# COMBI-Plus tutorial

This service provides an advanced environment to create RGB composites at full resolution from a fully customizable combination of multiple assets from single or multiple EO data products (optical or radar). The output has the finest resolution as of the input data (only if all selected bands are coming from the same sensor).

## Select the processing

• After the opening of the activation workspace (e.g. [Act-100/Call-100] Global Activation for Validation, on the training instance of the processing Environment), in the right panel of the interface, open the "Processing Service" tab and select the processing service “Multi-Sensor Band Composite”.

The "Advanced Multi-Sensor Band Composite (COMBI-Plus)" panel is displayed in the right panel of the interface with a series of parameters values to be filled-in.

### Reference input

• Click on the Dataset button in the left side of the menu bar and select the “Optical” data collection from the list.

• Select the area for which you want to do an analysis, e.g over the Etna Volcano in Southern Italy.

• From the Navigation and Search toolbar (located in the upper left side of the map), click on “Spatial Filter” and draw a square around the mount Etna. This spatial filter allows you to select only the EO data acquired over this area.

• From the left panel, click on the lens icon and in the Search Panel set date value 2021-02-10 in time:start and 2021-02-22 in time:end fields. Click on Search to.

### Fill the parameters

• After the definition of spatial and time filters, you can apply the multi sensor band composite, by combining, for example, two swir22 assets from a pair of images to generate a multitemporal RGB composite (red for pre- and cyan post-event). The first one can be the Landsat-8 OLI L1TP image acquired on 18/02/2021 during the lava flow after the volcano eruption. The second one can be the Sentinel-2B MSI L1C image acquired on 21/02/2021 during the following evolution of the lava flow. Thus, in the RED channel the first swir22 asset can be derived from the calibrated Sentinel-2B dataset (S2B MSI L1C 20210221. The second asset swir22 from Landsat 8 calibrated data (LC08 L1TP 20210218) can be employed instead in the GREEN and BLUE channels.

• Now you can fill the parameters as following:

• Insert as job name “Multi-Sensor Band Composite (MT S2&L8 2021 Etna, Italy)”.
• Drag and Drop the pair of selected items in the “Input Product References” field in the following order (first image is the one having the most recent sensing time of the pair):
1. S2B_MSIL1C_20210221T095029_N0209_R079_T33SVB_20210221T105506
2. LC08_L1TP_188034_20210218_20210304_01_T1
• To define an “Area of interest as Well Known Text”, apply as AOI the drawn polygon defined with the area filter. Click on the button in the left side of the AOI ad WKT parameter box and select the option AOI from the list to automatically define the WKT values.
• The remaining mandatory parameters to be filled in are three s-expressions, one for each of the RGB channels. If needed it is also possible to define an s-expression for the alpha channel to set transparency.
• Insert as red_expression: “(interp 1.swir22 (asarray 0 10000) (asarray 0 1))”
• Insert as green_expression: “(interp 2.swir22 (asarray 0 10000) (asarray 0 1))”
• Insert as blue_expression: “(interp 2.swir22 (asarray 0 10000) (asarray 0 1))”

## Run the job

• Click on the button Run Job and see the Running Job

• After few minutes, see the Successful Job:

• Click on the button Show results

• See the result on the map. The preview appears within the area defined in the spatial filter.

• To get more information about the product just click on the preview in the map, a bubble showing the name of the layer “multi-sensor-composite” will appear and then click on the “Show details” button. In the left panel of the interface, all the details of the layer of the product will appear.

• In the Multi-sensor Band Composite service the following files are produced:

• “1.swir22”: asset swir22 product from reference image 1, as single band TOA reflectance GeoTIFF in COG format (physical meaning product from optical calibration),
• “2.swir22”: asset swir22 product from reference image 2, as single band TOA reflectance GeoTIFF in COG format (physical meaning product from optical calibration),
• “multi-sensor-composite”: output multi-sensor-composite product given as 4 bands RGBA 8-bit GeoTIFF in COG format
• “red-channel”: R-channel product from Multi-sensor-composite RGBA given as single band 8-bit GeoTIFF in COG format,
• “green-channel”: G-channel product from Multi-sensor-composite RGBA given as single band 8-bit GeoTIFF in COG format,
• “blue-channel”: B-channel product from Multi-sensor-composite RGBA given as single band 8-bit GeoTIFF in COG format.
• To download one of the products listed above, just click on the “Download” button under the Details tab in the left panel.

Tip

You can also save the parameters employed in this job by clicking on the “Export params” button in the left 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. in case you need to just to refine a single s-expression).

Below is reported the syntax which includes all the parameters employed in this example.

