Through satellites by the European Space Agency (ESA) and other providers, RIICE is scanning the earth surface in Southeast Asia using radar-based remote sensing technology. This technology has the ability to detect and interpret change on the earth’s surface without direct observation. Depending on the satellites and the sensors used, the remote sensing data can have a spatial resolution of only several meters (20 by 5 meters for the ESA’s Sentinel programme) and a temporal resolution of several days (i.e. the satellite can take data from the same spot every few days as it circles the earth).
(Image: ESA / Pierre Carril)
What is radar-based remote sensing?
Radar-based remote sensing, also called Synthetic Aperture Radar (SAR), collects information on the earth's surface by emitting energy in order to scan objects and areas whereupon a sensor then detects and measures the radiation that is reflected or backscattered from the target. Radar-based remote sensing technology measures the time delay between emission and return, establishing the location, height, speed and direction of an object.
The microwave sensors of radar-based, space-borne earth observation offer hence an effective alternative to optical observation which has a major disadvantage of clouds often obstructing the earth observation.
By analysing time series, radar-based remote sensing technology can determine the extent of rice cropping, monitor the rice growth, estimate (to some extent) biomass and identify crop damages and losses caused by droughts and floods.
Remote sensing also replaces costly and slow data collection on the ground which was often found to be inaccurate or even manipulated.
How can remote sensing observe crop growth over time?
The basic idea behind the generation of rice acreage using SAR techniques is the analysis of changes in the acquired data over time. Measurement of temporal changes in reflectivity of the plants relates to the phenological status of the rice: an increase in the radar backscatter corresponds to a growth in the rice plants. In fact, the radar response to rice fields at different growing stages during the crop cycle can be distinguished in three main growing stages, namely sowing-transplanting (surface scattering), growing (surface-volume scattering) and flowering (volume scattering).
Actual rice-growing seasons observed in Bangladesh:
2011 - First season, start of season (below left); Second season, start of season (below right)
2011 - First season, peak of season (below left); Second season, peak of season (below right)
How precise can remote sensing map rice areas?
Is radar-based remote sensing better than optical remote sensing?
Synthetic Aperture Radar (SAR) is an active remote sensing system. An antenna, mounted on a platform, transmits a radar signal in a side-looking direction towards the Earth's surface. The reflected signal is backscattered from the surface and received a fraction of a second later at the same antenna.
Spaceborne SAR sensors offer hence an effective alternative to optical observation which has a major disadvantage of clouds often obstructing the mapping and monitoring.
Is remote sensing a new technology?
While earth observation from space is a recent matter, pigeon photography as an aerial photography technique was invented in 1907 by the German apothecary, Julius Neubronner, who also used pigeons to deliver medications. A homing pigeon was fitted with an aluminum breast harness to which a lightweight time-delayed miniature camera could be attached. Later, this technique was not only used in the art context but also by the military.