HASARD Dual Image tutorial

This service provides a binary flood mask by applying an automatic change detection algorithm between a pair of pre- and post-event Sentinel-1 datasets selected by the user (one before and one after the event). The service analyzes the reference and flooded images and retrieves the increased water extent with respect to the reference (areas considered as standing water bodies are removed).

HASARD Dual Image 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 HASARD Dual Image.

The "HASARD Dual Image"¹ panel is displayed with parameters values to be filled-in.

Find the data using multiple filter criteria

• Select the area in which you want to make your analysis, e.g over the central region of Thailand.

• From the Navigation and Search toolbar (located in the upper left side of the map), click on Spatial Filter and draw a square AOI over the Nakhon Sawan Province in Thailand. This spatial filter allows you to select only the EO data acquired over this area.

• From the top of the left panel, use Filter Criterias to search for “Radar” and "Sentinel-1" data collections from the list.

• After the query the list will be updates as the one shown in the next image.

• Now it is possible to choose a pair of "Flood" and "Reference" co-pol backscatter images from SAR Calibrated Datasets to be used for the flood detection analysis. This pair must come from the same sensor and shall have the same radar geometry (incident angle, orbit path).

• As an example you can choose the following pair:

  • Reference: SENTINEL-1A C-SAR IW VV/VH 172 2021/09/22 11:29:45

  • Flood image: SENTINEL-1A C-SAR IW VV/VH 172 2021/10/04 11:29:45

• Alternatively, you may also consider the S1 pair exploited in the VAPs² preapared by UNITAR/UNOSAT³ for Activation-734⁴.

Fill the paramters

After the definition of spatial and time filters, you can employ HASARD Dual Image, by using a suitable pair of Calibrated Datasets from Sentinel-1 data.

To do so you can fill the parameters as described in the following sections.

Job name

• Insert as job name:

HASARD Dual Image Sentinel-1 22/09 - 04/10 2021 Nakhon Sawan Thailand 

Reference input

Drag and Drop the selected items:

1. flood image (Sigma0 VV during crisis)

2. reference image (Sigma0 VV before the event)

in the Flood event image and the Reference image fields respectively.

HSBA parameters

The other four mandatory parameters, Splitting level, Check bimodal distribution (Ashman D), Minimum number of pixels per tile, Number of pixels for small object removal represents the parameters of the retrieval algorithm. Default values can be used for these four HSBA parameters.

Area of interest expressed as Well-known text

The “Area of interest as Well Known Text” can be defined by using the drawn polygon defined with the area filter.

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.

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

{
   "aoi": "POLYGON((99.487 15.552,99.487 16.515,100.605 16.515,100.605 15.552,99.487 15.552))",
   "pre_event": "https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid857}]/search?format=json&uid=call857_S1A_IW_GRDH_1SDV_20210922T112945_20210922T113010_039794_04B4ED_B07E-calibrated",
   "post_event": "https://catalog.charter.uat.esaportal.eu//charter/cat/[chartercalibrateddataset,{callid857}]/search?format=json&uid=call857_S1A_IW_GRDH_1SDV_20211004T112945_20211004T113010_039969_04BB05_888C-calibrated",
   "hsba_depth": "3",
   "ashman_coeff": "2.4",
   "min_pixnb_bimodd": "1000",
   "blobs_size": "20"
}

Visualization

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 “HASARD flood bitmask derived from S1A_IW_GRDH_1SDV_20210922T112945_20210922T113010_039794_04B4ED_B07E-calibrated and S1A_IW_GRDH_1SDV_20211004T112945_20211004T113010_039969_04BB05_888C-calibrated” will appear and then click on the Show details button.

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 see histogram/s of the Product which is visible in the map, set color formula, change Filters (e.g. Brightness, Opacity).

Download

In the HASARD Dual Image service the following files are produced:

• flood-mask: single-band geophysical asset as Flood bitmask (1=Flooded, 0=Not-flooded) as single band GeoTIFF in COG format,
• overview-flood-mask: multi-band asset as RGBA from Flood bitmask in the blue channel including transparency as multi band GeoTIFF in COG format,
• pre-s0_db_c_vv: single-band geophysical asset s0_db_c_vv product from reference image as single band GeoTIFF in COG format,
• post-s0_db_c_vv: single-band geophysical asset s0_db_c_vv product from flood image as single band GeoTIFF in COG format,
• overview-vv-pre: multi-band asset as RGBA in grayscale from reference image as multi band GeoTIFF in COG format,
• overview-vv-post: multi-band asset as RGBA in grayscale from flood image as multi band GeoTIFF 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.