   {
"input_reference": ["https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_S2B_MSIL1C_20210221T095029_N0209_R079_T33SVB_20210221T105506-calibrated",
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_LC08_L1TP_188034_20210218_20210304_01_T1-calibrated"],
"aoi": "POLYGON((14.834 37.635,14.834 37.862,15.113 37.862,15.113 37.635,14.834 37.635))",
"red_expression": "(interp 1.swir22 (asarray 0 10000) (asarray 0 1))",
"green_expression": "(interp 2.swir22 (asarray 0 10000) (asarray 0 1))",
"blue_expression": "(interp 2.swir22 (asarray 0 10000) (asarray 0 1))"
}


## Sample results

The Multi-Sensor Band Composite service can be employed also to generate RGB from advanced band combination as well as to more inputs. Below are listed show cases of possible results obtained from this service.

Multi-temporal and multi-mission RGB composite - Volcano Eruption of Etna in Italy.

This example shows a multitemporal RGB composite obtained from three acquisitions from multi-sensor multispectral images acquired over the Etna volcano in February 2021.

Input calibrated reference datasets are the following:

1. Sentinel-2B MSI multispectral image acquired on 21/02/2018 (lava-flow).
2. Landsat-8 OLI multispectral image acquired on 18/02/2018 (lava flow).
3. Sentinel-2A MSI multispectral image acquired on 16/02/2018 (eruption).

Below are reported all the parameters employed in this job.

{
"input_reference": [
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_S2B_MSIL1C_20210221T095029_N0209_R079_T33SVB_20210221T105506-calibrated",
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_LC08_L1TP_188034_20210218_20210304_01_T1-calibrated",
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_S2A_MSIL1C_20210216T095101_N0209_R079_T33SVB_20210216T110754-calibrated"
],
"aoi": "POLYGON((14.845 37.638,14.845 37.873,15.123 37.873,15.123 37.638,14.845 37.638))",
"red_expression": "(interp (norm_diff 1.swir22 1.swir16) (asarray -1 1) (asarray 0 1))",
"green_expression": "(interp (norm_diff 2.swir22 2.swir16) (asarray -1 1) (asarray 0 1))",
"blue_expression": "(interp (norm_diff 3.swir22 3.swir16) (asarray -1 1) (asarray 0 1))"
}


In addition to the RGB preview, it is also possible to visualize separately each RGB channel and to apply a proper layer style. Just click on the image in the map, a bubble showing the name of the layer “multi-sensor-composite” will appear and then click on the “Show details” button. In the left panel of the interface, all the details of the layer of the product will appear. Click on Layer Styling. Click on the Single asset section, select the asset “blue-channel”, then select Magma as color map, and click on the “Apply” button. The new asset will appear on the map. The swir22 asset employed in the creation of the Blue channel is derived from the third input reference (S2A_MSIL1C 20210216) and shows the early stage of Etna eruption acquired from S2A MSI L1C on 16/02/2021. For a better visualization of the lava flow, set 0.5 as minimum and 1 as maximum, and opacity at 50%, then click the below “Apply” button.

Same procedure can be applied for the remaining two channels (green and blue) derived, respectively, the swir22 asset of first and second input references.

Lava flow activity of Etna acquired from Landsat-8 L1TP on 18/02/2021.

Lava flow activity of Etna acquired from Sentinel-2B on 21/02/2021

Multitemporal RGB composite - Flood event in Palu 2018

Multitemporal Red-cyan RGBA composite over Palu from a pair of UK-DMC-2 SLIM-6 L1T calibrated datasets.

Input calibrated reference datasets are the following:

1. UK-DMC-2 SLIM-6 multispectral image acquired on 19/07/2018 (post-event).
2. UK-DMC-2 SLIM-6 multispectral image acquired on 14/10/2018 (pre-event).

Below are reported all the parameters employed in this job.

{
"input_reference": [
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_U2009043_000000_015499_s_L1T-calibrated",
"https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100}]/search?format=json&uid=call100_U20093d4_000000_015499_s_L1T-calibrated"
],
"aoi": "POLYGON((119.834 -1.013,119.834 -0.874,119.94 -0.874,119.94 -1.013,119.834 -1.013))",
"red_expression": "(interp 1.nir (asarray 0 10000) (asarray 0 1))",
"green_expression": "(interp 2.nir (asarray 0 10000) (asarray 0 1))",
"blue_expression": "(interp 2.nir (asarray 0 10000) (asarray 0 1))"
}


Intra Sensor RGB composite - Water mask in Greece 2018

RGBA composite over Palu from a single Pleiades ORT calibrated dataset.

Input calibrated reference dataset is:

1. Pleiades ORTHO multispectral image acquired on 30/07/2018.

Below are reported all the parameters employed in this job.

{
"input_reference": "https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid100},mission_spot_6]/search?format=json&uid=call100_ORT_SPOT6_20180730_083843100_000-calibrated",
"red_expression": "(interp 1.red (asarray 0 10000) (asarray 0 0))",
"green_expression": "(interp 1.red (asarray 0 10000) (asarray 0 0))",
"blue_expression": "(where (>=  (norm_diff 1.green 1.nir) 0.3) 1 0)",
"alpha_expression": "(where (>=  (norm_diff 1.green 1.nir) 0.3) 1 0)"
}