DISMapper tutorial
The service targets the automated detection of significant changes in a landscape that can be triggered by natural disasters (e.g. landslides, burnt areas). It is based on the analysis of a multi temporal stack of optical images acquired before and after the event. It supports calibrated datasets from the Sentinel-2 mission. Output of the service is a set of intensity and binary mask from detected changes.
DISMapper service description and specifications are available in this section.
Select the processing service
After the opening of the activation workspace, in the right panel of the interface, open the Processing Services tab. Select the processing service DISMapper.
The "DISMapper"[^1] panel is displayed with parameters values to be filled-in.
Check input datasets using multiple filter criteria
Input of this service are:
-
Sentinel-2 L2A Calibrated Datasets
-
and two Auxiliary Datasets (Copernicus GLO30 DEM, ESA WorldCover).
In DISMapper the user does not need to specify the input datasets because the service automatically retrieves all necessary Calibrated and Auxiliary Datasets from the Charter Mapper catalog.
However before employing DISMapper it is better to check which available datasets are present in the activation workspace over the desired area of interest.
Select the area in which you want to make your analysis, e.g near La Perla, Province of Huaral, Lima, Perú.
From the Navigation and Search toolbar (located in the upper left side of the map), click on Spatial Filter and draw a square AOI La perla municipality. This spatial filter allows you to select only the EO data acquired over this area.
Now it is possible to identify how many Sentinel-2 L2A Calibrated Datasets are available over the area. From the top of the left panel, use Filter Criterias to search for "sentinel-2" data collections from the list.
In addition to Sentinel-2 L2A Calibrated Datasets, DISMapper requires in input also the Copernicus DEM and the ESA World Cover auxiliary datasets. These are derived in systematic by the Charter Mapper and offered within a Auxiliary Dataset under the Dataset data context. To quickly retrieve these Auxiliary Datasets over your AOI, you can keep the same spatial filter employed in the search of the input Sentinel-2 L2A Calibrated Datasets, and from the Filter Criteria box add the auxiliary data
value in the Satellite filter.
Fill the paramters
After this check on the required input, you can employ DISMApper, by filling in the parameters as described in the following sections.
Job name
Insert as job name:
DISMapper - Landslide La Perla Alta Peru 20230415
Event date
In the first parameter you shall specify the event date in the format YYYYMMDD. The even occurred on the 15th April of 2023. Insert the value 20230415 in this field.
First post event date
In this second parameter (optional) you can specify the first post event date to be used in the search for post-event images after this date (e.g. when the event is ended). The First post event date
and event date
are both employed in the search of input satellite imagery. When necessary, the First post event date shall be inserted in the format YYYYMMDD
. If empty, the service searches for post-event images acquired just after the start date of the event (e.g. assuming that the event will end in 1 day). For this use case you can leave this field empty.
Hazard event type
In the third parameter you need to select the hazard type among these options: wildfire
, landslide
, flood
or volcano
. The event over La Perla Alta is a landslide thus you must select the landslide option from the list.
Area of interest expressed as Well-known text
In the fourth parameter you must define the “Area of interest as Well Known Text”. The AOI can be defined by using the drawn polygon defined with the area filter.
Tip
In the definition of “Area of interest as Well Known Text” it is possible to apply as AOI the drawn polygon defined with the area filter. To do so, click on the button in the left side of the "Area of interest expressed as Well-known text" box and select the option AOI from the list. The platform will automatically fill the parameter value with the rectangular bounding box taken from the current search area in WKT format.
Max Cloud coverage allowed for the pre event products selection
In the sixth parameter you must specify the cloud coverage threshold to be used when selecting valid pre-event Sentinel-2 L2A Calibrated Datasets. As an example if you want to consider only cloud free images and partially covered images up to 25% of cloud coverage you must insert the value 25
. For this use case you can leave the default values as 25%.
Max Cloud coverage allowed for the post event products selection
In this last parameter you must specify the cloud coverage threshold to be used when selecting valid post-event Sentinel-2 L2A Calibrated Datasets. For this use case you can leave the default values as 75%.
Run the job
Click on the button Run Job and see the Running Job
You can monitor job progress through the progress bar.
Results: download and visualization
Once the job is completed, click on the button Show results at the bottom of the processing service panel.
Tip
You can also save the parameters employed in this job by clicking on the Export params button in the right panel. This allows you to copy all your entries to the clipboard. This is meant to be used for a quick re-submission of a similar job after a fine tuning of the parameters (e.g. to add a color formula later).
Visualization
See the result on the map. The preview appears within the area defined in the spatial filter. The Normalized Relative Difference Index (NRDI) is displayed with a "BlueYellowRed” color palette. Areas with no changes are in blue tones; areas with significant changes are in red tones.
To get more information about the product just click on the preview in the map, and from the bubble showing the name of the layer then click on the Show details button.
Tip
To quickly access Product Details double click on the layer from the Results list.
In the left panel of the interface, the details of Job Result will appear with Product metadata. Furthermore by clicking on Layer styling you can also access to the View options. In here it is possible to select the asset, see histogram/s of the Product which is visible in the map, set color formula, change Filters (e.g. Brightness, Opacity).
DISMapper generates two Normalized Relative Difference Index (NRDI) products: NRDI_c with continuous data values in the range [0,1]; and NRDI_t with binary data values [change / no change] based on thresholds as explained in the service specifications.
You can for instance switch to another asset to visualize the pre-event multitemporal mosaic as True Color Composite
or the overview from the post-event multitemporal mosaic.
Download
In the DISMapper service the following files are produced:
- dismapper_NDRI_c: Normalized Relative Difference Index (NRDI) with continuous data values in the range [0,1] as single band raster in COG format,
- dismapper_NDRI_t: binarization map obtained from the NRDI [change / no change] as single band raster in COG format,
- overview_dismapper_NDRI_c: RGBA product from the
dismapper_NDRI_c
asset using the "BlueYellowRed” color palette including transparency as multi band raster in COG format,, - overview_dismapper_NDRI_t: RGBA product from the
dismapper_NDRI_t
asset including transparency as multi band raster in COG format,, - overview_dismapper_rgb_mosaic_before: RGBA product from the pre-event multitemporal mosaic as True Color Composite in COG format,
- overview_dismapper_rgb_mosaic_after: RGBA product from the post-event multitemporal mosaic as True Color Composite in COG format.
These products can be downloaded by clicking on the Download button located at the bottom of the Product Details tab in the left panel.