Monitoring changes in biodiversity over Canada during the past three decades using a dynamic habitat index derived from a long-term AVHRR record

Understanding the drivers of biodiversity and establishing methods for biodiversity monitoring and conservation has gained increasing importance over the past decade, with particular focus in 2010, proclaimed by the United Nations to be the International Year of Biodiversity. In this context, satellite remote sensing can provide broad-scale information on a range of geophysical variables such as fraction of photosynthetically active radiation (fPAR) absorbed by a vegetated canopy, or land cover, both of which have been shown to be useful indirect indicators of biodiversity through a connection to species abundance and richness. One satellite-derived indirect indicator of species diversity is the Dynamic Habitat Index (DHI), which combines the cumulative annual fPAR, providing an indication of overall site greenness, the minimum annual apparent fPAR, indicating the base level of vegetation cover observed at a location, and the variation of fPAR (seasonality), estimated as the coefficient of variation. To date the application of the DHI has been restricted to data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors from 2000 onwards. To obtain a longer term time series and earlier baseline of DHI conditions across Canada utilization of the archive of historical satellite data from the Advanced Very High Resolution Radiometer (AVHRR) sensor is proposed. In this paper we will discuss the reprocessing of the 1 km spatial resolution AVHRR archive (1981-2007) using a recently developed processing system, Canadian AVHRR Processing System (CAPS). The CAPS produces multi-date composites that satisfy the geolocation requirements defined by the Global Climate Observing System (GCOS). For the compositing process, a cloud contamination index as well as information on the view zenith angle and cloud shadows is incorporated, and observations are constrained to either the forward or backward scattering hemisphere to reduce Bidirectional Reflectance Distribution Function (BRDF) effects. Using the processed AVHRR data we will compare and contrast differences in the DHI derived from AVHRR and MODIS data post-2000. Once confidence in the AVHRR derived estimates is demonstrated the departures of the annual DHI from the long-term mean are assessed. They are indicative of regions undergoing disturbances or recovery events - information which serves as important indicators of potential changes in species composition and diversity within a given area. An understanding of the relationship between overlapping dates of AVHRR and MODIS DHI values will enable the development of a long time series of DHI values.