A comparative study of satellite and ground-based phenology

Abstract

Long time series of ground-based plant phenology, as well as more than two decades of satellite-derived phenological metrics, are currently available to assess the impacts of climate variability and trends on terrestrial vegetation. Traditional plant phenology provides very accurate information on individual plant species, but with limited spatial coverage. Satellite phenology allows monitoring of terrestrial vegetation on a global scale and provides an integrative view at the landscape level. Linking the strengths of both methodologies has high potential value for climate impact studies. We compared a multispecies index from ground-observed spring phases with two types (maximum slope and threshold approach) of satellite-derived start-of-season (SOS) metrics. We focus on Switzerland from 1982 to 2001 and show that temporal and spatial variability of the multispecies index correspond well with the satellite-derived metrics. All phenological metrics correlate with temperature anomalies as expected. The slope approach proved to deviate strongly from the temporal development of the ground observations as well as from the threshold-defined SOS satellite measure. The slope spring indicator is considered to indicate a different stage in vegetation development and is therefore less suited as a SOS parameter for comparative studies in relation to ground-observed phenology. Satellite-derived metrics are, however, very susceptible to snow cover, and it is suggested that this snow cover should be better accounted for by the use of newer satellite sensors.

An overview of recent remote sensing and GIS based research in ecological informatics

“…Many studies have exploited the temporal dimension of remote sensing, a valuable attribute for studies of ecological systems, notably as a source of information on variables such as the timing and monitoring of vegetative phenological events . Satellite remote sensing has become increasingly important in studies of phenological change at landscape to global scales (Studer et al, 2007;Motohka et al, 2009;Julien and Sobrino, 2009), particularly now the satellite record is over thirty years old, providing a means to help study impacts of environmental change. Vegetative phenological events are, for example, useful indictaors of the impact of climate change in the terrestrial biosphere (Brügger et al, 2003).…”

Using digital time-lapse cameras to monitor species-specific understorey and overstorey phenology in support of wildlife habitat assessment

“…Time series of phenology data can be developed using single or multiple observers at single locations, or through phenological networks, where multiple observers record observations of the same species at different locations (Bertin 2008). At broad spatial scales, satellite imagery, such as the normalized difference vegetation index, based on the normalized spectral reflectance in the red and near infrared regions of the electromagnetic spectrum, has been used for documenting patterns of 'leafing out' in spring (Botta et al 2000;Studer et al 2007). There are limitations, however, related to the broad spatial resolution of these sensors, which can be further exacerbated by poor temporal resolution in areas with persistent cloud cover.…”

“…There are limitations, however, related to the broad spatial resolution of these sensors, which can be further exacerbated by poor temporal resolution in areas with persistent cloud cover. Other issues concerning satellite measurements are the need for adjustments due to changes in orbital and atmospheric conditions, and possible influences of late snow cover on the resultant data (Schwartz and Reed 1999;Studer et al 2007).…”

Temporal variations in phenological events of forests, grasslands and desert steppe ecosystems in Mongolia: a remote sensing approach

“…According to the modified threshold method (Piao et al 2006), the OG and OD is diagnosed at the inflection point (a specific date) of the curve of serial vegetation index when it begins to ascend or descend in a year duration. This method was furthermore found to be more sensitive to climate change (Jeong et al 2011, Shen et al 2011, highly correlated with a ground observed phenology index (Studer et al 2007) and presumably reduced climatic impacts such as aerosols, clouds, disturbances, and defoliation on annual values (Jeong et al 2011).…”