Elevation Data is needed to protect Europe’s coastal zones from the global warming changes!

According to the United Nations climate panel a global average temperature rise in between 1.8- 4.5 degrees C [1] between the years 2000 to 2100 is expected. A corresponding global average sea water level rise in the range of 0.18 to 0.58 m is expected during the same period [2]. Further on the climate change leads to more variance in the climate and more extreme weather conditions, including dramatically higher maximum high water levels, storms and hurricanes. The increasing water levels have a major impact on the coastal zone. Coastal erosion caused by increasing average water levels is already today a major problem around the world. In addition the maximum high water levels and extreme weather conditions is a threat to major cities and other large infrastructural investments.

For example in Sweden, the 100 year maximum high water level is expected to rise in between 0.4-1.4m in the northern part and in between 0.8-1.8m in the southern part [3] (the difference mainly depends on land uplift affecting northern Sweden). A rule of thumb in areas affected by coastal erosion is that an average sea water level rice of 1m cases about 100 m erosion of the shoreline. According to the Swedish Geological Institute 12% of the Swedish real estate buildings are located within less than 100 m from the shore [4] and are hence in the risk area.

Stockholm, the capital of Sweden, is located nearby the Baltic sea and the lake Mälaren. During the latest maximum high water conditions in December 2000 it was only a few centimetres marginal for the subway to be flooded in central Stockholm. The 100 year expected maximum high water conditions, taken in consideration the increasing water levels, would according to Swedish geological institute not only flood the subway but also 840,000 square meter of building area in central Stockholm.  

The situation is similar in several other places in the world. In addition a single extreme weather event can literally change a region’s economical situation dramatically over night. One example of this is the hurricane Cathrina in the US.

In order to protect the near shore infrastructural investments, geographical elevation data is needed. Without the detailed knowledge of the topography it is impossible to identify risk areas, to model and simulate the changes and to plan preventive actions. Also elevation data of the sea floor is needed, since the sea floor conditions have major impact on wave heights and on coastal erosion conditions. However, the access to detailed elevation data is limited. Going back to the example of Sweden, the accuracy of the national elevation database is 2.5m on land, which is not by far accurate enough for performing any planning in the coastal region. Even though the important waterways are well surveyed in Sweden, most other seabed areas are based on lead line surveys made early last century. Especially, there is a lack of modern data in the shallow water near shore areas, where the costs of traditional boat surveys are high.

A modern tool for collecting large datasets of topographic and bathymetric elevation data in the coastal region is Airborne LIDAR Bathymetry.  LIDAR is an abbreviation for Light Detection and Ranging, and LIDAR systems utilises laser light emissions for measuring distances. A short laser pulse is sent from the airborne system towards the land or the water surface. On land the light is reflected partly on the canopy, partly on the ground. At sea the light is partly reflected on the water surface and some light penetrates the surface and is reflected on the sea floor. The reflections are collected by the airborne LIDAR system optics and converted to digital signals in the system receivers.  The distance can be calculated from the time elapsed from the laser pulse was sent until the laser pulse was received (by use of speed of light in air and in water).

During a mission the LIDAR system scans over the land and see, such that an area is covered. Accurate sensors in the LIDAR system record the distance and the direction of each received laser pulse.

The position of the LIDAR sensor itself is derived from an internal accurate navigation system using both GPS and inertia navigation to derive a few centimetre accuracy positioning of flight trajectory. The accuracy is achieved after post-processing of the data, using GPS reference stations to eliminate position errors in the GPS system and advanced backwards and forward calculating algorithms to calculate the correct actual flight trajectory.

Modern coastal LIDAR survey systems are capable to measure both land and sea floor simultaneously from a single flight line. The accuracy of the elevation data is typically 15 cm rms on land and 25 rms on sea floor after post processing and quality assurance procedures. In addition the systems collect digital images used for geo-referenced ortho photo mosaic production. The last year’s developments have further resulted in algorithms determination of sea floor reflectance, sea floor roughness, and optical parameters in the water volume from bathymetric LIDAR data. Such parameters can be used for environmental investigations such as sea bed classification, sea bed habitat investigations and water pollution.

Compared to traditional boat surveys for collection of bathymetric elevation data, Airborne LIDAR systems are very competitive for capturing very large datasets in relatively shallow waters. An airborne bathymetric LIDAR system can collect up to 250 square km of data per day for coastal management purpose, or up to 125 square km per day if the data shall be used for bathymetric charting. The efficiency of Boat survey decreases with decreased depth, and it is about 10 times more expensive to survey at 2 meters depth than at 10 meters depth. For an airborne system the survey costs are independent of depths, up to the maximum depth penetration which typical is about 2.5 x the sight depth in the water. Hence, even if some contingency has to be considered using LIDAR bathymetry due to weather constraints, LIDAR bathymetry is a very cost efficient tool.

