Home' Position : Position Apl May 2015 Contents The disastrous floods that have
ravaged several parts of Australia
during the past decades could have
been more accurately predicted, and the
damage they caused lessened, with the
latest tools now available, using GPS and
data from various other satellites, together
with the more traditional measurement of
parameters on the ground.
A complex phenomenon, flooding is
a consequence of many factors, includ-
ing the amount of water vapour in the
atmosphere, the water level in lakes and
reservoirs, soil moisture, the level of salin-
ity in the oceans, and land topography.
Following the floods in Queensland in
2011, Geoscience Australia initiated the
Natural Disaster Insurance Review, which
aimed, among other things, to improve
the consistency across the country in the
way flood risk information is collected
and made available. Geoscience Australia
also established the National Flood
Risk Information Project that started in
July 2012 with funding for four years.
The project aims to improve the quality
and accessibility of flood information.
The project will publish the Australian
Rainfall and Run-off Guidelines, and will
analyse Australia's archive of satellite
imagery to derive water observations to
help understand flood events.
To cater for certain insurance policies,
Geoscience Australia introduced a
standard definition of flood. The definition
applies when an insurer offers flood cover
for a home building, home contents, small
business or strata title insurance policy.
For this purpose, a flood is defined as:
"The covering of normally dry land by
water that has escaped or been released
from the normal confines of any lake, or
any river, creek or other natural water-
course, whether or not altered or modified,
or of any reservoir, canal, or dam."
One of the main determining factors in
any flooding event is the amount of water
vapour in the atmosphere, particularly
in the form of 'atmospheric rivers'. These
are relatively narrow corridors in the
atmosphere in which large amounts of
water vapour are transported horizontally.
Atmospheric rivers are typically several
thousand kilometres long and a few
hundred kilometres wide. A single
atmospheric river can carry a greater
volume of water than the Amazon
River. There are three to five of these
atmospheric rivers within a hemisphere at
any given time. They are the major cause
of extreme precipitation events that cause
flooding in mid-latitude, westerly coastal
regions of the world.
Using GPS to
GPS signals can be used to measure
the amount of water vapour in the
atmosphere. The time it takes for a GPS
signal to travel from a GPS satellite to a
GPS receiver on the ground is modified
by the amount of water vapour in the
atmosphere. The signals are delayed by
the water vapour in the atmosphere and
that delay is a measure of the amount
of water vapour. Together with a surface
pressure and temperature measurement,
that delay can provide a fairly good
estimate of the amount of water vapour
that could lead to precipitation, and allow
predicting rainfall and flash floods. By
using existing and continuously operating
reference stations (CORS) as fixed points
on the ground, it is possible to obtain
information on thunderstorms, flash
flooding and seasonal monsoon events.
There are several such GPS ground-
based atmospheric sounding systems
worldwide, including the NOAA (National
Oceanic and Atmospheric Administration)
GPS-IPW (IPW=integrated precipitable
water) project in the US, the GPS Earth
Observing Network (GEONET) in Japan,
the Australian Regional GPS Network
(ARGN), the Royal Observatory of Bel-
gium, the Integration of RGP and REGAL
Network of France, Goteborg GPS Net-
work of Sweden, and the GPS Atmospheric
Sounding Project (GASP) of Germany.
ARGN consists of a network of
permanent geodetic quality GNSS
receivers on geologically stable marks
in Australia. These sites provide data on
crustal dynamics and sea levels. Data
from the ARGN network also contributes
to the International GNSS Service.
Geoscience Australia also operates
Water Observation from Space (WOfS)
-- a web service displaying surface water
observations obtained from satellite
imagery for all of Australia from 1987 to
the present day.
One of the largest GPS networks in
the world, originally installed to measure
tectonic movements and to monitor and
predict events such as earthquakes and
flash floods, is in southern California.
A team from the Scripps Institution of
Oceanography in San Diego, California,
NASA's Jet Propulsion Laboratory in Los
Angeles, and NOAA have joined forces
to take advantage of that network to also
observe the amount of water vapour in
the atmosphere. The network includes
nearly 500 GPS stations, and sensors such
as barometers and thermometers.
Predicting floods with GPS
Satellite view of flooding in southern and central Queensland, late December 2010.
Photo courtesy of Geoscience Australia.
24 position April/May 2015
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