Why is it important?

Remote sensing technology can provide systematic and cost-effective information of the marine and coastal environment at large scales.

This is of interest to public authorities, looking to further increase the effectiveness of national monitoring programs through the inclusion of novel technology.

Project highlights:

Assessing the potential use of air and spaceborne remote sensing technologies for monitoring submerged aquatic vegetation in the nearshore coastal zone of Danish waters

Mapping the distribution of benthic habitats to expand the knowledge about e.g. eelgrass area coverage as an indicator for water quality status

Evaluating the use of Sentinel 2 and 3 satellites for monitoring surface chlorophyll concentration to improve the temporal resolution and the spatial distribution of the current water quality monitoring program

In more detail..

The Danish Environmental Protection Agency initiated a 2-year activity in 2017, where DHI GRAS was in charge of satellite analyses of water quality and benthic habitat mapping for selected Danish water areas.

We examined the potential for using remote sensing technologies in connection with the current Danish national NOVANA (National Monitoring and Assessment Programme for the Aquatic and Terrestrial Environment) monitoring program.

The first part of the project looked at the distribution of eelgrass using data from the Sentinel-2 satellites. Eelgrass is an important water quality indicator and has been included in the Danish water plans to assess the environmental state along the Danish coasts. The eelgrass distribution reflects the clarity of water and nutrient richness and thereby indirectly the quality of the water.

The most common practice for mapping eelgrass meadows is to record the distribution along a transect line with a diver, which is costly and unsuitable to derive the complete temporal and spatial eelgrass cover of the Danish coastal waters.

An updated nationwide map of the eelgrass distribution therefore has several potential uses in the Danish water plans:

1) For further development of eelgrass as an indicator of the coastal areas' condition

2) In connection with land-use planning and concrete protection of eelgrass meadows

3) For quantification of eelgrass's ecosystem services

The second part of the project looked at the chlorophyll concentrations in the Danish surface waters using data from Sentinel-2 and Sentinel-3 satellites.

Chlorophyll concentrations are regularly determined by a chemical analysis of water samples which are collected from a ship and subsequently undergone trial processing in the laboratory. Because this type of traditional sampling is costly, usually measurements are taken at only 1 location per water area, approximately every 14 days.

This limits the ability to document the spread and temporal dynamics of important events such as algae blooms and leads to relatively large deviations in seasonal means.

The combination of Sentinel-2 and Sentinel-3 provided a cost-effective way to supplement national in-situ monitoring of surface chlorophyll in the shallow Danish coastal waters, in order to improve the temporal and spatial distribution of chlorophyll concentration.

Satellite technology cannot replace in-situ sampling completely, but it can optimise sampling design and fill gaps.

By bringing together information from various sources, the confidence in the data can be enhanced and greatly improve national assessments.

Chlorophyll summer mean 2018 from Sentinel-3 for Roskilde Fjord and Isefjord.

The Danish Environmental Protection Agency:

EPA is the authority in charge of preparing legislation, granting authorisations and providing guidelines within the fields of the environment and health: chemicals, pesticides, gene technology, soil, waste and environmental technology.

The range of tasks is broad, from algae bloom detection and regulations for chemicals in hair colourants, through investigations into how more waste can be recycled and authorisations for new pesticides to the handling of fruit and vegetables.

Monitoring agricultural fields

DHI GRAS A/S

gras@dhigroup.com
+45 4516 9100

Agern Alle 5,
2970 Hørsholm,
Denmark

CVR: 25621646