Determination of phenological dates in boreal regions using normalized difference water index

Abstract

Monitoring and understanding plant phenology are important in the context of studies of terrestrial productivity and global change. Vegetation phenology, such as dates of onsets of greening up and leaf senescence, has been determined by remote sensing using mainly the normalized difference vegetation index (NDVI). In boreal regions, the results suffer from significant uncertainties because of the effect of snow on NDVI. In this paper, SPOT VEGETATION S10 data over Siberia have been analysed to define a more appropriate method. The analysis of time series of NDVI, normalized difference snow index (NDSI), and normalized difference water index (NDWI), together with an analysis of in situ phenological records in Siberia, shows that the vegetation phenology can be detected using NDWI, with small effect of snow. In spring, the date of onset of greening up is taken as the date at which NDWI starts increasing, since NDWI decreases with snowmelt and increases with greening up. In the fall, the date of onset of leaf coloring is taken as the date at which NDWI starts decreasing, since NDWI decreases with senescence and increases with snow accumulation. The results are compared to the results obtained using NDVI-based methods, taking in situ phenological records as the reference. NDWI gives better estimations of the start of greening up than NDVI (reduced RMSE, bias and dispersions, and higher correlation), whereas it does not improve the determination of the start of leaf coloring. A map of greening up dates in central Siberia obtained from NDWI is shown for year 2002 and the reliability of the method is discussed. D

Applicability of Green-Red Vegetation Index for Remote Sensing of Vegetation Phenology

“…Therefore, NDVI cannot clearly discriminate the growing period from other conditions with a simple site-independent single threshold. We must consider the presence or absence of snow/water cover and understory vegetation for each target when we use NDVI, as pointed out by several studies [24][25][26][27]. Furthermore, as Nagai et al [13] have reported, the canopy condition of autumn coloring corresponded to different NDVI values from year to year.…”

Ndwi-Based Technique for Detection of Change Dates of the Growing Seasons in Russian Subarctic

“…The graphs reflect correspondence between the ground and satellite observations. Some authors describe a possibility of allocation of the framing dates for full growing season through the allocation of the two corresponding minimums on the graphs (Delbart et al, 2005;Sekhon et al, 2010;Semenova, 2015). However, their publications are not cover the issue of separation of the full growing season into spring, summer and autumn.…”

Long-Term Detection of Global Vegetation Phenology from Satellite Instruments

“…To reduce snow contamination, which generally results in a dramatically steep drop in NDVI and irregular variation in EVI , snow cover observations are explicitly removed or replaced. This is done using nearest non-snow observations in a temporal VI trajectory after winter periods are determined using ancillary data of land surface temperature and snow detection (Zhang et al, 2004a;Tan et al, 2011) or high values of NDWI (Delbart et al, 2005).…”

“…The commonly used methods are the threshold-based technique which is divided into absolute VI threshold (e.g., Lloyd, 1990;Fischer, 1994;Myneni et al, 1997;Zhou et al, 2001) and relative threshold (e.g., White et al, 1997;Jonsson and Eklundh, 2002;Delbart et al, 2005;Karlsen et al, 2006;Dash et al, 2010), moving average (Reed et al, 1994), spectral analysis (Jakubauskas et al, 2001;Moody and Johnson, 2001), and inflection point estimation in the time series of vegetation indices (Moulin et al 1997;Zhang et al 2003;Tan et al, 2011). Various approaches in detecting phenological timing, particularly the greenup onset, are compared using the same dataset (de Beurs and Henebry, 2010;White et al, 2009).…”

“…These include Normalized Difference Water Index (NDWI) (Delbart et al, 2005), FPAR (Verstraete et al, 2008), and LAI (Obrist et al, 2003).…”