Machu Picchu: A tool for improved imaging in difficult areas
The strong capability of satellite radar data has already been demonstrated, especially in cloudy areas or for detecting small movement using the interferometry technique. However the selection of radar satellite data is complex and without great care the satellite can simply miss part of a mountain. Defining adequate acquisition parameters is complex in relief areas where the geometrical effects of layover, foreshortening or shadow must be taken into consideration.
To facilitate the use of radar data and support UNESCO’s heritage initiative, the French Space Agency (Centre national d’études spatiales - CNES) decided to provide a tool for SAR visibility prediction. The tool is designed to help users to select the most appropriate SAR data acquisition parameters for the imaging of a particular Area Of Interest (AOI).
CNES appointed Altamira Information to develop the tool. It integrates the main civilian SAR missions (ERS, Envisat/ASAR, Radarsat-1 &-2, ALOS/PalSAR and TerraSAR-X) and selects the most suitable parameters for each in terms of acquisition modes and incidence angles according to the characteristics of the AOI. Once the appropriate parameters and a Digital Elevation Model have been chosen, a SAR image is generated, allowing the user to check the visibility of its AOI and thus confirming the selection of the most effective mission and acquisition parameters.
Following some preliminary work conducted at CNES with Envisat/SAR data, the Machu Picchu sanctuary (Peru), a UNESCO World Heritage site, was selected as AOI for the pilot phase to validate the tool. Due to its location in a highly mountainous area, the site combines all kinds of potential geometric distortions inherent to SAR imaging. Layover, foreshortening and shadows will be taken in consideration in order to select the optimum parameters for SAR observation of zone.
This tool is a CNES contribution to the Open Initiative and the SAR users community; it was made available free of charge.
With this effective tool, CNES has made a significant contribution that is of great use to the entire radar remote sensing community. Developed for UNESCO and available to all, this tool allows each radar user to identify blind spots ahead of time, areas where the radar-satellite is ‘blind’ and cannot capture accurate information due to the terrain topography.
The ‘Machu Picchu problem’ posed by UNESCO was in reality a huge challenge to meet for radar satellite technology!