A first look at Asia with Sentinel-1A satellite imagery

IRRI and partners use remote sensing imagery from satellites to generate information on the rice crop, such as planted area, seasonality, cropping intensity and damaged area due to flood or drought. Information on crop growth from such imagery can also be used in crop growth simulation models to estimate yield.

In recent years we have been working with partners in the RIICE and PRISM projects to develop and test methods for mapping rice using Synthetic Aperture Radar (SAR) imagery. SAR is particularly suited to rice crop mapping and monitoring because of the unique temporal signature of lowland rice which can be extracted from multiple SAR images through the season. SAR systems can penetrate cloud, which is an additional factor in their favour since most rice in Asia is grown in the cloudy monsoon season.

To date, our work has been limited to pilot or test sites due to both the complexity and cost of obtaining and processing SAR images. Due to a long standing collaboration with sarmap, the “complexity” part of the problem has been addressed through the development of automated processing chains which can be run locally or hosted on cloud computing facilities. The “cost” part of the problem also recently changed. The European Space Agency launched the Sentinel-1A satellite in 2014 and it will become a major source of SAR imagery from 2015 onwards, and will be joined in 2016/17 by Sentinel-1B. Sentinel-1 data is freely available and will cover many of the rice-growing areas of Asia with a spatial resolution of 20 metres.

As a demonstration of the potential of the Sentinel program, sarmap and IRRI have generated mosaics composed from many Sentinel-1A images that cover 7 million square kilometers of South and South East Asia. These cloud free mosaics show the value of SAR imagery for detailed monitoring of agriculture and natural resources across Asia.

The mosaics are composed of images taken during February and March 2015. SAR imagery must be interpreted differently to imagery commonly seen in Google Maps and other mapping services. In these mosaics, we have processed images such that dark blue represents water or other flat surfaces such as airport runways, orange and white represent built up areas and human settlements, light blue represents bare soil, while brown and green show vegetation at different stages of growth.

The mosaics are a snapshot of the earth’s surface, and have not been interpreted for rice mapping purposes. Sentinel-1A will continue to acquire images over the region, and these images will become increasingly useful as they reveal the progress of the rice crop over time, season after season. The ESA Sentinel program has a big role to play in the future of satellite-based remote sensing for rice crop applications.

These mosaics are available for viewing as online maps or can be downloaded and viewed in Google Earth.

Philippines Sentinel 1A mosaic thumbPhilippines Sentinel 1A mosaic created with Mapscape-RICE
©Copernicus data (2015)
You can download the kml files for this map here.
Java-Sentinel-1A-mosaic-thumbJava Sentinel 1A mosaic created with Mapscape-RICE
©Copernicus data (2015)
You can download the kml files for this map here.
Thailand-Cambodia-Laos-Sentinel-1A-mosaic-thumbThailand, Cambodia, Laos Sentinel 1A mosaic
created with Mapscape-RICE ©Copernicus data (2015)
You can download the kml files for this map here.
Myanmar-Sentinel-1A-mosaic-thumbMyanmar Sentinel 1A mosaic created with Mapscape-RICE
©Copernicus data (2015)
You can download the kml files for this map here.
South-Asia-Sentinel-1A-mosaic-thumbSouth Asia Sentinel 1A mosaic created with Mapscape-RICE
©Copernicus data (2015)
You can download the kml files for this map here.