It has taken a long time, but it
appears we are successfully generating a high quality three dimensional map of
the Earth’s surface. Integrating that
image with other types of satellite data will be extremely valuable. A lot of that goes on all the time in
resource management programs and this will bring it all a a huge step and make
it efficient.
Sooner or later we will have a
high resolution globe that will integrate with google maps and be many times
clearer and more accurate.
Recent events have reminded us
that sub surface rocks need to also be mapped in the shipping lanes. A simple outlier can sit and wait forever and
knowing it is there prevents surprises.
A step closer to mapping the Earth in 3D
by Staff Writers
A year after the initial operational phase, TanDEM-X has mapped all
land surfaces on earth except Antarctica
completely. Elevation models have been generated with the data. According to
the color scale, green tinted areas already comply with a the requirement of a
two-metre accuracy. Yellow-coloured areas must be recorded a second time,
reddish surfaces also require recording from a different angle. Gray-shaded
strips have been recorded, but have yet to be processed. Full size image here
After a year in service, the German Earth observation satellite
TanDEM-X, together with its twin satellite, TerraSAR-X, have completely mapped
the entire land surface
of Earth for the first time. The data is being used to create the world's first
single-source, high-precision, 3D digital elevation model of Earth. The German Aerospace
Center
It is reminiscent of ballet on ice; throughout the last year, Germany
"The mission is running better than expected and there have been
no unscheduled interruptions in the programmed formation flight of the two
satellites. All safety mechanisms are functioning robustly and in a stable
manner," enthuses Manfred Zink, project manager
for the TanDEM-X ground segment at DLR. Over the course of 2011, the distance
between the satellites was progressively reduced down to the minimum permitted
value of 150 metres.
'Radar eyes' working with millimetric accuracy
This satellite mission is the first of its kind; it remains unique and is highly complex, even for experienced engineers. "Following the launch of TanDEM-X on 21 June 2010, there was a six-month test phase, during which we subjected the satellite and its behaviour in near-Earth orbit to intense scrutiny and carried out our calibration work," Zink recalls.
During this time, TanDEM-X commenced formation flying with its identical
partner satellite, TerraSAR-X, which was launched in 2007. On 14 December 2010,
the operational part of its mission began, collecting data for the
high-precision elevation model.
The radar system views the ground from two different points in space, achieving
'depth perception' in a manner similar to binocular vision in humans. "The
generation of accurate elevation data calls for precise coordination of data
from and between both satellites," explains Gerhard Krieger, systems
engineer for the TanDEM-X mission.
Differences, for example in the cable lengths on the two radar instruments,
as well as the distance between the two satellites, need to be calibrated very
precisely. "This is a truly enormous challenge when you consider that a
millimetre of variation can cause up to one metre of elevation error,"
says Krieger.
The strips of terrain recorded by the satellites are processed into
elevation models measuring 50 by 30 kilometres. Due to the ultra-precise
calibration, when this 'basic data' is compiled at the end of the process to
generate a global 3D map, it is already of very high quality.
By mid-2013, TanDEM-X and TerraSAR-X will have imaged the complete land
surface area of Earth - roughly 150 million square kilometres - several times. The
intention is to create an exceptionally accurate, global and homogeneous 3D
elevation model that promises to be of equal interest for commercial and
scientific purposes.
Data quality depends on ground reflectance
Initially, at least two complete coverage cycles of Earth's land surface were planned. Some parts, one example being the vast majority of
"The level of precision depends on how well the ground reflects
the radar pulses transmitted - and subsequently received - by the
satellites," states Manfred Zink. For example, the Sahara
is more difficult to image because the signal literally 'sinks into the sand'
and is lost. For regions of dense vegetation, such as rain forests, additional
imagery and careful adjustment of the distance between the satellites are
necessary.
"We are going to be left with a few blank areas on the map, but we
do of course seek to minimise these gaps," states Zink as he thinks about
the coming months.
Better understanding Earth as a system
"We want to gain a better understanding of Earth as a system and to employ the data for climate and traffic research, for example," says Irena Hajnsek, scientific coordinator for the TanDEM-X mission. In 2011, she gave the 'green light' for 166 of the research applications submitted to DLR. "Most of these originated in the
The TanDEM-X capabilities are to be used to address questions of land
usage and vegetation, hydrology, geology and glaciology," explains
Hajnsek. The two Earth observation satellites can also generate information
about the height of the snowline or the change in ice masses of the two polar
regions, as well as provide geological maps of regions subject to volcanic
and/or earthquake activity. The speed of ships or road vehicles can be
measured, as can changes in the natural world.
The work performed by these two radar satellites is also valuable for agriculture.
"Based on the height and structure of a plant - such as rapeseed, for
example - it is possible to draw conclusions about its quality and
biomass," states Hajnsek.
No comments:
Post a Comment