Dr Melanie Collins
Scientist in the Upper Air Development, Observations R&D, Met Office

Presented by Met Office and University of Reading

Dr Will Winter
Scientist in Radar Systems Development, Observations R&D, Met Office

Further reading

Weather forecasts bring the output of advanced remote sensing to a wide audience.

Storms -2-320Weather radar. Credit: Adam Curtis

Remote sensing techniques used by the Met Office help to warn of heavy rainfall and flooding, as well as a new hazard - volcanic ash. For the latter, the detection of volcanic lightning has been shown as a potentially useful early warning sign of eruptions in remote parts of the world.

How it works

The Met Office operates a lightning detection network called ATDnet, which detects lightning from very long ranges (up to 10,000km) due to the very low frequency (10kHz) emissions of lightning strokes. A lightning stroke is located using small differences in the time of arrival of a signal at detectors spaced widely around the globe. Recent improvements in the sensitivity of the system have enabled volcanic lightning to be monitored.

The scientists behind this exhibit also operate a network of 15 weather radars across the UK. These scan the horizon by sending short pulses of microwaves (5.6GHz frequency) and listen to the echoes from raindrops. The time difference between sending the signal and receiving its echo is used to locate the rainfall. The strength of the return echo indicates the rainfall intensity and by measuring the Doppler effect of return echoes, the radar can measure wind speed.

Very recently, the radars were adapted to measure humidity by looking at very small changes in the apparent range of fixed targets, such as hills or houses. These changes are caused by variations in the refractive index of the air between the radar and the target. The radar receivers are now also sensitive enough to detect the faint microwave emissions from storms several hundred kilometres away.

Lead image: Volcanic lightning. Credit: Lucas Jackson