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109<br />

Test Site<br />

Figure 2. Variation of SWE for winter se<strong>as</strong>on 2003–2004 <strong>an</strong>d <strong>the</strong> corresponding Box plot<br />

In this study we verify <strong>the</strong> correlation between SSM/I ch<strong>an</strong>nels <strong>an</strong>d snow depth <strong>an</strong>d SWE for<br />

different types of l<strong>an</strong>d cover located in different latitudes. Three series (2002–2004) of SSM/I<br />

ch<strong>an</strong>nels versus snow depth <strong>an</strong>d SWE for each of <strong>the</strong> selected sites were derived. The SSM/I data<br />

were obtained from <strong>the</strong> descending p<strong>as</strong>s of Defense Meteorological Satellite Program (DMSP)<br />

satellites. There are three SSM/I scattering signatures used in this <strong>an</strong>alysis. The first scattering<br />

signature named GTH (19H–37H) is <strong>the</strong> difference between 19 <strong>an</strong>d 37 GHz in horizontal<br />

polarization. The second signature, GTVN (19V–37V) shows <strong>the</strong> discrep<strong>an</strong>cy between vertically<br />

polarized 19 <strong>an</strong>d 37 GHz. Finally, SSI (22V–85V) presents <strong>the</strong> difference between 22 <strong>an</strong>d 85 GHz<br />

in vertical polarization. SSI c<strong>an</strong> be used to identify shallow snowcover. The Box plot of <strong>the</strong><br />

signatures GTH <strong>an</strong>d GTVN for winter se<strong>as</strong>on 2003–2004 is shown in figure 3. The outliers in <strong>the</strong><br />

Box plots r<strong>an</strong>ge from –20 to 20 are due to ei<strong>the</strong>r sensor or data processing errors which need to be<br />

eliminated. GTVN me<strong>an</strong> r<strong>an</strong>ges from 5 to 15 for all <strong>the</strong> pixels except for <strong>the</strong> test site 12 which is<br />

very close to <strong>the</strong> lake. GTH Box plot <strong>an</strong>d me<strong>an</strong> h<strong>as</strong> <strong>the</strong> same pattern <strong>as</strong> GTVN. The test site 12 h<strong>as</strong><br />

a me<strong>an</strong> around –5 for GTVN (19V–37V) indicating of <strong>the</strong> fact that part of SSM/I pixel is water.<br />

Since <strong>the</strong> SSM/I sensor have different spatial resolution for various ch<strong>an</strong>nel, <strong>the</strong> scattering from<br />

pixel 12 is disturbed in ch<strong>an</strong>nel 19GHz (69km resolution) by <strong>the</strong> lake however it is not disturbed<br />

in ch<strong>an</strong>nel 37GHz (37km resolution). The low scattering of <strong>the</strong> water <strong>an</strong>d high scattering of <strong>the</strong><br />

l<strong>an</strong>d make <strong>the</strong> difference of 19V–37V a negative number.<br />

GTVN (19H-37H) (k)<br />

Box Plot of GTVN for Points 1-19 Box Plot of GTH for Points 1-19<br />

Test Site<br />

GTH (19H-37H) (k)<br />

Test site<br />

Figure 3. Box-Whiskers plot of GTVN <strong>an</strong>d GTH for winter se<strong>as</strong>on 2003–2004

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