<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi All,<div><br></div><div>Currently trying to do some atmospheric corrections on some Landsat 7 and ASTER images to compare forest cover over two time points. I am thinking of using the GRASS <span class="Apple-style-span" style="font-family: arial, sans-serif; ">i.atcorr function, which seems relatively straight forward. Unfortunately I do not have the the visibility [km] for the scenes. Is there a way of calculating these from the images? Are there any tables that one can look up, which contain approximate visibility ranges for "very hazy", "moderately hazy" or "low hazy" conditions? Or simply, is there a better, and easier way of doing these corrections?</span></div><div><font class="Apple-style-span" face="arial, sans-serif"><br></font></div><div><font class="Apple-style-span" face="arial, sans-serif">I would welcome any ideas or suggestions that people might have,</font></div><div><font class="Apple-style-span" face="arial, sans-serif"><br></font></div><div><font class="Apple-style-span" face="arial, sans-serif"><br></font></div><div><font class="Apple-style-span" face="arial, sans-serif">Best</font></div><div><font class="Apple-style-span" face="arial, sans-serif"><br></font></div><div><font class="Apple-style-span" face="arial, sans-serif">Johan</font></div><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="Apple-interchange-newline">--------------------------</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><b>Dr. Johan Oldekop</b></span></font></div><div><font class="Apple-style-span" color="#565656" face="'Helvetica Neue'"><b><font class="Apple-style-span" color="#000000" face="Helvetica"><br></font></b></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Post-Doctoral Research Associate</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">School of Environment</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">W</font></span></font><span class="Apple-style-span" style="color: rgb(124, 124, 124); font-family: HelveticaNeue-Light; font-size: 12px; ">ashington State University</span></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Salmon Creek Avenue</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Vancouver, WA 98686</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">USA</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C"><br></font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C"><span class="Apple-style-span" style="color: rgb(0, 0, 0); ">T: +1 (360) 836 7567 </span></font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C"><span class="Apple-style-span" style="color: rgb(0, 0, 0); ">E: <a href="mailto:j.oldekop@wsu.edu">j.oldekop@wsu.edu</a></span></font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C"><span class="Apple-style-span" style="color: rgb(0, 0, 0); "><br></span></font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Visiting Scientist</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Faculty of Life Sciences</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">The University of Manchester</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Michael Smith Building</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Oxford Road</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">Manchester, M13 9PL</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><font class="Apple-style-span" color="#7C7C7C">UK</font></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br></span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light" size="3"><span class="Apple-style-span" style="font-size: 12px; ">T: +44 (0) 7984 771405</span></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light"><br></font></div><div><font class="Apple-style-span" face="HelveticaNeue-Light"><a href="http://www.madasascientist.com/">www.madasascientist.com</a></font></div></span></div></span></div></span></span>
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