Seasonal persistent green cover is derived from seasonal fractional cover using a weighted smooth spline fitting routine. This weights a smooth line to the minimum values of the seasonal green cover. This smooth minimum is designed to represent the slower changing green component, ideally consisting of perennial vegetation including over-storey, mid-storey and persistent ground cover. The seasonal persistent green is then summarized using simple linear regression, and the slope of the fitted line is captured in this product. The original units are percentage points per year. Values are later truncated and scaled.
Credit
We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
This dataset was produced in partnership with the Joint Remote Sensing Research Program using Landsat 5 TM, Landsat 7 ETM+ and Landsat 8 OLI satellite data sourced from the US Geological Survey.
Purpose
The trends in persistent green are considered to be indicators of change in woody vegetation cover. This linear seasonal persistent green trend product largely shows the effect of climate and rainfall on woody vegetation. To examine trends adjusted for rainfall, use the climate adjusted linear seasonal persistent green trend product.
Supplemental Information
Filenames for the seasonal fractional cover product conforms to the AusCover standard naming convention. The standard form of this convention is:
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For more information, see the file naming convention file provided with this dataset.
Lineage
Data Creation
Persistent Green Fractional Cover:
Smoothing splines are fitted in multiple iterations per pixel through the full time series of seasonal fractional cover (green fraction only). At each iteration, zero weight is given to observations that lie above the spline, and observation below the line are weighted proportion to the size of the residual. Observations greater than 3 standard deviations from the residual mean are given zero weight, and those between 2 and 3 standard deviations are given less weight, this avoids contamination by outliers. Persistent green fractional cover for each season is estimated from the final spline iteration at each seasonal time step. Values reported are as for fractional cover, ie. percentages of cover plus 100. Areas with frequent seasonal fractional cover data gaps due to cloud may produce unreliable estimates of persistent green cover.
Linear Seasonal Persistent Green Trend:
The seasonal persistent green product is summarised using simple linear regression, and the slope of the fitted line is captured in this product. The original units are percentage points per year. Values are later truncated and scaled.
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