Satellites assist planners preventing floods (Forwarded)

ESA News
http://www.esa.int

27 November 2003

Satellites assist planners preventing floods

Virtual floods modelled inside computers are an increasingly useful means for 
authorities to prepare for genuine river surges. With flooding classed as the 
world's most costly natural hazard, an ESA project has assessed using satellite 
imagery to improve flood simulation models.

Flood control and management represents a major challenge for water authorities, 
and as the global incidence of flooding increases, it has also become a subject 
of concern for the global insurance industry.

The US Geological Survey estimates that flooding is the world's most costly type 
of natural disaster, costing Euro 170 billion ($200 billion) between 1991 and 
1995. Last year's European floods alone are reported to have caused more than 
Euro 7 billion of damage.

Like everything linked to the weather, floods are difficult to predict -- a few 
days of steady rainfall might be sufficient for a river to burst its banks.

What software-based flood simulation models can do is foretell how a river will 
behave if it does flood, and allow authorities to assess their best course of 
action.

"Here in Flanders, we are responsible for maintaining our many rivers and 
waterways, and are also tasked with preventing or controlling floods," explained 
Project Engineer Ingrid Boey of the Flemish Water Authority AWZ, end user for 
ESA's FAME (Flood risk and damage Assessment using Modelling and Earth 
observation techniques) project.

"A useful research technique for us is by creating hydrodynamic simulations of 
our various river basins. Originally these were physical scale models -- we 
still have those -- but numerical models running in computers are increasingly 
important. We can use them to see what actions should be taken in particular 
scenarios, such as employing controlled flooding areas, locally raising dikes 
higher, activating pumping stations or -- in extreme situations -- ordering 
evacuations.

"From next year our models are going to used operationally to make predictions 
in real time, so it is vital we are sure they are as close to the real world as 
possible."

The problem comes in converting what are essentially one-dimensional computer 
models of water levels and flow into accurate depictions of the two-dimensional 
spatial extent of flooded areas. And when it comes to checking the models 
against historical floods, fully accurate spatial and temporal records can be 
hard to find.

"We find water levels have been recorded, but not always the full spatial 
extent," explained Boey. "Aerial photos are often not available, and even when 
they are, they don't always cover the whole of the flooded area. Also needed are 
hard facts on the duration of the flood. We end up with one person remembering 
three days, and one person recalling two."

The idea behind the FAME project was to use satellite data as an additional 
means of mapping flood extent in zones close to rivers as well as creating more 
accurate flood risk maps and carrying out post-flood damage assessment. Project 
partners included SADL (Spatial Applications Division Leuven), Sarmap and 
D'Appolonia.

Project manager was Professor Patrick Willems of the University of Leuven's 
Hydraulics Laboratory: "Our lab oversees the creation of flood control models, 
so I came at the problem more from the side of the user than the service 
provider. We focused on two flood-prone rivers, the Dender and the Demer."

ERS and Envisat radar images were acquired for the rivers corresponding to 
historical floods that occurred in 1993, 1995, 1998 and 2003. Because radar 
imagery records surface roughness instead of reflected light, it is a good means 
of detecting flowing and standing water. High resolution IKONOS and Landsat-ETM 
optical imagery became the basis of risk maps; products valued by the insurance 
industry as well as water authorities.

"With risk mapping you are combining three different variables," explained 
Willems. "First is the spatial extent -- which areas will flood. Then comes the 
type of areas will be affected; a flooded meadow won't cause as much damage as 
an inundated urban area. The final variable is the return period -- will the 
flood recur once a year, every ten years or every 100 years?"

Combine them together and you can quantify how likely flood damage is for a 
given area, and be guided how much should reasonably be spent either to guard 
against it or insure against it. AWZ has already updated flood damage and flood 
risk maps in the two river basins based on the high-resolution imagery.

