At the heart of the remote sensing industry

Remote Sensing Technology Center of Japan




How much rice is planted, and what is the extent of rice paddy flooding? See the state of farming with a radar.

Observing rice with penetrating cloud

A defining feature of rice paddy agriculture is the flooding of fields before planting. The Phased Array type L-band Synthetic Aperture Radar (PALSAR, active microwave sensor) mounted on ALOS is able to distinguish rice paddies from other farm land.

When observed by PALSAR, bodies of water are rendered as dark patches. As the rice shoots begin to hide the surface of the water, the image starts to look brighter (see image above). In other words, an area will appear dark at the time of rice planting, and the lightening of its color over time identifies it as a rice paddy. A feature of microwaves is they can produce images regardless of weather, and the long L-band wavelength of the PALSAR is especially useful because its performance is not affected by large cloud formations such as cumulonimbus. This is a unique strength of the PALSAR sensors mounted on the ALOS.

Individual rice paddies and fields are classified in data as polygons and therefore can be distinguished with considerable accuracy by searching for polygonal shapes alone. As the surface area of each polygon is also measured, the area of rice growing acreage can be calculated.

Total area of planted rice in Thailand


In Thailand, PALSAR data by ScanSAR is used to study the validity of crop statistics such as the total area of the rice planted in the country. Due to the rapid growth of crops during the Asian rainy season, it is crucial that technology not be affected by clouds.

Testing is also continuing on the use of PALSAR imagery in studies on the status of crops such as corn and sugar cane. It is possible to distinguish large crops such as corn and sugar cane using microwaves by observing growth in the volume of biomass (i.e. their physical growth).

Surveillance and planning uses

Many projects are expecting to utilize a unique advantage of microwave sensors which can observe the ground regardless of the weather.

For example, a project in Southeast Asia considers designing the micro insurance for farmers by using of microwave sensor data. Another movement comes from European insurance companies. They have started to operate the trial information service which aims to accelerate the process of claims-paying.