The secrets of soil moisture monitoring via satellite: insights from APOLLO partner Starlab Barcelona SL

APOLLO’s four services are based on cutting-edge technological advances in the field of precision agriculture. The technologies used to develop our services ensure that our users get trustworthy data / advisory services. For this reason, the APOLLO consortium includes SMEs with great experience in precision farming: Starlab Barcelona SL is one of them.

Starlab Barcelona SL is a private company, located in Barcelona, Spain (founded in 2000) and Harwell, UK (2013). With the objective of transforming science into technologies with a significant impact on society, Starlab’s Space department located in Barcelona is continuously developing and improving operational information services using space data with a focus on agriculture, and urban markets. Since its founding, Starlab has been continuously involved in state-of-the-art R&D projects for the European Space Agency and within international industrial consortia.

1. What expertise does STARLAB bring to APOLLO?
In the context of the APOLLO project, Starlab brings its expertise in satellite image processing and particularly on the exploitation of satellite SAR (Synthetic Aperture Radar) data to retrieve information concerning soil moisture in agricultural fields. Our team implements a technology that generates soil moisture maps which, combined with other satellite derived information, enables APOLLO to provide valid products to support farmer’s decisions related to irrigation and tillage scheduling.

2. Which APOLLO services use / are based on your products?
As is well-known, irrigation is one of the most important tasks in agriculture, while also being the major consumer of fresh water globally. Also, tilling the soil when soil moisture is not optimal (i.e. if the soil is either too wet or too dry) requires excessive energy and may damage and/or degrade the soil – with a consequent drop in crop yield. With this in mind, Starlab generates products that enable APOLLO to provide solutions to help all farmers make better decisions. Taking advantage of the free and open Sentinel-1 SAR (Synthetic Aperture Radar) acquisitions, our experts retrieve useful soil moisture information. The high-value products which are made using this information are the main pillars on which two of the six APOLLO services are based: Tillage Scheduling and Irrigation Scheduling.

“Taking advantage of free and open Sentinel-1 SAR (Synthetic Aperture Radar) acquisitions, our experts retrieve useful soil moisture information.”

3. Tell us about how the satellite-based information you provide feeds into these products?
To generate soil moisture maps we exploit the information embedded into the microwave signal reflected back to the SAR antenna of Sentinel-1 satellite. This system is an active sensor that sends a microwave signal to the Earth and receives the returning signal, which is modified after interacting with several targets. The microwave signal of Sentinel-1 is able to penetrate the vegetation canopy and the top soil layer. The effects of such interactions on the returning signal depend mainly on the surface roughness, vegetation cover and soil moisture. In principle, the power of the returning signal is higher for rough surfaces, in the presence of vegetation, and for wetter soils. Based on these assumptions, the model implemented in APOLLO allows understanding the soil moisture conditions from the returning signal received by the Sentinel-1 SAR sensor, from bare soil surfaces but also from cultivated fields.

Map showing soil moisture in a selected cotton field in the pilot of Municipality of Pella, Greece. Soil moisture extracted in 16th June 2017, measured in Volumetric Water Content.

4. Are soil moisture maps available for different types of soil?
Yes. The data is available for different types of soil. For each field, composition of the soil (% clay, sand, and silt) is necessary to compute the soil moisture maps. Small local soil texture variations within the field do not have a significant impact on the final soil moisture product.

5. Are high-resolution soil moisture maps based on satellite data available for all growing stages?
Thanks to the frequent availability of Sentinel-1 acquisitions, the soil moisture model can be used during the whole vegetation cycle. Both Sentinel-1 satellites observe the same area of interest every 2-3 days at European latitudes. Using in situ measurements, we were able to tailor the soil moisture algorithm to various crop categories such as cereals, root crops and cotton, and to bare soil.

6. Can farmers with different field sizes benefit from APOLLO’s soil moisture maps?
Thanks to the high spatial resolution of Sentinel-1 products, we are able to provide a suite of agricultural services specifically designed to address the needs of small farmers, as well as larger cooperatives. The 10m x 10m pixel size of Sentinel-1 images allows for soil moisture maps of different field sizes to be generated, from 1 ha parcels to much larger cultivated areas – without degrading the product’s quality.

“Thanks to the high spatial resolution of Sentinel-1 products, we are able to provide a suite of agricultural services specifically designed to address the needs of small farmers, as well as larger cooperatives.”

7. What other kinds of added value can satellite data provide to farmers and agricultural consultants?
Satellite data provide the inputs for accurate analyses of soil moisture conditions, assessments of vegetation status and forecasts of meteorological conditions. Using satellite data acquired by both SAR, optical and meteorological sensors, we are able to provide frequent information regarding not only soil moisture, but also weather conditions, vegetation status and biomass. The main objective of all farmers is to produce good quality products, increasing the crop yield by minimising costs and efforts. Moreover, there is increasing interest in environmentally sustainable agriculture. The solutions that we propose in APOLLO can help all farmers and agricultural consultants to achieve their goals by helping them develop an efficient schedule of agricultural practices based amongst others on our soil moisture products. These inputs allow the optimum moment to till and irrigate to be identified, and also make it possible to monitor crop growth and estimate yield.