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Feature Article

DEIMOS-1 Satellite Provides Imagery for Coastal Management
High Spatial Resolution Satellite Measures River Plume Dynamics, Wetland Flood Levels and Intertidal Vegetation Changes in Spain

AUTHORS:
Isabel Caballero
Ph.D. Student
Edward P. Morris
Postdoctoral Researcher, Ph.D.
Gabriel Navarro
Research Assistant, Ph.D.
Department of Ecology and Coastal Management
Instituto de Ciencias Marinas de Andalucía Consejo Superior de Investigaciones Científicas (ICMAN-CSIC)
Puerto Real, Spain

Satellite-borne sensors are an ideal tool for remotely assessing a number of water quality parameters that determine the functioning of aquatic ecosystems. For example, chlorophyll and total suspended solids in a body of water are critical variables for determining primary production and can help characterize nutrient loading and sediment dynamics. Remote sensing can also potentially provide a synoptic view of the transport of waterborne materials by tides, river discharges and currents, allowing the examination of the role of coastal hydrodynamics in erosion and deposition processes, phytoplankton primary production and the transport of nutrients and pollutants.

In recent years, there have been significant advances in the availability of satellite sensors that can provide frequent high spatial resolution and extensive coverage of environmental parameters in coastal areas. These capabilities offer a substantial advantage over traditional in-situ observations, which often have limited spatial or temporal coverage and are usually expensive. Hence, remote sensing promises to be a cost-effective technique for monitoring coastal dynamics and fulfilling the monitoring obligations of management agencies, such as the EU Water Framework Directive.

One particular new satellite, DEIMOS-1, is used to study coastal processes in the Gulf of Cádiz. The authors present three examples of how DEIMOS-1 images can be used for coastal management in areas with high ecological value: determining the dynamics of a river plume near a fisheries reserve in the estuary of the Guadalquivir River; measuring flood dynamics in the wetlands of Doñana National Park; and tracking changes in intertidal vegetation at Cádiz Bay Natural Park.

An RGB image captured from NASA’s MODIS satellite is shown in (a). An RGB composite from the DEIMOS-1 satellite (b) and a map of TSS concentration at the river mouth defined by band ratio green-red radiances, (c), is shown in a scene captured in March 2011.

DEIMOS-1 Satellite
Developed by Elecnor Deimos Imaging S.L. (Valladolid, Spain), DEIMOS-1 is the first private satellite in Europe that carries a multichannel optical sensor. The satellite is a small automatic spatial platform weighing only 100 kilograms and provides visible and near-infrared (NIR) images split into three wide bands between 510 and 906 nanometers. Designed to obtain terrestrial images, the satellite has a 22-meter spatial resolution that is suitable for studying vegetation cover and a 600-kilometer extent that allows repeated views of an area at a high temporal resolution.

The coordinate system of the satellite imagery was World Geodetic System 1984 UTM zone 29N. Three bands were available per image: Band 3 (green: 510 to 618 nanometers), Band 2 (red: 614 to 698 nanometers) and Band 1 (NIR: 755 to 906 nanometers). The RGB images for the DEIMOS-1 sensor were composed by merging the three bands.


Guadalquivir River Plume Dynamics
In order to study the spatial dynamics of the river plume of the Guadalquivir estuary, eight DEIMOS-1 images were compared to field measurements of the concentration of milligrams of total suspended solids (TSS) per liter, taken using the gravimetric method.

Water samples were collected in three field campaigns at 20 positions in the region of the river mouth within 30 minutes of DEIMOS-1 satellite overpasses. Sampling positions were recorded with a GPS (accuracy within 5 meters).

Water-leaving radiance was extracted from the images at the corresponding positions and compared to the measured TSS. The band ratio, green-red (GR), gave the strongest linear relationship with TSS, where TSS = -639.46 + 2930 GR. The coefficient of determination of this linear relationship is 0.90 (r2), where the Pearson product-moment correlation coefficient is p < 0.001, and the authors used 55 for in-situ data (n = 55).

The high coefficient of determination (r2) suggests that this simple radiance band ratio can determine water sediment loads with a relatively high accuracy. Thus, in areas affected by river runoff, remote sensing may provide a cost-effective alternative for monitoring water quality.

This algorithm was used to calculate TSS of the Guadalquivir River plume after an extended period of heavy rains. The high spatial resolution of the DEIMOS-1 sensor and the GR band ratio’s sensitivity to TSS allows the visualization of detailed structure within the plume.

The most intense water sediment loads were observed in the final stretch of the river, which is surrounded by wetlands. Sediment dispersion and the irregular shape of the plume, caused by the prevailing coastal hydrodynamics, were clearly visible. Therefore, DEIMOS-1 images could potentially provide detailed information on estuarine sediment loads.

Regular synoptic observations of the intensity and structure of river runoff in a range of meteorological and oceanographic conditions will improve researchers’ understanding of coastal sediment dynamics and contribute to the effective management of transitional waters.

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Isabel Caballero is a marine science graduate student and is pursuing her Ph.D. at the Instituto de Ciencias Marinas de Andalucía Consejo Superior de Investigaciones Científicas (ICMAN-CSIC) with support from the Regional Government of Andalucía. Her research focuses on applying remote sensing techniques to study coastal processes.

Edward P. Morris received his Ph.D. in oceanography and marine biology from the University of Groningen in May 2005. Since 2005, he has been a postdoctoral researcher at the University of Cádiz’s biology department. Since September 2011, he has been based in the Department of Ecology and Coastal Management at ICMAN-CSIC.

Gabriel Navarro received a Ph.D. in marine science from the University of Cádiz in 2004. Since June 2005, he has been a research assistant and remote sensing specialist at the Department of Ecology and Coastal Management at ICMAN-CSIC.





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