| 09 Nov 2015 12:38 AM |
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<p>I have converted a set of ASTER level 1b data to reflectance using FLAASH algorithm. After reflectance conversion I am getting anomalous high value for band 9 for each and every pixel. Band statistics of both radiance and reflectance data have given bellow. Please help me to locate the problem. </p>
<p>Band Statistics of Radiance data</p>
<table border="0" cellpadding="0" cellspacing="0" width="384" style="border-collapse: collapse; width: 288pt;">
<colgroup><col width="64" span="6" style="width: 48pt;" /> </colgroup>
<tbody>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt; width: 48pt;"><span style="background-color: #ffff00;">Basic</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Stats</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Min</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Max</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Mean</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">StdDev</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">1</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">171.704</span></td>
<td align="right"><span style="font-size: 13px;">41.81371</span></td>
<td align="right"><span style="font-size: 13px;">32.52461</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">2</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">179.832</span></td>
<td align="right"><span style="font-size: 13px;">37.17543</span></td>
<td align="right"><span style="font-size: 13px;">30.15347</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">3</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">164.642</span></td>
<td align="right"><span style="font-size: 13px;">43.61517</span></td>
<td align="right"><span style="font-size: 13px;">33.56738</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">4</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">30.436</span></td>
<td align="right"><span style="font-size: 13px;">10.64188</span></td>
<td align="right"><span style="font-size: 13px;">8.533924</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">5</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">13.572</span></td>
<td align="right"><span style="font-size: 13px;">2.812215</span></td>
<td align="right"><span style="font-size: 13px;">2.288882</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">6</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">15.875</span></td>
<td align="right"><span style="font-size: 13px;">2.671873</span></td>
<td align="right"><span style="font-size: 13px;">2.194599</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">7</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">14.8056</span></td>
<td align="right"><span style="font-size: 13px;">2.339734</span></td>
<td align="right"><span style="font-size: 13px;">1.929433</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">8</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">10.5918</span></td>
<td align="right"><span style="font-size: 13px;">1.577551</span></td>
<td align="right"><span style="font-size: 13px;">1.312576</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">9</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">8.077201</span></td>
<td align="right"><span style="font-size: 13px;">1.082738</span></td>
<td align="right"><span style="font-size: 13px;">0.876391</span></td>
</tr>
</tbody>
</table>
<p><br />
</p>
<p>Band statistics of Reflectance data</p>
<table border="0" cellpadding="0" cellspacing="0" width="384" style="border-collapse: collapse; width: 288pt;">
<colgroup><col width="64" span="6" style="width: 48pt;" /> </colgroup>
<tbody>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt; width: 48pt;"><span style="background-color: #ffff00;">Basic</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Stats</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Min</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Max</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">Mean</span></td>
<td style="width: 48pt;"><span style="background-color: #ffff00;">StdDev</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">1</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.4331</span></td>
<td align="right"><span style="font-size: 13px;">0.067378</span></td>
<td align="right"><span style="font-size: 13px;">0.055313</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">2</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.5271</span></td>
<td align="right"><span style="font-size: 13px;">0.08557</span></td>
<td align="right"><span style="font-size: 13px;">0.072677</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">3</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.7011</span></td>
<td align="right"><span style="font-size: 13px;">0.168304</span></td>
<td align="right"><span style="font-size: 13px;">0.130212</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">4</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.5448</span></td>
<td align="right"><span style="font-size: 13px;">0.185556</span></td>
<td align="right"><span style="font-size: 13px;">0.152326</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">5</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.6896</span></td>
<td align="right"><span style="font-size: 13px;">0.13885</span></td>
<td align="right"><span style="font-size: 13px;">0.115235</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">6</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.8506</span></td>
<td align="right"><span style="font-size: 13px;">0.139334</span></td>
<td align="right"><span style="font-size: 13px;">0.11637</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">7</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.8938</span></td>
<td align="right"><span style="font-size: 13px;">0.135989</span></td>
<td align="right"><span style="font-size: 13px;">0.115693</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">8</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">0.9276</span></td>
<td align="right"><span style="font-size: 13px;">0.133352</span></td>
