Wind Erosion in Western Queensland Australia

Chapter 6 – Field Assessments and Model Validationstamp, position (latitude, longitude), positional accuracy and number of satellites for theposition reading, followed by the conditional assessments.6.2.3 Calibration of ObservationsA trial survey of 168 observations in May 2006 was used to test the assessment procedureand refine the methodology. Calibration of the vegetation cover estimates was performed bycomparison of visual estimates with data collected using a point-intercept transect survey(after Hassett, 2006). Six calibration sites were established across the study area (Figure 6.1).Calibration data were collected at each site in October 2005, September 2006, November2006 and May 2007. Six 250 m transects were run at 60° intervals radiating from a fixedcentral point at each site. Observations of plant (lower and upper stratum) and plant litterpresence/absence were recorded at 2 m intervals along the transects. The cover fraction ofplant litter and herbaceous and woody vegetation were computed by dividing the number ofrecords for each cover type by the total number of observation points per site (750). Visualassessments of cover made at the sites prior to the surveys were then compared with recordedcover fractions (Figure 6.2). Good agreement was found between observed and measuredgrass cover (r 2 = 0.85). The regression equation (Figure 6.2) was used to calibrate the visualcover assessments.Figure 6.2 Calibration regression of field estimates of herbaceous vegetation cover versus recordedcover based on 24 calibration tests (October 2005 to May 2007).161