Small Sea Salinity & Satellite Navigation Irrigation

Artists impression of the Soil Moisture and Ocean Salinity (SMOS) satellite. Image courtesy of ESA – P. Carril.

A couple of interesting articles came out in the last week relating to ESA’s Soil Moisture and Ocean Salinity (SMOS) mission. It caught our attention, as we’re currently knee deep in SMOS data at the moment, due to the soil moisture work we’re undertaking.

SMOS was launched in November 2009 and uses the interferometry technique to make worldwide observations of soil moisture over land and salinity over the ocean. Although its data has also been used to measure floating ice and calculate crop-yield forecasts.

The satellite carries the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) instrument, which is a 2D interferometric L-band radiometer with 69 antenna receivers distributed on a Y-shaped deployable antenna array. It has a temporal resolution of three days, with a spatial resolution of around 50 km.

A recent ESA article once again showed the versatility of SMOS, reporting that it was being used to measure the salinity in smaller seas, such as the Mediterranean. This was never an anticipated outcome due to radio interference and the land-sea boundary contamination – where the land and ocean data can’t be distinguished sufficiently to provide high quality measurements.

However, the interference has been reduced by shutting down illegal transmitters interrupting the SMOS signal and the land-sea contamination has been reduced by work at the Barcelona Expert Centre to change the data processing methodology.

All of this has meant that it’s possible to use SMOS to look at how water flows in and out of these smaller seas, and impact on the open oceans. This will help complement the understanding being gained from SMOS on ocean climate change, ocean acidification and the El Niño effect.

A fascinating second article described a new methodology for measuring soil moisture using reflected satellite navigation signals. The idea was originally from ESA engineer Manuel Martin-Neira, who worked on SMOS – which we accept is a bit more of a tenuous link, but we think it works for the blog! Manuel proposed using satellite navigation microwave signals to measure terrestrial features such as the topography of oceans.

This idea was further developed by former ESA employee Javier Marti, and his company Divirod, and they have created a product to try and reduce the overuse of irrigation. According to Javier, the system compares reflected and direct satnav signals to reveal the moisture content of soil and crops and could save around 30% of water and energy costs, and improve crop yields by 10-12%. It is a different methodology to SMOS, but the outcome is the same. The work is currently been tested with farmers around the Ogallala aquifer in America.

For anyone working in soil moisture, this is an interesting idea and shows what a fast moving field remote sensing is with new approaches and products being developed all the time.