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Product pages » Queensland Ground Cover Index

Queensland Ground Cover Index

Last modified by Peter Scarth on 2012/03/24 15:29

Ground Cover Index

Statewide Landcover and Trees Study (SLATS) Bare Ground Index (BGI), Landsat SLATS Scene Series

Overview

Using a multiple regression approach a generalised Bare Ground Index (BGI) that can be applied across large areas with different soil backgrounds has been developed (Scarth et al., 2006). 

The BGI does not require the use of ancillary data for the purpose of stratification of areas into similar units (Scarth et al., 2006).

Future development

Product is deprecated and is currently being replaced by the Fractional Cover product.

Background

Overview

The project Bare Ground Index (BGI) uses Landsat TM and ETM+ satellite imagery acquired from Geoscience Australia. This imagery has a nominal ground resolution of 30 metres. The imagery is converted to reflectance units based on calibration results. It is standardised for atmospheric and directional variations between dates and scenes using an empirical radiometric correction (De Vries, 2004). The analysis has been completed on each of 87 satellite scenes. 

Algorithm

The pixel values in this data set represent the percentage of Bare Ground between 0 and 100%. Conversely, the data can be interpreted as representing Ground Cover between 0 and 100%. For example, where bare ground is quantified as 60% it can be assumed that ground cover is 40% (i.e. 60 + 40 = 100%). Note, however, that the data has been scaled between 100 and 200 in order to allow the zero value to be used for ‘no data.’ Therefore, an image pixel value of 100 equates to 0% Bare Ground and an image pixel value of 200 represents 100% Bare Ground.

Water, topographic shadow, cloud and cloud shadow masks were created for each scene using spectral classification and visual interpretation. Imagery with a file name containing ‘..bi3...’ have no masks applied, while imagery names containing ‘..bi4...’ have masks applied.

The use of multi-date imagery helps remove some of the seasonal effects present in any individual image date and produces a longer-term view of Bare Ground. 

At each field site a range of measurements were taken. Scarth et al. (2006) separates these into two components:

 Collection of discrete point transect sampling data to determine ground cover and the Foliage Projective Cover (FPC) of the over storey and mid storey woody vegetation;

  Description of general site details, including characteristics such as soil and rock hue value and chroma, tree basal area, dominant species, and soil surface characteristics according to the method described by Tongway and Hindley (1995).

The multiple regression approach used to derive the BGI has been field calibrated using approximately 400 Ground Cover sites.

Quality

Quality and limitations

All the data described here has been generated from the analysis of Landsat Thematic Mapper (TM) data, which has a spatial resolution of 30m. The imagery is rectified using control points measured with a differential GPS ensuring a maximum root mean square (RMS) error of 20 metres at these control points. However, it is possible that errors up to ±50 meters occur between these control points. The imagery has been corrected for height displacement using a 3” digital elevation model (DEM) in coastal areas and a 9” DEM for the remainder of the State. It is not recommended that these data sets be used at scales more detailed than 1:100,000.


References

Documentation

De Vries, C., Danaher, T. and Scarth, P., 2004. Calibration of multiple Landsat sensors based on pseudo-invariant target sites in Western Queensland, Australia, International Geoscience and Remote Sensing Symposium (IGARSS), pp. 3729-3732.

Scarth P., Byrne M., Danaher T., Henry B., Hassett R., Carter J., Timmers P. (2006) State of the paddock: monitoring condition and trend in ground cover across Queensland. 13th Australasian Remote Sensing and Photogrammetry Conference, Canberra, Australia, 20 - 24 November 2006. 

Tongway, D. and Hindley, N. 1995. Manual for Assessment of Soil Condition of Tropical Grasslands. Division of Wildlife and Ecology, CSIRO. 1995. ISBN 0 643 05779 X. 

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Created by Ian Grant on 2012/03/11 21:21

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