Satellite delivers images of soil moisture and ocean salinity

First images of soil moisture and ocean salinity
by Aine Gormley
for ASTRONOMY NOW
Posted: 2 March 2010

The first images delivered by the European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) mission show global variations in Earth's soil moisture and ocean salinity.

SMOS will play a key role in monitoring climate change on a global scale by helping to improve weather and climate models. It is the first satellite that enables passive surveying of the water cycle between oceans, the atmosphere and land.

Snapshot of ScandinaviaÕs brightness temperature. Image: ESA.

The SMOS Earth Explorer satellite effectively captures the ‘brightness temperature’ – a measure of the radiation emitted from Earth – to generate the images. The moisture content of the soil and salt content of surface ocean waters can be drawn from these images. Bodies of water show up as cold spots because they have low brightness temperatures. Dry soils are indicated by high brightness temperatures.

ESA have been improving the quality of the brightness temperature images since the Earth Explorer satellite was launched into orbit in November 2009 from northern Russia. They will continue to commission the satellite until the end of April 2010. This commissioning phase involves testing the system that sends the data to the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) instrument for calibration. MIRAS gives a snapshot of brightness temperature every 1.2 seconds.

Achim Hahne, ESA’s SMOS Project Manager, says, “We are only half-way through the in-orbit commissioning phase and it is rewarding to see these first very promising calibrated products delivered by SMOS.”

The calibration process ensures the instrument meets required performance and corrects for error, such as when light is reflected by the Sun and Moon. In the uncalibrated image of Australia (left), lakes are invisible, but in the calibrated one (right) they are visible. Image: ESA.

Suzanne Mecklenburg, ESA’s SMOS Mission Manager, adds, “It is exciting to see these first data products, which are already of excellent quality, even though we haven’t completed all the calibration activities yet. We also had very positive feedback from the scientists who have already started using the data.”

Jordi Font, the mission’s Lead Investigator for ocean salinity, comments, “For the ocean products, a lot of work still has to be done before the release of operational data. The low sensitivity to variations in salinity requires very accurate instrument calibration and data processing to achieve the mission’s measurement goals for ocean salinity.”

In this image showing Brazil, the Amazon River is seen in lower brightness temperatures than the rainforest. Image: ESA.

A validation campaign to compare in situ measurements with those taken by the satellite is underway in Australia. Extensive airborne campaigns will also be carried out by Germany, Spain and France in the spring.