orbital drift of the NOAA satellites has raised the suspicion of the influence of residual illumination on the calibrated normalized difference vegetation index (NDVI) derived from the Pathfinder AVHRR Land (PAL) database. The aim of this work is to analyse if trends in AVHRR NDVI from 1982 to 2000 over the Sahel region in Africa depend on variations in SZA. The analysis uses both ordinary least squares regression and cointegration to analyse possible linear dependencies between NDVI and SZA on a per satellite basis. Tests for integration and cointegration fail to find any significant evidence for either. This, together with the ability of simple deterministic models... (More)
The strong systematic change in solar zenith angles (SZA) due to annual orbital drift of the NOAA satellites has raised the suspicion of the influence of residual illumination on the calibrated normalized difference vegetation index (NDVI) derived from the Pathfinder AVHRR Land (PAL) database. The aim of this work is to analyse if trends in AVHRR NDVI from 1982 to 2000 over the Sahel region in Africa depend on variations in SZA. The analysis uses both ordinary least squares regression and cointegration to analyse possible linear dependencies between NDVI and SZA on a per satellite basis. Tests for integration and cointegration fail to find any significant evidence for either. This, together with the ability of simple deterministic models to explain primarily SZA constitutes evidence against integration and cointegration, indicating that linear relationships can be examined using ordinary linear regression. Regression gives no consistent relationship between NDVI and SZA and the explanatory power (R 2) of the regression is low (on average 0.08). However there is some evidence for downward bias in NDVI due to nonlinear interactions between NDVI and SZA when SZA is large (>= 80 degrees) leading to the conclusion that PAL data from the year 2000 should not be used for analyses in these environments. (Less)
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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
International Journal of Remote Sensing
volume
27
issue
9-10
pages
1973 - 1991
publisher
Taylor & Francis
external identifiers
  • wos:000238652700017
  • scopus:33747160157
ISSN
1366-5901
DOI
10.1080/01431160500380539
language
English
LU publication?
yes
id
6773cf15-5547-4967-abb5-5fcc458e6c28 (old id 404918)
date added to LUP
2016-04-01 11:40:20
date last changed
2021-02-17 04:05:34
@article{6773cf15-5547-4967-abb5-5fcc458e6c28,
  abstract     = {The strong systematic change in solar zenith angles (SZA) due to annual orbital drift of the NOAA satellites has raised the suspicion of the influence of residual illumination on the calibrated normalized difference vegetation index (NDVI) derived from the Pathfinder AVHRR Land (PAL) database. The aim of this work is to analyse if trends in AVHRR NDVI from 1982 to 2000 over the Sahel region in Africa depend on variations in SZA. The analysis uses both ordinary least squares regression and cointegration to analyse possible linear dependencies between NDVI and SZA on a per satellite basis. Tests for integration and cointegration fail to find any significant evidence for either. This, together with the ability of simple deterministic models to explain primarily SZA constitutes evidence against integration and cointegration, indicating that linear relationships can be examined using ordinary linear regression. Regression gives no consistent relationship between NDVI and SZA and the explanatory power (R 2) of the regression is low (on average 0.08). However there is some evidence for downward bias in NDVI due to nonlinear interactions between NDVI and SZA when SZA is large (>= 80 degrees) leading to the conclusion that PAL data from the year 2000 should not be used for analyses in these environments.},
  author       = {Lindström, Johan and Eklundh, Lars and Holst, Jan and Holst, Ulla},
  issn         = {1366-5901},
  language     = {eng},
  number       = {9-10},
  pages        = {1973--1991},
  publisher    = {Taylor & Francis},
  series       = {International Journal of Remote Sensing},
  title        = {Influence of solar zenith angles on observed trends in the NOAA/NASA 8-km Pathfinder normalized difference vegetation index over the African Sahel},
  url          = {http://dx.doi.org/10.1080/01431160500380539},
  doi          = {10.1080/01431160500380539},
  volume       = {27},
  year         = {2006},
}