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<p class="MsoNormal">G’day list,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m calculating cross-variograms (variables below are sumso2=”sulphur dioxide emissions” and intensity=”rain intensity” – I have 2500 sample points) using GSTAT in R:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">g <- gstat(NULL, id = "sumso2", form = sumso2 ~ 1, data=d1)<o:p></o:p></p>
<p class="MsoNormal">g <- gstat(g, id = "intensity", form = intensity ~ 1, data=d1)<o:p></o:p></p>
<p class="MsoNormal">d1xv.so2Vin <- variogram(g, cutoff=0.3, width=0.01)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">but - just looking at the variogram for sumso2 alone after this process (d1so.png):<o:p></o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU"><img width="325" height="225" id="Picture_x0020_4" src="cid:image002.png@01CD6345.4D6377B0"></span><o:p></o:p></p>
<p class="MsoNormal">The sumso2 semi-variogram has a trend – and I need to remove it.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">If I calculate the variance of each point from the overall mean squared – and use that as sumso2 in the same gstat process – I get the sumso2 semi-variogram as (d1sores.png):<o:p></o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU"><img width="325" height="225" id="Picture_x0020_3" src="cid:image003.png@01CD6343.D40EC9B0"></span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is a better semi-variogram – not ideal yet – but better.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My question is – is that calculation using the mean noted above suitable for removing the trend sufficient for ensuring a suitable cross-variogram? Note – I don’t need to fit models or go to co-kriging – I’m just examining the form of the
spatial relationships – I just want to describe the variable relationships as shown in the cross-variogram (a geography project).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now – if this is not suitable for removing the trend – then I understand I need to fit a polynomial to the variable sumso2 – could someone describe how I can do that it gstat please?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My substantial thanks,<o:p></o:p></p>
<p class="MsoNormal"><b><i><span style="mso-fareast-language:EN-AU">________________________________________________________<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="mso-fareast-language:EN-AU">Michael Hewson
</span></i></b><i><span style="font-size:10.0pt;mso-fareast-language:EN-AU">PhD candidate<o:p></o:p></span></i></p>
<p class="MsoNormal"><span style="font-size:10.0pt;mso-fareast-language:EN-AU"><a href="http://www.gpem.uq.edu.au/crg"><span style="color:blue">Climate Research Group</span></a> |
<a href="http://www.gpem.uq.edu.au/cser"><span style="color:blue">Centre for Spatial Environmental Research</span></a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;mso-fareast-language:EN-AU">The University of Queensland | Brisbane Q 4072 | Australia<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;mso-fareast-language:EN-AU">m.hewson@uq.edu.au |
<b><i>+61 (0)408 379 373<o:p></o:p></i></b></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;mso-fareast-language:EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU"><img border="0" width="447" height="55" id="Picture_x0020_1" src="cid:image001.jpg@01CD6343.0CCCA7F0" alt="Description: ClimateResearchGroupbanner"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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