By Guest Work 28/12/2016

When Tony Bromley heads to the hills in January he’s taking along a bag of party balloons and some cardboard coffee cups to help him with some complex measurements involving power lines along the National Grid.

The NIWA atmospheric technician is aiming “to define the sag”.

“Power lines expand with heat and the more power that goes down the line the hotter they get. When that happens the lines sag in the middle of the span between power pylons. It’s essential to know how low the sag could go to ensure the lines aren’t going to touch anything.”

NIWA’s Tony Bromley and Sally Gray (right) and prepare to release a weather balloon. Credit: Dave Allen. Source: NIWA.

Measuring the potential depth of a sag involves complex calculations involving temperature, wind speed and direction, pressure, humidity and solar radiation measurements many metres off the ground. For instance, the wind has a cooling effect but the amount of cooling depends if it is travelling across or along the lines.

All these measurements are used as part of the equation to work out the minimum distance between the lines and other objects, such as trees. Too close means the risk of outages and other issues. A helicopter will operate at the same time taking precise distance measurements via laser.

Mr Bromley and his team will cover 1600km of lines over four weeks from Southland to the Bay of Plenty and Auckland. They will set up temporary meteorological stations at ground level along the length of the lines and then fill party balloons with helium.

The balloons will be attached to the biodegradable coffee cups which contain transmitting sensors sending weather information back to the ground. Once a pre-set height has been reached, some clever programming triggers an electric current that burns through the string, releasing the balloon. The coffee cup falls to the ground, is retrieved and used again.

“The transmitters will only need to ascend to a height of around 100m at most, so we can see where they land. They also transmit a signal giving their actual location on the ground and a small handheld GPS unit can be used to direct us to that location – very useful if the transmitter is hidden in long grass. It is a very efficient use of our technology especially being able to re-use the instruments many times.”

Summer is for scientific fieldwork. This article is from the NIWA Summer Series, sharing the stories of scientists heading into the wild blue yonder.

Featured image credit: NIWA

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