Over The Horizon

Scintillating Studies

Arguments over water use in rice paddies in Japan are to gain some relief from the use of equipment designed and built by HortResearch scientists. There is fierce competition for water in Japan between industry, agriculture and the 124 million-strong population, and despite high rainfall, water supplies often run low.

Alan Green of HortResearch's Environmental Physics group went to Tsukuba as part of a collaborative programme with the Japanese Agro-environmental Research Institute. The work used the institute's large aperture scintillometer to measure the water usage of the rice paddies.

The scintillometer measures heat flux in the atmosphere by measuring the fluctuations an infrared beam encounters as it passes over a surface. As the beam travels through the air it is distorted; the amount of distortion is related to the density of the air, temperature variations, evaporation of water and so forth. This distortion is measured by a receiver and, using standard energy balance equations, water usage and other aspects can be calculated.

Green compares the instrument to a form of telescope and the phenomenon it is measuring as akin to a mirage.

The beam was trained two metres above the rice "canopy", over a distance of 200 metres or so. The HortResearch scientists hadn't tried the equipment over such wet surfaces before, and Green has been keen to see the new application in practice.

"We tend to work over dry surfaces," notes Green. New Zealand pastures differ considerably from Japanese rice paddies, introducing a series of interesting scientific problems according to Green, but the basic principles remain the same.

A further advantage of the scintillometer is that it works on large spatial scales -- over hundreds of metres and up to 3-5 kilometres. This enables it to provide an average of conditions over that scale, which can be more useful than single point measurements that can be affected by localised conditions. The scale also means that results can be compared against satellite images for cross-verification.

Japanese scientists are enthusiastic about the new instrument and are hoping to continue to work with HortResearch. Green says that the work offers a chance for exchanges with younger researchers as well as opportunities in other parts of Asia.

The work in Japan offered complications not found in New Zealand. As well as working at the hottest, most humid period of the year, Green also encountered the typhoon season which saw large quantities of water dumped on the paddies in a short amount of time. This, combined with farmers eager to harvest their crops, meant that it wasn't the best time to begin such work, but Green sees it showing a great deal of promise for the future.