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DO ADDITIONAL BANDS (COASTAL, NIR-2, RED-EDGE AND YELLOW) IN 
WORLDVIEW-2 MULTISPECTRAL IMAGERY IMPROVE DISCRIMINATION OF 
AN INVASIVE TUSSOCK, BUFFEL GRASS (CENCHRUS CILIARIS)? 
Victoria Marshall **, Megan Lewis *, Bertram Ostendorf * 
? School of Earth and Environmental Sciences, The University of Adelaide, POB 1 Glen Osmond 5064, South Australia 
(firstname.lastname@adelaide.edu.au ) 
Commission VIII, WG VIII/6 
KEY WORDS: Vegetation, Mapping, Classification, Targets, Multispectral 
ABSTRACT: 
Our goals is to determine if Worldview-2 8-band multispectral imagery can be used to discriminate an invasive grass species 
namely, Buffel grass (Cenchrus ciliaris) in the subtropical arid parts of central Australia and whether it offers a tangible 
improvement on 4-band (visible and near infra red) multispectral imagery. A Worldview-2 scene was acquired for a 
10*10km area just west of Alice Springs in central Australia following heavy rains of early Summer. Mixture Tuned 
Matched Filtering was used to classify the image. Target and 
from the image. Linear discriminate analysis (LDA) was us 
target/ background spectra. The importance of the additiona 
background spectra were selected in the field and extracted 
d to examine the spectral separability of each group of the 
1 spectral bands on the image classification was assessed by 
running LDA for both 8 and 4 bands (red, green, blue and NIR). LDA did not indicate improved separability between 
groups when additional spectral bands were applied. Preliminary classification results indicate that Buffel grass (Cenchrus 
ciliaris) is detected with an omission error 44%, commission error of 11.8% and overall accuracy of 59.5%. We were 
surprised that the additional spectral bands did not improve spectral separability and in part attribute this to the high degree 
of variance we observed within groups of spectra, which was particularly observable in the NIR2 and Yellow bands. The 
analyses may be significantly improved by acquiring imagery following the first big rains at the end of the dry season. At 
this time, phonological differences between our focal species and the surrounding native vegetation should be maximised. 
We suspect that Worldview-2 will offer even greater potential for the discrimination of Buffel grass under these conditions, 
being able to fully utilise the yellow-band in particular. 
1. INTRODUCTION 
Grass invasions represent a significant threat to 
biodiversity and in their aggregate may impact global 
aspects of ecosystem function (D'antonio and Vitousek, 
1992). This is largely due to their impact on native 
wildfire regimes which typically increase in frequency 
and intensity where grass was previously absent. Early 
detection of new invasions fronts is critical for effective 
control. Remote sensing presents as an ideal mode for 
mapping and monitoring invasion as it affords a 
landscape scale view of the invasion and can be cost 
effective compared with laborious field work. However, 
due to the often indistinct spectra of grasses and varying 
sizes of stands, accurate detection using remote sensing 
is challenging. It requires careful consideration of the 
species distinctive features, smallest unit of invasion, 
seasonal growth, and habit as well as characteristics of 
the sensor employed. 
Although successfully applied to  species-level 
discrimination where the target-species covered a broad 
extent and possessed distinct phonological characteristics 
(Arzandeh and Wang, 2003), aerial photography as well 
as long-established multispectral sensors such as Landsat 
and SPOT have been described as inadequate for 
discriminating between grasses (Gray et al., 2008, Stitt et 
al., 2006). Hyperspectral sensors have been proven to 
deliver a high degree of accuracy for species-level 
discrimination (Gray et al., 2009, Lass et al., 2002) but 
the advantages of hyperspectral sensors do not always 
justify the high cost and large volumes of redundant data 
requiring expert interpretation; as a result it is impractical 
for most weed management authorities to utilise this 
imagery. The recently launched (January 2010) Digital 
Globe Sensor Worldview-2 offers a middle ground 
between high spatial and high spectral resolution which 
has been lacking. It provides high spatial resolution (2 m 
multispectral, 0.5 m pan-sharpened) as well as 8 spectral 
bands specifically: short-wave blue (427-458 nm), blue 
(478- 515 nm), green (546- 586 nm), yellow (608- 632 
nm), red (659- 694 nm), red-edge (724- 749 nm), NIR-1 
(833- 901 nm) and NIR-2 (949- 1043 nm). Our aim is to 
determine if Worldview-2 imagery can be used to 
discriminate an invasive grass species namely, Buffel 
grass (Cenchrus ciliaris) in the subtropical arid parts of 
central Australia and whether it offers a tangible 
improvement on 4-band (visible and near infra red) 
multispectral imagery.