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Relation between Seasonally Detrended Shortwave Infrared Reflectance Data and Land Surface Moisture in Semi‑Arid Sahel
Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
The International Research Institute, Columbia University, 61 Route 9W, Palisades, NY 10964, USA
Centre d'Etudes Spatiales de la BIOsphere (CESBIO), UMR 5126 UPS-CNRS-CNES-IRD, 18 Avenue Edouard Belin, bpi 2801, F-31401 Toulouse Cedex 9, France
Department of Physical Geography and Ecosystems Science, Lund University, Sölvegatan 12, SE-22362 Lund, Sweden
* Author to whom correspondence should be addressed.
Received: 18 April 2013; in revised form: 23 May 2013 / Accepted: 23 May 2013 / Published: 6 June 2013
Abstract: In the Sudano-Sahelian areas of Africa droughts can have serious impacts on natural resources, and therefore land surface moisture is an important factor. Insufficient conventional sites for monitoring land surface moisture make the use of Earth Observation data for this purpose a key issue. In this study we explored the potential of using reflectance data in the Red, Near Infrared (NIR), and Shortwave Infrared (SWIR) spectral regions for detecting short term variations in land surface moisture in the Sahel, by analyzing data from three test sites and observations from the geostationary Meteosat Second Generation (MSG) satellite. We focused on responses in surface reflectance to soil- and surface moisture for bare soil and early to mid- growing season. A method for implementing detrended time series of the Shortwave Infrared Water Stress Index (SIWSI) is examined for detecting variations in vegetation moisture status, and is compared to detrended time series of the Normalized Difference Vegetation Index (NDVI). It was found that when plant available water is low, the SIWSI anomalies increase over time, while the NDVI anomalies decrease over time, but less systematically. Therefore SIWSI may carry important complementary information to NDVI in terms of vegetation water status, and can provide this information with the unique combination of temporal and spatial resolution from optical geostationary observations over Sahel. However, the relation between SIWSI anomalies and periods of water stress were not found to be sufficiently robust to be used for water stress detection.
Keywords: soil moisture; vegetation; water stress; Earth observation; MSG SEVIRI; SIWSI; NDVI; Sahel; drought
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Olsen, J.L.; Ceccato, P.; Proud, S.R.; Fensholt, R.; Grippa, M.; Mougin, E.; Ardö, J.; Sandholt, I. Relation between Seasonally Detrended Shortwave Infrared Reflectance Data and Land Surface Moisture in Semi‑Arid Sahel. Remote Sens. 2013, 5, 2898-2927.
Olsen JL, Ceccato P, Proud SR, Fensholt R, Grippa M, Mougin E, Ardö J, Sandholt I. Relation between Seasonally Detrended Shortwave Infrared Reflectance Data and Land Surface Moisture in Semi‑Arid Sahel. Remote Sensing. 2013; 5(6):2898-2927.
Olsen, Jørgen L.; Ceccato, Pietro; Proud, Simon R.; Fensholt, Rasmus; Grippa, Manuela; Mougin, Eric; Ardö, Jonas; Sandholt, Inge. 2013. "Relation between Seasonally Detrended Shortwave Infrared Reflectance Data and Land Surface Moisture in Semi‑Arid Sahel." Remote Sens. 5, no. 6: 2898-2927.