With historic flood mapping for simulation calibration, Envisat data was found 
to be more accurate than ERS. Envisat's Advanced Synthetic Aperture Radar (ASAR) 
instrument has several advantages over its predecessor, including beam steering 
capability for increased temporal coverage, a wide swath option and alternating 
polarisation modes -- all of which give it an edge in flood detection.

The FAME project is now formally concluded, although AWZ hopes to acquire 
Envisat and Radarsat data in tandem if further flooding occurs this winter, 
which would give an effective revisit time of one or two days. A decision has 
still to be made on extending the FAME service, which was funded by ESA's Data 
User Programme.

"Combined with other flood information sources, satellite data can definitely be 
effective," said Boey. "Flanders is not a big place, so a few satellite images 
have the potential to provide us with objective knowledge of the whole area.

"For us, a very useful part of the FAME project has been familiarising ourselves 
with the area of Earth Observation, and so making it much more likely we will 
make operational use of it in future."

Related articles

* Après le déluge: ERS and Envisat imagery contribute to European flood relief
  http://www.esa.int/esaCP/ESAZODZPD4D_index_0.html
* Satellite view aids Saône flood mapping
  http://www.esa.int/esaSA/ESAOAUUM5JC_earth_0.html

Related links

* Data User Programme (DUP)
  http://dup.esrin.esa.it/
* FAME
  http://www.sadl.kuleuven.ac.be/fame/project.htm

IMAGE CAPTION:

[Image 1:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html]
An unidentified man tries to stop the water with sandbags in Sint-Denijs 
Westrem, Belgium, as water floods parts of the community after days of 
torrential rains, Friday, Jan. 3, 2003.

Credits: AP Photo/Yves Logghe

[Image 2:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead2]
This diagram shows how model results compare with the reality of the flood on 
the river Demeter in January 1995. It is an overlay of an ERS SAR-derived flood 
map for 30 January 1995 (in yellow), with the existing Flemish map of peak 
floods for 1995 (in red) the MIKE 11 hydraulic flood simulation results for 30 
January 1995 (in brown) and the MIKE 11 hydraulic flood simulation results at 
the peak moment (in blue).

Credits: ESA

[Image 3:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead3]
Combining Earth Observation SAR data and flood simulation models to display 
likely flood return periods for a stretch of the river Dender. The area 
highlighted in green is likely to flood annually; the area in purple will most 
probably be revisited by floods within a decade, while the area in red is likely 
only to see floods once a century.

Credits: ESA

[Image 4:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead4]
The Flemish Water Authority AWZ updated their flood risk mapping using 
high-resolution IKONOS data acquired as part of the FAME project. Here part of 
the river Dender is shown, the flood risk mapped in Euro divided by square 
metres divided by year. Risk maps are useful to insurance companies as well as 
the water authorities and local government.

Credits: ESA

[Image 5:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead5]
This Envisat ASAR image acquired 0956 local time on 2 January 2003 of a flooded 
region shows the newer instrument's superior capability to detect flooded areas. 
Areas outlined in red or green are flooded. Compare its success rate to the 
ERS-2 SAR image taken at almost the same time (seen below).

Credits: ESA

[Image 6:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead6]
This ERS SAR image acquired on 2148 local time on 2 January 2003 is not as 
successful at identifying flooded areas (shown within red and green outlines) 
than a comparable Envisat ASAR image (see above).

Credits: ESA

[Image 7:
http://www.esa.int/export/esaCP/SEMLWHXLDMD_index_1.html#subhead7]
Envisat is in orbit at an altitude of 800 km -- much too far for any astronaut 
to ever come visiting. But to glimpse what Europe's environmental satellite 
looks like in space, the German Research Establishment for Applied Science FGAN 
has used its Tracking and Imaging Radar (TIRA). It consists of a 34-metre 
parabolic antenna system with a narrowband L-band tracking radar and wideband 
Ku-band imaging radar providing high target resolution. The TIRA system is also 
used to image meteoroids and space debris.

Credits: ESA