The Smos spacecraft senses the wetness of soils, and its unique instrument has detailed how the earth became saturated in the monsoon rains.
The floods, which began more than two weeks ago in the mountainous northwest, are the worst in recorded history. Some 20 million people and 160,000 sq km of land – a fifth of the country – have been affected by the disaster. Data from the European Space Agency’s new Smos satellite has been processed to make a series of maps.
The four snapshots featured at the top of this page run from 17 July to 4 August. They show the ground getting progressively wetter, indicated by the shift from warmer (yellow/orange) to cooler (blue/grey) colours. The consistent blue in the south reflects the naturally wetter landscape that surrounds the Indus River where it enters the Arabian Sea. Smos is a scientific satellite that is pioneering a novel Earth observation technique.
It carries an 8m-wide interferometric radiometer that senses the natural emission of microwaves coming up off the planet’s surface. Variations in the sogginess of the soil will modify this signal. Satellite data is frequently used in the relief response to major disasters, and in the case of Pakistan the world’s satellite fleets were mobilised on 2 August to provide space-borne information under the International Charter [on] Space and Disasters.
The charter was activated by US Office of Foreign Disaster Assistance. Radar data, in particular, is used to identify the presence and extent of floodwater. But there is an expectation that once the Smos observation technique has become sufficiently mature, it too will be able to play a leading role in disaster mitigation.
By identifying the soils closest to saturation, the satellite would provide advance warning on which areas in a flood-stricken region were likely to flood next if weather conditions failed to improve and rains continued to fall. Dr Claire Gruhier is a Smos researcher from Cesbio in Toulouse, France. She told BBC News the results were preliminary: “What we show is not the flood area; what we show is the water content in the soil. So, it is not exactly the same information. But our maps are very consistent with the flood-affected areas in Pakistan revealed by other satellites.”
Smos principal investigator, Dr Yann Kerr, added: “I am quite confident that in a few months when the calibration and validation is [completed on Smos] and the algorithms are fine tuned, we will be able to infer also the extent of the actual floods. Smos is less accurate than optical/radar sensors, no question; but it is all-weather and sees any point of the globe in less than two days.”
The Smos team is particularly encouraged to have got good results out of a mountainous area, a type of terrain from which it is harder to retrieve soil moisture values from space.
The Smos satellite was launched in November last year, since when it has been going through a commissioning phase. Fully processed data products are due to be released to the world’s scientific community next month.
As well as studying soil moisture, the spacecraft’s instrument can also sense changes in salinity in ocean water.