Relationship between biophysical parameters and synthetic indices derived from hyperspectral field data in a salt marsh from Buenos Aires Province; Argentina

Abstract

Remote sensing tools allow the environmentalevaluation of coastal wetlands at a landscape scale; but adeeper understanding is needed of the interactions betweenbiophysical parameters and the electromagnetic signal. Thegoal of this work was to analyze and quantify the influenceof the aboveground biomass and the Leaf Area Index (LAI) onthe spectral response of Spartina densiflora marshes in MarChiquita coastal lagoon; Argentina. Spectral reflectance athigh resolution was measured in S. densiflora canopies undernatural conditions; manipulating standing crop by means ofsuccessive harvest. Reflectance data were acquired using aspectroradiometer in visible; near infrared (IR) and shortwaveIR bands. Spectral Vegetation Indices (VI) were calculated foreach standing crop-LAI situation. Several VI significantly correlatedwith standing crop and LAI; including indices 1) basedon the red-IR edge (IR Index (IRI); 695/760 ratio; Simple Ratio(SR); Red Edge Inflection Point (REIP); and different variationsof the Normalized Difference VI (NDVI Rouse; NDVI amber;NDVI NOAA; NDVI Landsat; NDVI Modis); 2) indices basedon the sharp change green-IR (green NDVI (GNDVI); 800/550ratio) and 3) indices with a correction for soil noise (OSAVI Optimized Soil Adjusted VI (OSAVI); and Modified SAVI(MSAVI). The indices with significant regressions with standingcrop and LAI were IRI; NDVIAmber and REIP. The total andgreen standing crop showed better adjustments than LAI; showingR2 values of 0.5. These values were obtained withREIP index. Results indicate that LAI and standing cropof S. densiflora stands could be determined from spectral databut estimations should be taken carefully in high biomassscenarios; because of indexes saturation at higher LAI values.