Our Spatial Planet

Displacement Map from TerraSAR-X

The largest disaster of 2010 so far continues to unfold. Aftershocks are hitting Haiti. Understanding the dynamics of the fault is crucial for planning evacuation and relief operations. TerraSAR-X can image the whole affected area independent of cloud conditions. Using correlation matching DLR extracted the east-west and north-south shifts. The results show upto 2.8m shift along the fault line.

The openlayers project and telascience have started putting together a web portal for the data flowing through from the disaster charter and other sources. EROS imagery shown in the previous post will be available soon.

Haiti UAV Imagery

20cm digital aerial imagery from IOJ as well as 50cm Intermap IFSAR digital surface model over Lake Victoria, NSW and integrated into NEXTIMAGE have been used to produce this video clip.

Lake Victoria, high resolution aerial imagery and terrain model. from apogeeimaging on Vimeo.

Apogee and Intermap have partnered to bring you the very best in imagery and digital terrain models in 2009 over Australia.

This fly-through has been made using very high resolution digital aerial imagery at 10cm resolution draped over an IFSAR digital terrain model with an exceptional accuracy of 50cm over the Murray Mouth and the Coorong in South Australia.

To display the following video in full screen High Definition (up to 1280×720), click the link below and righ click on the video and select full screen.

http://www.vimeo.com/3567706

The Murray-Mouth and the Coorong, South Australia in 3D from apogeeimaging on Vimeo.

According to the Scope for Improvement 2008 report from Blake Dawson, an Australian legal service and strategic business provider, released November 2008, 52% of majors infrastructure projects in 2008 were not adequately planned. A significant increase from the 42% recorded just 2 years earlier, in 2006. Even more worrying, the lack of proper scoping resulted in more than a quarter of 1$bilion+ projects having cost over-runs of more than $200 million! And we are not surprised…

In the first stage of any infrastructure project planning, surveying the terrain is one of the most important steps in order to have an accurate spatial representation of the area. The larger the project, the more critical accurate spatial data is and a significant percentage of planning time, budget and personnel should be allocated to data collection.  The Report lists three of the “Main Factors” leading to poor scoping as “Lack of experienced personnel”, “Insufficient time” and “Insufficient site information”.

This is where the appropriate use of geospatial data from aerial or satellite sensors could provide the required information. Unfortunately it is at this very important step that the biggest mistake is usually made. Because of lack of time and experienced personnel, the planning of many multi-million or even billion dollar projects are based on inadequate geospatial data in terms of resolution or accuracy, resulting in increased costs and budget over-runs. The problem maybe due to a lack of understanding or appreciation of the importance of geospatial data in providing a solid project foundation. As an example, a project may require 1m contours and in view of inadequate planning for the associated data cost, a decision is made by management to derive the contours from freely available SRTM data. Technically this is not a problem, however deriving such apparent high accuracy from the 15-20 metre vertical accuracy of SRTM at a 90m posting is not sensible. While this sounds far-fetched, this example is based on an actual project and similar extrapolation of data without due care as to the warranted level of precision is a common occurrence.

Remote sensing has been extensively used geology, mining exploration, oil, gas and pipeline planning. Recent introduction of new sensors and techniques to improve accuracy and efficiency are allowing planners to perfom virtual field trips to gather accurate information before arriving on site. From the first assessment of a project to the logistical operation, and on going monitoring, remote-sensing is an indispensable tool for all stages of any major mining project. Time and cost as well as risks can be greatly reduced through the use of Remote sensing technologies.

A range of sensors and resolutions are available for the mining industry and an accurate assessment of the most suitable data for a specific task should to be conducted to get the greatest benefit. The following list gives an overview of which data and sensors are currently used:

· Optical imagery for vegetation classification, environmental impact assessments, site rehabilitation, and operation monitoring:

o  ALOS PRISM and Spot which offer relatively large coverage with a resolution around 2.5m and very soon the Rapideye constellation with its daily coverage and 5m multispectral resolution.

o    High resolution satellites such as IKONOS, QuickBird, EROS-A/B which offer a narrow swath but 1-m and sub-metre resolution

o     Digital airborne imagery up to 5cm resolution

o    Airborne Hyper-spectral sensors with some systems collecting up to 220 bands.

