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| <h2>DESCRIPTION</h2> | ||
| <em>i.sentinel.preproc</em> allows to download, import and apply atmospheric correction to Sentinel 2 images. | ||
| <!--p> | ||
| The implemented procedure consists essentially of values thresholds, comparisons and calculations between bands and they lead to two different | ||
| rough maps of clouds and shadows which require further improvements and elaborations (e.g. transformation from raster to vector, cleaning geometries, | ||
| removing small areas, checking topology, etc.) carried out in the different steps of the procedure. | ||
| <table cellspacing="2" cellpadding="2" width="100%" border="0"> | ||
| <tbody> | ||
| <tr> | ||
| <td align="center" valign="bottom"><a href="i_sentinel_mask_GWF.png"><img src="i_sentinel_mask_GWF.png" width="100%"></a><br><i>Fig: Module General WorkFlow</i></td> | ||
| <td align="center" valign="bottom"><a href="i_sentinel_mask_CD.png"><img src="i_sentinel_mask_CD.png" width="100%"></a><br><i>Fig: Cloud detection procedure</i></td> | ||
| <td align="center" valign="bottom"><a href="i_sentinel_mask_SD.png"><img src="i_sentinel_mask_SD.png" width="100%"></a><br><i>Fig: Shadow detection procedure</i></td> | ||
| </tr> | ||
| </tbody> | ||
| </table> | ||
| <p> | ||
| The algorithm has been developed starting from rules found in literature (Parmes et. al 2017) and conveniently refined.<br> | ||
| Regarding the detection of shadows, some misclassification can occur. Often shadows and water have in fact similar reflectance | ||
| values which can lead to erroneous classification of water bodies as shadows. Therefore, in order to increase the accuracy of | ||
| the final shadow mask, a control check is implemented. Clouds and shadows are spatially intersected in order to remove misclassified areas. | ||
| This means that all those shadow geometries which do not intersect a cloud geometry are removed. | ||
| <div align="center" style="margin: 10px"> | ||
| <a href="i_sentinel_mask_CS.png"> | ||
| <img src="i_sentinel_mask_CS.png" width="30%"> | ||
| </a><br> | ||
| <i>Fig: Module General WorkFlow</i> | ||
| </div--> | ||
| <!--center> | ||
| <img src="i_sentinel_mask_CS.png" width="30%"> | ||
| <br> | ||
| <i>Fig: Module General WorkFlow</i> | ||
| </center--> | ||
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| <!--p> | ||
| All necessary input bands (blue, green, red, nir, nir8a, swir11, swir12) must be imported in GRASS and specified one by one or using a text file. | ||
| The text file has to be written following the syntax below: <em>variable=your_map</em> | ||
| <div class="code"><pre> | ||
| blue=<em>your_blue_map</em> | ||
| green=<em>your_green_map</em> | ||
| red=<em>your_red_map</em> | ||
| nir=<em>your_nir_map</em> | ||
| nir8a=<em>your_nir8a_map</em> | ||
| swir11=<em>your_swir11_map</em> | ||
| swir12=<em>your_swir12_map</em> | ||
| </pre></div> | ||
| Tha variables names (blue, green, red, nir, nir8a, swir11, swir12) have to be written precisely like in the example above (e.g. not Blue, nor BLUE but blue), | ||
| no spaces or special characters are permitted. | ||
| <p> | ||
| The final outputs are two different vector maps, one for clouds and one for shadows. | ||
| <p> | ||
| The metadata file (MTD_TL.xml) is required only if both masks (cloud and shadow) | ||
| are computed. The module retrieves from this file the sun azimuth and zenith necessary for the shadow mask cleaning phase | ||
| <em>(see the schema above)</em> | ||
| <p> | ||
| If flag <b>-s</b> is given all selected bands are rescaled using the specified scale factor [<b>scale_fac</b>=<em>integer</em>]. By default the scale factor is set to 10000, | ||
| the QUANTIFICATION_VALUE from the metadata of Sentinel 2 images. | ||
| <p> | ||
| The module takes the current region settings into accout. To ignore the current region and set it from the whole image, the flag <b>-r</b> has to be given. | ||
| <p> | ||
| The module allows to compute only the cloud mask or both cloud and shadow masks. If flag <b>-c</b> is given, only the cloud procedure will be performed. The computation | ||
| of cloud mask is mandatory for shadow mask creation. In fact cloud map is used during the cleaning phase of the shadow mask in order to remove misclassifications.<--> | ||
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| <h2>EXAMPLE</h2> | ||
| <!--div class="code"> | ||
| i.sentinel.mask -r -s input_file=/home/input_bands.txt cloud_mask=cloud_sen2 shadow_mask=shadow_sen2 mtd_file=/home/MTD_TL.xml scale_fac=1000 | ||
| </div> | ||
| <p> | ||
| -r to set the computational region to the maximum image extente and -s to rescale the input bands with the specified scale factor (in this case 1000) | ||
| <h2>REFERENCE</h2> | ||
| <ul> | ||
| <li>Parmes et. al 2017</li> | ||
| </ul--> | ||
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| <h2>SEE ALSO</h2> | ||
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| <em> | ||
| <a href="i.sentinel.download.html">i.sentinel.download</a>, | ||
| <a href="i.sentinel.import.html">i.sentinel.import</a>, | ||
| <a href="i.sentinel.import.html">i.atcorr</a>, | ||
| <a href="i.sentinel.import.html">i.sentinel.mask</a>, | ||
| <a href="r.import.html">r.import</a>, | ||
| <a href="r.extenal.html">r.external</a> | ||
| </em> | ||
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| <h2>AUTHOR</h2> | ||
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| Roberta Fagandini, GSoC 2018 student<br> | ||
| <a href="https://wiki.osgeo.org/wiki/User:Mlennert">Moritz Lennert</a><br> | ||
| <a href="https://wiki.osgeo.org/wiki/User:Robertomarzocchi">Roberto Marzocchi</a> |