This animation shows two images of the same area acquired by two different instruments on the Envisat satellite: MERIS and the Advanced Along-Track Scanning Radiometer.
The first image shows northern France with Paris in the centre. The river flowing through the city and into the English Channel is the Seine. East of Paris, vineyards and fields of the famous Champagne-Ardenne region appear lighter in colour.
The second radiometer image in the animation shows heat, with yellows and reds depicting higher temperatures compared to the cooler blue areas. In this image, urban areas south of Paris – such as Orléans – stand out.
The temperature in densely urbanised areas can be several degrees higher than in nearby rural areas, a phenomenon known as the ‘urban heat island’ effect.
These heat islands are particularly noticeable at night. During the day, cities accumulate solar radiation, keeping them warmer in comparison to the surrounding land, which cools off quicker after the Sun sets.
The negative effects of this increase in urban temperatures are multiple: health problems, higher energy demand, air pollution and water shortages.
Monitoring thermal radiation can help city planners to design more 'liveable' cities, assist civil protection authorities in taking adequate measures during heat waves and create maps of energy efficiency.
The background image was acquired on 20 February 2012 by Envisat’s MERIS, while the colours representing temperature come from data acquired by Envisat’s Advanced Along-Track Scanning Radiometer on 23 May 2011. The radiometer measured thermal-infrared radiation to take the temperature of Earth’s land and sea surfaces.
After ten years in orbit, contact with Envisat was suddenly lost on 8 April and the mission has come to an end.
Envisat’s archived data will continue to be exploited for studying Earth’s land, atmosphere, oceans and ice caps for years to come.
The Image of the Week is featured on ESA Web-TV, broadcast online every Friday at 10:00 CEST.