SMOS Instrument Principal Engineer: interview with Manuel Martin-Neira

Martin-Neira, a Spanish national, joined ESA’s European Space Research and Technology Centre (ESTEC) in the Netherlands in 1988 as Young Graduate Trainee to work on microwave radiometry. He then worked in industry but rejoined ESA in 1992 to work in the Technical Directorate where he initiated the development of technologies and innovative concepts for remote sensing instruments, one of them being MIRAS. He was nominated to provide functional support to the SMOS project in 2002.

He obtained his MSc and PhD in Telecommunications Engineering at the Polytechnic University of Catalonia, Barcelona, Spain.

ESA: SMOS is adopting a new technique to observe soil moisture and ocean salinity – can you explain how this works?

Manuel Martin-Neira

Until now, microwave radiometers have used ‘large scanning’ antennas to generate an image. ‘Large’ to obtain fine spatial resolution and ‘scanning’ to image a wide strip of the ground along the satellite flight path. However, using low frequencies such as L-band, which are needed for specific applications, would normally need huge antennas, and this means that mechanical steering becomes a real challenge. SMOS adopts a radically different approach to solving this problem – we use small antenna elements with a wide field-of-view to provide the required area coverage. The interferometric processing of all the signals from the antennas achieves the fine spatial resolution required, all without any mechanical scanning.

ESA: What advantages are there by measuring at L-band?

Manuel Martin-Neira

The advantage of the L-band is that the atmosphere is transparent at these frequencies, allowing the surface of Earth to be probed. Moreover, thermal emission at L-band has a stronger dependence on the geophysical parameters of the amount of water in the soil and salt in the oceans, than the emission at other frequency bands.

The portion of the L-band that SMOS observes in – from 1400 to 1427 MHz – is reserved for passive observations by international radio regulations. Such protection is of extreme importance for missions such as SMOS, which carry very sensitive receivers. Any manmade signal could be misinterpreted as a variation in the geophysical parameters.

ESA: What have been the biggest technical challenges developing the SMOS mission?

Manuel Martin-Neira

The first challenge was to produce several tens of light-weight and cost-effective microwave receivers with very similar electrical characteristics. Secondly, it was a challenge to fit a large amount of high-speed correlators into a digital correlator unit to perform the core interferometric processing on board. If we hadn’t achieved this, the data rate to the ground would have been prohibitive.

It was also a challenge to develop the first ‘optical harness’ that ESA will fly into space. This is needed to transport data signals between the receivers and the correlators without generating any electrical noise that would ruin the performance of this ultra-sensitive instrument.

Lastly, the development of the simple arm deployment concept, which is based on spring-loaded motors and is an extremely stable light-weight structure, posed a challenge. The receivers and correlators flying on SMOS are of third generation, and the optical harness, mechanisms and structure are of second generation.

In parallel to all this, it was the challenge to develop the theory behind this novel instrument and the calibration techniques that will successfully lead to images of the required quality.

ESA: Are there any other Earth observation satellites measuring soil moisture and ocean salinity?

Manuel Martin-Neira

There is currently no mission dedicated to measuring either soil moisture or ocean salinity. Nonetheless, soil moisture products are currently derived from other satellite sensors, both passive (radiometers) and active (scatterometers and synthetic aperture radars). There have also been some very limited retrievals of sea-surface salinity using higher frequency radiometers. However, it is believed that the greater sensitivity to soil moisture and ocean salinity of an L-band radiometer will make SMOS observations the most accurate ones to date.

ESA: What has been the most rewarding aspect of developing the SMOS mission?

Manuel Martin-Neira

Ultimately, to see the mission through from beginning to end. It has also been rewarding for several other reasons. Having the opportunity to work with international, young graduate and Spanish trainees, stagiaires and research fellows, from the very beginning of the development was rewarding. They made important contributions in several areas and helped define what SMOS is today. In addition, I have felt truly supported by colleagues across the world, from Japan to US, and from China to ESA’s Member States.

Participating in the development of the theoretical background, bridging radio astronomy and microwave circuit theory through the ‘Corbella’ equation, named after its author, Professor Corbella from the Universitat Politècnica de Catalunya, was also very rewarding.

It has been a joy to work with competent and enthusiastic industrial partners over the years and the extraordinary and terrific SMOS project team here at ESA. It is also wonderful that scientists have placed so much interest and hope in SMOS and our joint work together has realised a valuable mission. Finally, it is very rewarding to have the recognition I have always received from many colleagues and my bosses at ESA.

ESA: Will you still be involved in the mission once the satellite is in orbit delivering data?

Manuel Martin-Neira

I will be involved in SMOS until the end of the commissioning phase when we will perform a preliminary evaluation of the mission’s performance. Then, together with the scientists, we will decide about the worthiness of proposing a follow-on ‘SMOSops’ operational mission. Such a mission should ensure continuity of soil moisture and ocean salinity observations for further 10-15 years after SMOS.

ESA: Where will you be for launch?

Manuel Martin-Neira

I will be at ESA-ESAC in Madrid. This is where we will be receiving and processing the scientific data for the SMOS mission.

Editor's note:

This is one in a series of interviews with a few of the key people involved in the SMOS mission. Please check back, as the list will be added to over the coming weeks.