El Salvador has voted to recognise bitcoin as legal tender, and there is a great deal of interest globally in digital currencies that provide an alternative to cash. However mining bitcoin, the intensive computation needed to claim ownership of new Bitcoins, uses vast amounts of electricity – more than many countries produce. Currently most of this energy is supplied from traditional fossil fuel sources rather than renewables. Larisa Yarovaya from Southampton Business school discusses whether Bitcoin is really worth the environmental cost. Drones for surveying disaster areas with cameras have been around for a while , but now researchers at the Fraunhofer Institute for Communication, Information Processing, and Ergonomics have revealed a drone based system that can listen to the environment and pinpoint people who may be in distress following floods or earthquakes. Researcher Macarena Varela describes the drone and its microphone array.And lidar, the survey method which used lasers to reveal topographic detail is now finding a use in mapping Rio De Janero’s Favelas. These areas of informal housing developed in largely unplanned ways, but a wider understanding of their geography might help those who live there access essential services. The lidar survey has the advantage of being conducted without revealing the inhabitants personal information say MIT researchers Arianna Salazar Miranda and Claire Gorman.(Image: Getty Images) The programme is presented by Gareth Mitchell with expert commentary from Angelica MariStudio Manager: Sue Maillot Producer: Julian Siddle