Geodetic Earth Observation

The geodetic works are important for flood management. Especially, Digital Terrain Model (DTM) to design the flow direction and connecting the sub-basin area. The option to gain information on flood risk areas for the works on mapping, design and making a mitigation and adaption plan is mostly exclusively by geodetic measures such as remote sensing, photogrammetry or terrestrial surveying.

6.3.1 TerraSAR-X and TanDEM-X

Herein, the Earth Observation of Germany – the Deutsches Zetrum für Luft und Raumfahrt (DLR) – has developed an intelligent tool called the TanDEM-X mission (TerraSAR-X add-on for Digital Elevation Measurement) which consists of two closely identical earth observation satellites; TerraSAR-X and TanDEM-X (DLR, 2016a).

Figure 6.5 TerraSAR-X and TanDEM-X (DLR, 2016a)³⁵

35 Artist's view of bistatic observation by the TanDEM-X configuration; EADS Astrium

Both are equipped with a powerful modern radar system called Synthetic Aperture Radar (SAR). It permits observing the earth's surface not only in daylight but also when it is obscured by darkness and/or clouds (ibid).

TerraSAR-X has been launched on a Dnepr rocket from the Baikonur cosmodrome in Kazakhstan on June 15, 2007. TanDEM-X was scheduled to follow in the first half of 2010.

From then on, the two satellites fly in formation in their 514 km orbit (ibid).

The TanDEM-X project is a step that logically follows to the international radar missions like X-SAR (X-Band Synthetic Aperture Radar).

Table 6.3 Mission Parameters (DLR, 2016a)

Launch First half of 2010

Site Baikonur, Kasachstan

Mission operating German Space Operations Center, DLR Oberpfaffenhofen Satellite commanding DLR ground station Weilheim

SAR data reception Kiruna (north Sweden), Inuvik (Canada), O'Higgins (Antarctic) Lifetime 5 years, 3 parallel operation with TerraSAR-X

The mission has the goal of generating a global Digital Elevation Model (DEM) with an accuracy corresponding to the DTED-3 specifications (12 m position, 2 m relative height accuracy for flat terrain.

The central region of Thailand is a flat area which is a challenge for the design of an optimum track of the new artificial Chao Phraya River. As a consequence, it is necessary to use data from Digital Elevation Model (DEM) to support the working process.

In addition, not only the TanDEM-X which provides DEM information, but also the EnMap is one of the most useful data for environmental management which is useful for flood management as well. This research will provide brief information about EnMap on which a future research can built on for flood response planning.

In Germany Deutsches Zentrum für Luft- und Raumfahrt (DLR) – German Aerospace Center (Storch et. al., 2017):

1) TanDEM-X – the Earth in three dimensions

2) EnMAP – Germany's hyperspectral satellite for Earth observation

 EnMAP (Environmental Mapping and Analysis Program) will be the first German optical earth remote sensing mission in orbit. It will acquire high quality hyperspectral image data.

 EnMAP may help to find global answers to a range of questions dedicated to environmental, agricultural, land use, water management and geological issues.

Germany's hyperspectral satellite for Earth observation – EnMAP will be launched date in 2017 with a sun-synchronous orbit at a height of 643 km above the Earth, recording data with a 30 x 30 m ground resolution.

Table 6.4 Tandem-X Mission and System requirement (IEEE, 2004)

(See Appendix 3 for additional information)

The benefit of the TanDEM-X data is providing high quality DEM data for this flood research in the scientific sector. The data is designed for getting experience with SRTM. The potential data can fulfil the requirements of a global scale and high-resolution coverage of all land areas together with the vital information for a variety of applications (DLR, 2016b).

As a consequence, for the case study research; the flood height and height of the terrain are in average about 2 m above the sea level and whereas the terrain of the entire Ayutthaya province is ranging from 1 to 7 m and in the Ayutthaya city center and the historical heritage areas from 1 to 4 m. At this point it will be absolutely worth for the new artificial river track design to use the TanDEM-X data provided by DLR

6.3.2 Earth observation system for flood risk information

One example of the DLR working experience in flood risk management is demonstrated in the region of North-Rhein-Westphalia in Germany.

According to Fischer (2016) a thunderstorm occurred in the area of northern France which then moved to the west and also effected the region of North-Rhein-Westphaliain Germany.

People in Münster and Greven were affected by heavy rainfall which started at 1 pm. The rainfall continued for several hours and the measurements which were taken over seven hours showed a precipitation of 292 ltr. /m². In comparison, the average rainfall in that area of the whole year is around 750 ltr. /m². Hence this rainfall had massive impacts.

More than 14,000 households were damaged, the roads were submerged in water and the public infrastructure stopped. All in all, the cost of that disaster is estimated to approximately 80 Million Euro. Two people died in accidents and many others were injured (ibid).

Unfortunately, the statistics prove that these kinds of situations are occurring more likely in the future due to changing weather conditions. Not only will the average rainfall per year increase, but also the probability of severe flash floods. Hence, many organizations are trying to estimate areas which are in high risk to prepare counteractions in these locations.

Existing tools for the simulation of flood situation, e.g. from the insurance sector, can correctly simulate a flood along a river, just by following the rule “the farther away from the river, the better protected from flooding”. But the disaster from Münster showed that these tools cannot calculate the more complex risk in the case of flooding from rainfall (ibid).

Therefore, the insurance sector began to cooperate with the German Aerospace Center (DLR) in the year 2013 with the goal of determining new flood risk zones. The DLR however is not using the insufficient hydrological basis information. The DLR relies on the statistical classification and evaluation of terrain data. The principle is simple, water always flows to the lowest area. By following this rule, even the rainfall data of the area does not have to be considered as well, because the influence of it in this case is fractional. The predictions of the DLR were compared with historical flood data and verified an impressive accurateness.

During the first simulation, the mission of the Earth observation Center (EOC) used data from the Indian “Cartosat-P5-Sattelite”. However, nowadays the DLR has access to the most precise terrain data currently available, which was achieved by their own TanDEM-X mission.

The TanDEM-X mission provided detailed information of the worldwide terrain which offers the possibility of flash flood calculations on global scale (ibid).

The simulation project of the Earth Observation Center ended in October 2015, while shortly after, many organizations showed interest in the results of the study. Since the end of 2016 this system is used to predict risk areas in Germany.

Figure 6.6 Overlay of different Calculation Layers

On the left the Satellite Image in visible light, the Terrain Model in the middle and the Risk Area Calculation on the right (Fischer, 2016).

The new method of risk analysis is not only relevant for insurance organizations, but could also be considered in terms of the planning and design of infrastructure. Furthermore, private households could benefit when those maps are available for free on the internet. Private people could then check if they are in risk and initiate private flood protection measures.

In the meantime, the DLR is using the collected data to develop hazard maps for even more natural disasters such as storms or ground frost. This geo-information has the potential to give valuable information of safe area and areas in risk. That’s why the DLR is working closely together with organizations like insurances which can help to optimize the models.