<td align="right"><span style="font-size: 13px;">0.114106</span></td>
</tr>
<tr height="20" style="height: 15pt;">
<td style="height: 15pt;"><span style="font-size: 13px;">Band</span></td>
<td align="right"><span style="font-size: 13px;">9</span></td>
<td align="right"><span style="font-size: 13px;">0</span></td>
<td align="right"><span style="font-size: 13px;">1</span></td>
<td align="right"><span style="font-size: 13px;">0.222092</span></td>
<td align="right"><span style="font-size: 13px;">0.184385</span></td>
</tr>
</tbody>
</table>
<p >Thank You...</p>
<p ><br />
</p>
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Deleted User
Basic Member
Posts:228  
| 11 Nov 2015 03:05 PM |
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<p>I am afraid that I do not understand what you are seeing that leads you to conclude that your reflectance is anomalously high for every pixel in ASTER band 9. In your tables, it looks like the mean reflectance value for Band 9 is about 0.222, which is not a particularly high reflectance value. Are you concerned because your mean radiance values in Band 9 were lower than the mean radiance values for every other band? An atmospheric correctly can change these relationships significantly. In this case, it would mean that the modeled atmosphere indicates that the atmosphere was absorbing a significant amount of the light at the Band 9 wavelengths. When that effect is modeled-out, then the Band 9 values can become higher, relative to the other bands.</p>
<p>- Peg</p>
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Deleted User
New Member
Posts: 
| 16 Nov 2015 01:10 AM |
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<p>Thanks peg for your kind reply... From the statistics of reflectance data it seems to be correct. But when I am going for spectral signature each pixel is showing unexpected peak near band 9. I was interested to share some spectral signature for better understanding but unable to insert here. As the spectral signature is looking quite different from library, I am suspecting that whether the radiance data is correct one or I did any mistake in processing ?</p>
<p>Here is the tabular format of spectral signature </p>
<p> </p>
<table border="0" cellpadding="0" cellspacing="0" width="338" style="border-collapse: collapse; width: 254pt;">
<colgroup><col width="64" style="width: 48pt;" /> <col width="110" style="width: 83pt;" /> <col width="100" style="width: 75pt;" /> <col width="64" style="width: 48pt;" /> </colgroup>
<tbody>
<tr height="20" style="height: 15pt;">
<td class="xl64" style="height: 15pt; width: 48pt;">ASTER</td>
<td class="xl64" style="width: 83pt;">wavelength </td>
<td colspan="2" class="xl65" style="width: 123pt;">Reflectance</td>
</tr>
<tr height="20" style="height: 15pt;">
<td class="xl64" style="height: 15pt;">Bands</td>
<td class="xl65">in µm</td>
<td class="xl65">image derived</td>
<td class="xl65">library</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">1</td>
<td align="right">0.556</td>
<td align="right">0.2624</td>
<td align="right">0.128378</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">2</td>
<td align="right">0.661</td>
<td align="right">0.2813</td>
<td align="right">0.122815</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">3</td>
<td align="right">0.807</td>
<td align="right">0.3029</td>
<td align="right">0.119183</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">4</td>
<td align="right">1.656</td>
<td align="right">0.2228</td>
<td align="right">0.104907</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">5</td>
<td align="right">2.167</td>
<td align="right">0.202</td>
<td align="right">0.095621</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">6</td>
<td align="right">2.209</td>
<td align="right">0.1944</td>
<td align="right">0.094852</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">7</td>
<td align="right">2.262</td>
<td align="right">0.195</td>
<td align="right">0.091977</td>
</tr>
<tr height="20" style="height: 15pt;">
<td align="right" style="height: 15pt;">8</td>
<td align="right">2.336</td>
<td align="right">0.205</td>
<td align="right">0.090249</td>
</tr>
<tr height="20" style="height: 15pt;">
<td class="xl63" align="right" style="height: 15pt;"><span style="background-color: #ffff00;">9</span></td>
<td class="xl63" align="right"><span style="background-color: #ffff00;">2.4</span></td>
<td class="xl63" align="right"><span style="background-color: #ffff00;">0.3586</span></td>
<td class="xl63" align="right"><span style="background-color: #ffff00;">0.092829</span></td>
</tr>
</tbody>
</table>
<p> All other bands are showing acceptable value following the similar pattern as per library spectra, but band 9 is giving quite high value compared to other bands. </p>
<p>Thanks...</p>
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Deleted User
Basic Member
Posts:228
| 16 Nov 2015 01:54 PM |
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<p>I see. My guess is that you have set something in your FLAASH parameters that is causing FLAASH to overcorrect the values in Band 9, relative to the correction applied to other bands. An overcorrection means that the model assumes more atmospheric effects in Band 9 than were really present. So when those non-present effects are "corrected out" you end up with an incorrectly high value in Band 9.</p>
<p>ASTER Band 9 falls just before (and slightly overlapping the edge of) a wide atmospheric absorption band due to atmospheric water and carbon dioxide. It could be that you have provided parameters to FLAASH that indicate more water and CO2 in the atmosphere than there really was at the time the image was taken. In this case, FLAASH removes the effects of the modeled (not the real) atmosphere, which is an overcorrection, leading to higher reflectance values than are valid. </p>
<p>- Peg</p>
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Deleted User
New Member
Posts:
| 16 Nov 2015 10:18 PM |
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<p>Thank you Peg..</p>
<p>I hope your suggestion will help me a lot.</p>
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