The Explorer mode of the HEritage Data VIsualisation tool (HEDAVI) allows users to process on-the-fly, visualise, share and export Earth observation data from ESA’s Heritage and Third Party Missions.

Access to data anywhere on the globe are available from a large array of datasets (optical or radar, medium or high resolution, wide or medium swath), starting from the oldest one acquired back in 1984, to newly acquired data from active satellite missions.  

This tutorial focuses on how to find data in HEDAVI, using the “Finder” tool to build up a customised “Layerstack”. The use of the layerstack will be the subject of a future tutorial. 

1 Opening the Finder tool

The “Finder tool” is used to select the data to be visualised and processed on the “Display Area” of HEDAVI Explorer.

To access the “Finder tool”, open the “Service Panel” by clicking the “Services” tab, located in the menu. 

The “Service Panel” opens by default on the “Base maps” tab. Switch to the “Finder” tab. 

2 Using the Finder tool

2.1 Search criteria

In order to retrieve data, you have to define one or more criteria using the “Selection subpanel” of the Finder tab. Other subpanels become available after you submit the search request, once there are products listed in the “Results subpanel”. 

Search criteria are optional, but can be used to narrow down the search results. To activate a particular criterion, the box at the beginning of the corresponding line must be ticked (). When you have selected all of the search parameters of interest to you, use the “Search” button.

2.1.1  Geographic criteria

An area of interest (AOI) is used to focus research on a particular part of the globe. If no AOI is specified, the Finder will search for Earth Observation data on the entire planet. An AOI can be defined in different ways:

•  by using the tool on the “Display area” (first button on the left). Icons will appear in the “Geometry builder” at the top right of the image area to define a bounding box (default selection), a circle, a polygon or a corridor,

•  by importing a closed single polygon without holes contained in a KML, KMZ or SHP file input (second button on the left),

•  by using the footprint of one of the layers present in the layer stack (second button on the right), the camera is centred on the currently selected item,

•   by using the extent of the “Display Area” (right button) to define a “Bounding box”, the “Service Panel” is hidden and the camera then zooms out in order to better show the defined AOI.

Three other buttons are available:

• Use this button to edit the last geometry created using the “Geometry builder”,

• This button is used to centre the view on the last geometry created,

• This button deletes the last geometry you have drawn.

2.1.2  Minimum overlay between the product and AOI

Using the AOI criteria, you can find products that have a geodetic intersection with the defined AOI. The criteria is satisfied if the % selected is exceeded by 

• either the fraction of the AOI included in the product footprint 
• or the fraction of the product footprint included in the AOI.

Using the overlay, you can reduce the number of results, which helps to find products with a particular footprint.

2.1.3 Temporal criteria

You can set a temporal range to your search by selecting a start and/or end date. Both can be entered manually in YYYY-MM-DD date format, or by using the calendar tool on the right. In the same way, the time of day can be defined using either the clock or HH:mm:SS format.

On the calendar tool, pulldown menus allow the selection of the date and time of day.

Navigate between months using the single arrow buttons (yellow) or between years using the double arrow buttons (orange). 

2.1.4 Product status

It is possible to filter products by readiness status. This is useful when you are looking for a product that was previously prepared. Select the status of products by ticking the “Status” checkbox (red) and selecting the desired state using the drop-down menu (green).

•  “Ready” means the product has already been downloaded and prepared, it can be visualised and analysed immediately

•  “In progress” means the selected product is currently under preparation, its percentage of completion is displayed

•  “In queue” means that the product has been sent to the preparation queue but is not yet being prepared

•  “Unprocessed” means that the product has not been requested and must be prepared before it can be displayed. This is the default status.

•  “Error” means the product is not available since something unexpected happened in a previous preparation, causing an error.

2.1.5 Dataset selection 

The 'Dataset' criterion is used to enter the type of data selected. A tree widget lists the measures, which are available for search, processing, display and hyperlook dissemination and allows the selection of one or several of them for the search. These datasets are accessed by expanding each level and ticking the checkbox for the products you want.

The information symbol details the catalogue of available datasets classified by provider and identifier with a description of the dataset.

The first-level items in the drop-down menu identify the data provider, the second level specifies the satellite that acquired the images, the third indicates the dataset and the fourth indicates the instrument and/or mode. 

2.1.6 Cloud cover notation

The "Cloud Cover Notation" (CCN) criterion is used to define the maximum percentage of cloud cover in available optical data. The tool retrieves results based on the amount of cloud cover defined in the dataset’s metadata.

If the maximum cloud cover is set at 25%, for example, only the first three products will be selected by the Finder service in the example below.

2.1.7 Limiting number of returned results

You can limit the maximum number of results returned by a search. The number of results ranges from a maximum of 500 or a minimum of none ("-", which only counts matching products). The default value is 100.

After the number of results is found, you may proceed to see the list of products, or cancel if you wish to refine the search.

The higher the maximum number of returned results, the longer the search is likely to take. To reduce response time, it is advised to fragment the time intervals (for example, search by year or month), or to select a smaller number of datasets in each search.

2.2 Search results

2.2.1 Number of results found

When you begin a search, an intermediate window shows the number of products found per dataset, up to the maximum specified.

If no products have been found or if the number of products is too large, the search can be cancelled and the criteria adjusted. Otherwise, click on "Continue" to display the list of products found.

2.2.2 List of results found

Products matching all criteria are listed, up to the maximum specified. For each product, some metadata are listed as well: dataset, acquisition date and possibly, granule name, cloud cover notation, orbit direction or polarisation, which do not show by default. Results can be sorted according to each of these fields.

3 Conclusion

Only prepared products are immediately available for visualisation by selecting this in the list of results. In other cases, only the footprint of the product shows until the product is prepared. The use of this list of results will be explained in a dedicated tutorial highlighting how to visualise products that are not yet “Ready”, and how to make the most of the features of the layerstack.