To improve the definition of useful areas under clouds, it is necessary to detect cloud and shadow in images.
This tool is intended to speed up the cloud and shadow detection process by means of image processing specific techniques applied together and following pre-defined pattern resulting in a vectorial data representing analyzed objects.
Different from other used algorithms to detect such objects, this tool is able to detect this objects in an image of any satellite, not being specific to some sensor type. It is also possible to use some image extension types, such as TIFF, JPEG, etc.
To detect such objects it is necessary to define which image bands will be analyzed, i.e., the analysis is done in distinct bands of the image because each image band has a better response to each spectrum interval. For instance, LANDSAT satellite images have a better definition of high radiance objects such as clouds in band 1 while in band 4 it has a better definition for low radiance objects such as shadows.
Click on PROCESSING → CLOUD DETECTION → CLOUD DETECTION in the main menu.
Input Layer:
Cloud Layer:
Click on the
button to select the layer to be used for cloud filtering and
corresponding band.
Shadow Layer:
Click on the
button to select the layer to be used for shadow filtering and
corresponding band.
Histogram:
Preview: check this box and on the New ROI button to draw a area to be used to preview the detection result.
Enter the minimum and maximum pixel value to isolate cloud and shadow objects.
Histogram analysis is generated in a chart to help define the interval.
Note: A Histogram is a bar graph that show how frequently data occur within certain ranges of the interval. The height of each bar gives the frequency in the respective interval.
Morphologic Operator:
These filters explore signal geometric properties (image geo levels). To these filters masks are structure elements and present values 0 or 1 in the matrix (3x3 – center pixel and neighbors) that correspond to the considered pixel. Basic morphological filters are medium, erosion and dilation.
Note: if morphologic filters are not applied, there will not be the removal of small rivers and noises.
Filter order: To change filter order click on up or down arrows.
Closing: click on this box and enter the value. Image closing generally chains erosion and dilation filters with the same structure element to obtain closing effects. Obtained by dilation filter chain, followed by erosion filter. Used to gulf removal and bay closing.
Opening: click on this box and enter the value. Image opening generally chains erosion and dilation filters with the same structure element to obtain opening effects. Obtained by the erosion filter chain, followed by the dilation filter. Used for isthmus break and cape and islands removal.
Output:
Repository -
Select one type of repository by
clicking on the
button to save the output layer as a file or on the
button to save it in the database.
Layer Name - inform the raster name.
Press the OK button to save the resulting contrasted raster.