Monitoring Vegetation Moisture Using Passive Microwave and Optical Indices in the Dry Chaco Forest, Argentina

VERÓNICA BARRAZA; FRANCISCO GRINGS; PAOLO FERRAZOLI; MERCEDES SALVIA; MARTÍN MAAS; RASHID RAHMOUNE; CRISTINA VITTUCCI; HAYDEE KARSZENBAUM

IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Lugar: New York; Año: 2014 vol. 7 p. 421 - 430

1939-1404

Information about daily variations of vegetationmoisture is of widespread interest to monitor vegetation stress andas a proxy to evapotranspiration. In this context, we evaluated opticaland passive microwave remote sensing indices for estimatingvegetation moisture content in the Dry Chaco Forest, Argentina.The three optical indices analyzed were the Normalized DifferenceVegetation Index (NDVI), the Normalized Difference Water Index(NDWI) and the Normalized Difference Infrared Index (NDII)and, for the microwave region the Frequency Index (FI). All theseindices are mainly sensitive to leaf area index (LAI), but NDWIand NDII, and FI are also sensitive to leaf water content (LWC)and Canopy Water Content (CWC) respectively. Using optical andmicrowave radiative transfer models for the vegetation canopy,we estimated the range of values of LAI, LWC and CWC thatcan explain both NDWI/NDII and FI observations. Using a combinationof simulations and microwave and optical observations,we proposed a two step approach to estimate leaf and canopymoisture content from NDWI, NDII and FI. We found that theshort variation of LWC estimated from NDWI and NDII presenta dynamic range of values which is difficult to explain from thebiophysical point of view, and it is partially related to atmospherecontamination and canopy radiative transfer model limitations.Furthermore, the observed FI short-term variations ( 8 days)cannot be explained unless significant CWC variations are assumed.The CWC values estimated from FI present a short-termvariations possibly related to vegetation hydric stress.