Fast monitoring over a mining site

· All weather Radar data for mine subsidence, stock pile, pipeline monitoring and gold exploration:

o  TerraSAR-X, Radarsat-2, Cosmo-Skymed, for a resolution range from 100m up to 1m

o    Airborne IFSAR with sub-meter resolution (ORI from Intermap)

· Digital elevation model for planning, modelling and quantitative structural mapping:

o Spaceborne Radar interferometry data for centimetre-scale changes measurements.

o   Stereo imagery from Airborne sensors

o Stereo imagery from Spaceborne sensors such as ALOS PRISM, Spot, IKONOS, QuickBird, EROS-A/B

o   IFSAR DEM form airborne IFSAR systems such as Intermap, Fugro.

o   LiDAR

Advanced processing methodology also allows for the manipulation of basic data sets revealing features that may be of interest in geological interpretation such as the surface benath sand dunes.

ALOS PRISM DEM

Digital Elevation Model after dune removal process

All these data are usually integrated into modeling software, GIS systems and 3D-visualisation tools in addition to ground information and thus present invaluable decision level information.

This video clip shows 36cm resolution aerial imagery draped over an IFSAR 1m z absolute accuracy Digital elevation model over Murray River, South Australia. The clip has been made with Apogee’s NEXTIMAGE.

Please wait while the video loads

In today’s world where everyone is looking for ways of improving efficiencies, Digital Elevation Models have many applications including Mining exploration, flood modelling, city planning, river and aquifer mapping, vegetation(density, height) mapping and many others in area such as road, rail, pipeline planning.

So you may be asking “What exactly is a Digital Elevation Model?”
Well, a Digital Elevation Model is a way of digitally representing the elevation at a given geographic coordinate. For every point in the DEM there are 3 values; the normal X and Y values represent the coordinates, and the Z value represents the relative height. Using these three points, we can accurately plot terrain into a visual format that makes it easier to use, while retaining the underlying data and allowing the user to extract accurate height data. The images below show 3D render of a DEM over the Coorong and part of Hindmash Island in South Australia beside a satellite image of the same area.

Coorong 50cm Z accuracy IFSAR DEM

So “Are all Digital Elevation Models the same?”
The short answer is no. There are 2 forms of DEM, DTM and DSM. DSM stands for Digital Surface Model and includes the vegetation and building elevation with the ground elevation. DTM stands for Digital Terrain Model. In a DTM the vegetation and building data have been artificially removed from the DEM to provide an elevation model of the underlying terrain.

How Digital Elevation Models are acquired?
DEM can be generated using different techniques and sensors:

• Radar Interferometry (InSAR): a SAR instrument sends microwave radiation and then record the strength and time delay of the returning signal to produce images of the ground. Elevation information can be extracted from the time delay difference between 2 SAR images over the same area. The Shuttle Radar Topography Mission (SRTM) is the most famous example of a global Digital elevation model based on space borne InSAR.  InSAR DEM can also be produced using Aerial IFSAR radar imagery to achieve better resolution and accuracy than space borne sensors. Intermap technologies provides this kind of digital elevation model worldwide.

• Aerial and Satellite photogrammetry: Two or more images are used to extract the height of any pixels on image stereo pairs utilising acquisition parameters such as focal length, principal points, platform location etc. (example ALOS PRISM DEM, SPOT DEM, EROS DEM)

• Direct coordinate acquisition: It can be achieved with surveying techniques and GPS measurement where 3 dimensional object positions are accurately determined and associated with positions on the surface the earth.

• LiDAR: LiDAR is a remote sensing mapping technique which uses a laser scanner to measure the distance between the sensor and the surfaces. Mounted on an aircraft of helicopter, millions of x,y,z positions are acquired and form a surface map. Ground LiDAR are used to measure features along profiles.

What can DEMs be used for?
When it comes to DEMs the uses are unlimited. They are essential for things such as urban planning, construction of pipelines and other infrastructure, hydrological modelling from flood prevention to tsunami predictions – remotely sensed elevation maps are invaluable to accurately map the terrain over large areas where the same data using conventional surveying methods would be prohibitively expensive. Accurate DEMs are used in flood mapping, physical modelisation,  where accuracy of the terrain mapping determines the accuracy of the resulting flood map. DEMs also have applications for precision agriculture and many other scientific and commercial areas.

Flood level using Adelaide IFSAR DEM

Interesting Related Links:
NEXTMap USA