The Heritage Data Visualisation tool (HEDAVI) is a platform developed by the French Science Consulting for Earth Observation group, VisioTerra, which allows users to freely access over 40 years of ESA Earth Observation Heritage data, Third Party Missions and some Copernicus data. It offers two main types of user functions: the HEDAVI Explorer, which enables users to access the products of their choice and display them with their own rendering (which will be described in a future article), and the HEDAVI Discover, which allows users to access existing material in a simple way.

Learn more about the HEDAVI Discover function in this step-by-step guide to its two modes.

HEDAVI Discover encompasses two main features, one of which is to show multidate Envisat ASAR global synthesis, while the other is to display case studies (so-called stories) on a virtual globe.
 

Stories

To open an existing case study, use the “Stories” button (highlighted in orange in this image) located at the top right of the screen. The Stories are selected by default, and displayed as icons on the globe. Each icon represents a different case study with its location and theme.

1 Gallery panel

The Gallery panel shows all existing stories as a series of thumbnails on a ribbon that opens at the bottom of the screen.

1.1 Opening the Gallery

Open a story (case study) either by directly clicking on one of these icons, or by clicking on a thumbnail using the “Gallery Panel”. Open the Gallery Panel by using the button on the bottom left of the screen. In either case, the associated case-study will be displayed.

1.2 Filtering the Gallery

The “Gallery panel” can be filtered to show stories related to a particular theme. The example below shows the stories filtered by “Natural hazards”.

2 Selection of a case study

Once a story (case study) has been opened, the “Story panel” is shown. In this example, the case study is about the Piton de la Fournaise volcano, on Réunion Island. When opening the story, your view is centred on the location of the case study.

3 Visualisation of a case study

3.1 Opening a story

The case-study is accessed with the “View story” button in the “Story panel”. It opens the first view of a satellite image in the story by default, and focuses the view over that location.

3.2 Navigation within a case study

View other images in the story using the “Previous” and “Next” buttons. Your position on the globe will change to the location of the image, and it will display a description.

Synthesis

The second main feature of HEDAVI Discover is to show multidate Envisat ASAR global composites called “synthesis”.
 

1 Visualisation of a synthesis

In order to display a synthesis, open the “Synthesis” button located at the top right of the screen. This opens the Synthesis panel on the bottom left.

No synthesis is displayed by default, so select one of the calibrations listed in the panel. By default, the synthesis view shows a full cycle (35 days) of Envisat ASAR WSM acquisitions. It combines co-polarised acquisitions in VV and HH polarisation, both in ascending and descending views.

You can also visualise the globe in 2D to view the full cover of the synthesis over a map.

2 Changing the processing parameters of a synthesis

2.1 Selecting radar calibration

Selecting a processing type from the list immediately changes the visualisation of all images. There are five radar processing calibrations available:

• Digital Numbers (DN) reprojected on the ellipsoid
• γ0 orthorectified using Copernicus DEM
• γ0 orthorectified using Copernicus DEM, with a Copernicus Land/Sea mask applied to show only land areas
• σ0 orthorectified using Copernicus DEM
• β0 orthorectified using Copernicus DEM

2.2 Adjusting the brightness and contrast

The brightness and the contrast of the radar synthesis can be adjusted using the ‘-‘ and ‘+’ buttons. These modifications can be reset to the default values if needed.

3 Selecting the date of the synthesis

The time range of the synthesis can be changed. Available images extend from May 2002 to April 2012. Change the time range in one of the following ways:

• Drag the time range left or right
• Use the directional arrows on your keyboard
• Drag the start or end date in the range to an earlier or later date
• Use the arrows at the bottom left and bottom right

All of the images used in this guide are copyright ESA/processed by VisioTerra.

According to Guillaume Aurel, engineer of VisioTerra, “HEDAVI Discover provides an easy way to view images from Earth observation Heritage Missions. It is an interactive tool in which users can zoom in, zoom out, pan and rotate the camera as they wish. The ‘Synthesis mode’ allows anyone to display almost any radar images acquired during the 10 years of the Envisat mission in a single click. The ‘Story mode’ highlights both short-lasting events of the past and long process phenomena owing to HEDAVI the capability to display images spanning four decades.”

Visit HEDAVI Discover to learn more and use these features.