In the United States there is a major National Coastal Mapping Program ongoing since several years. In this program the complete US coasts including the great lakes is surveyed in 8 years cycles. Data is captured from at least 500 m inland to 1 km offshore (more in complex coastal regions) by use of Airborne LIDAR bathymetry as the prime sensor.

The program is organised by the Joint Airborne LIDAR Bathymetry Center of Expertise (JALBTCX) http://shoals.sam.usace.army.mil/ , a partnership between US Army Corps of Engineers (USACE) http://www.usace.army.mil/ , the US Naval Oceanographic Office (NAVOCEANO) http://www.usace.army.mil/  , and the National Oceanic and Atmospheric Administration (NOAA) http://www.noaa.gov/ .

JALBTCX collects and processes yearly about 3600 km of coastline per year, by using their own sensor and by use of sub-contracted sensors. The data is made available by internet via NOAA’s Coastal Service Center http://maps.csc.noaa.gov/TCM/.

The US National Coastal Mapping program supports the environmental, social and economic well being of the coast by provision of high quality data to the community. The primary users of the data is state and regional coastal resource managers, who are at the forefront of the nation’s effort to preserve coastal resources, promote responsible developments, implement best practices, and build capacity to respond and recover from coastal hazards. In addition the data is used by research institutes, non-profit and private companies for various issues.

The following products are delivered

• ASCII XYZ data – Post processed data in Longitude, Latitude and Elevation in the ellipsoid coordinate system and /or in the geodetic coordinate system.
• Digital Elevation Models – Digital elevation models derived from the xyz data delivered in the Geo-TIFF format, directly importable in ESRI ArcMap. Models are created both for bare earth elevations (ground below building and vegetation) and surface elevation models including buildings and the canopy.
• Building footprints – Buildings footprints are derived in the data post processing procedure and the footprints polygons are delivered in the ESRI shape file format.
• Ortho Mosaic Images – Ortho rectified mosaic RGB images, delivered in TIFF file format.
• Pseudo reflectance – Reflectance images of sea floor delivered in GEO TIFF file format
• Shoreline vector – Vector of shoreline delivered in the ESRI Shapefile format

LIDAR bathymetry has also been evaluated and to some extent used in Europe. A major ongoing initiative is made by the Irish seabed survey, the INFOMAR project http://www.gsi.ie/Programmes/Marine/INFOMAR.htm where bathymetric LIDAR is used for surveying shallow areas of the sea-floor. The Infomar project is organised by Geological Survey of Ireland http://www.gsi.ie/ and Marine Institute  http://www.marine.ie/home/ . Bathymetric LIDAR has been evaluated by the Litto 3D project in France http://www.littoral.ifen.fr/Le-projet-Litto-3D.186.0.html . Several tests with bathymetric LIDAR has also been performed by IFREMER in France http://www.ifremer.fr/francais/index.php. In Spain the bathymetric LIDAR has been evaluated for Coastal Erosion applications by Institute Cartografic de Catalunya http://www.icc.es/web/content/en/common/icc/inici_icc_ciutada.html . The United Kingdom Hydrographic Office http://www.ukho.gov.uk/  has made several trials to evaluate bathymetric LIDAR for charting purpose. In addition bathymetric LIDAR projects have been performed in Germany, Norway, Estonia, Italy, Poland and Denmark.

Sweden was very early in the usage of bathymetric LIDAR systems, and had two systems in operation already in the mid 1990:s. However those LIDAR systems were primary developed for submarine hunting in shallow waters and had not by far the same capacity for coastal surveys as the modern bathymetric LIDAR systems today. In any case a lot of experience was collected by the Swedish maritime administration http://www.sjofartsverket.se/default____603.aspx, the Swedish Navy and the Swedish Defence Research Agency from this period. Recently several minor trials with modern bathymetric LIDAR systems have been made. The investments made by the Swedish maritime administration and the Swedish navy have been the foundation for the bathymetric LIDAR knowledge in Europe.

References:
[1] Source: United Nations climate panel
[2] Source: United Nations climate panel.
[3] Source: Swedish governmental investigation “Klimat och sårbarhetsutredningen”
[4] Source: Swedish geological institute