This article demonstrates the value of geo-monitoring using examples of imagery provided by the Airbus Defence & Space constellation of radar and optical earth observation satellites.
Addressing basic principles for prosperity such as education, leadership, political stability, health, population growth management, infrastructure, management of resources, industrialisation of products, and attracting investment, are all stepping stones to establish a sustainable economy for any country. Suitable land administration is a key principle for assessing and monitoring progress within any country. It is a foundation block to measure progress.
When spatial information is analysed in a time series method, the evidence of the status quo on the ground becomes factual. Satellites such as SPOT 6, Pléiades, TerraSAR-X and Deimos-1 play a key role particularly for application areas such as agriculture, mining, and infrastructure. The earth observation satellite constellation operated by Airbus Defence & Space offers a wide range of temporal, spatial and spectral diversity to address various geo-information requirements.
Fig. 1: Slope stability measurement usingTerraSAR-X.
Optical assets
SPOT 6 and SPOT 7
The SPOT systems can provide target specific information to detect and identify objects larger than 4,5 m. The system has the capability to take 60 km wide strips up to 1000 km in length, or to cover areas such as 300 x 330 km in one satellite pass. The SPOT 7 satellite was launched on 30 June 2014 and is expected to become operational in October 2014. These satellites are an excellent resource to establish national baseline information for topographical maps and resource management. The orbital path of the satellites enables a nadir revisit of every 26 days, yet it is also capable of doing an off-nadir acquisition that exceeds 30°. The latter enables a two to three day revisit per target opportunity and can be reduced down to a one day revisit capacity using wider acquisition angles.
In addition, SPOT 6 and SPOT 7 agility allows for targeting of any point within a 1500 km-wide across track corridor (45° viewing angle). This also opens the way to various acquisition scenarios matching different applications, e.g. the strip mapping mode to collect wide areas in a single pass. While the nominal acquisition scheme for the SPOT 6 and SPOT 7 satellites is north to south, they may also be tasked to follow linear targets such as communication lines, rivers or coastlines. The SPOT 6 and SPOT 7 systems also incorporate native tasking modes for stereo or tri-stereo acquisition, for accurate 3D extraction purposes.
Pansharpened and orthorectified images are standard. The orthorectification process relies on Airbus Defence and Space’s elevation layer (Elevation30, available for over 75 Mio km2 worldwide). The registration of SPOT 6 and SPOT 7 images on Elevation30 enables a perfect overlay for applications implying multi-source or multi-date data in a GIS environment, facilitating change detection processing, map revision, or complex projects.
To summarise its strengths, SPOT 6 and SPOT 7 maintain key characteristics (both in terms of satellite performances and service) which guarantee the continuity of a High Resolution (HR) offer fitted for medium scale cartographic projects.
Pléiades 1A and 1B
The Pléiades system provides very high resolution imagery products. The product includes a processed 0,5 m panchromatic and 2 m four band multispectral image product. The highly agile system can target up to 20 targets within a 1000 x 1000 km block with a 20 x 20 km scene swath. This is said to be the ideal system to collect very high resolution images over a specific target. The system provides for an intra-day revisit over a specific target (persistent tasking) or excellent periodic monitoring (up to daily). The identification of objects greater than 1,5 m is achievable with this system complimented by its 12 bit spectral data (4096 values), enabling the distinguishing of objects in the darkness of shadow more easily. It is an accurate, reactive and available system.
Fig. 2: SPOT 6 satellite image, (A) natural colour composite, false colour composite and (C) NDVI indices over agricultural fields.
DEIMOS-1
Medium resolution satellites refer to a wide swath system with moderate spatial resolution of 20 m+ ground sampling distribution (GSD). These systems can acquire a scene size of up to 900 000 km2 as a single collection with a high revisit frequency rate. These systems are ideal for monitoring large areas e.g. the monitoring of seasonal agricultural crops.
Radar assets
TerraSAR-X and TanDEM-X
These Synthetic Aperture Radar (SAR) satellite systems feature world leading X-band radar technology with an excellent accuracy. The satellite features several acquisition modes and can provide 0,25 m to 40 m spatial resolution data. The higher the resolution, the smaller the swath.
The Wide Scan SARmode (270 x 200 km @ 40 m GSD) is particularly suited for maritime applications, as well as the ScanSAR mode (100 x 150 km @18,5 m GSD), which can offer large area specific ship detection. The StripMap and SpotLight modes are excellent for high precision monitoring and can even document surface movements in millimetric accuracy. Time Series Interferometric Analysis (including techniques such as Persistent Scatter Interferometry and Small Baselines Subset) is applied to derive the movement measurement over the area of interest (see Fig. 1).
With its 25 cm resolution, the TerraSAR-X Staring SpotLight mode is said to provide the highest resolution SAR imagery commercially available today. This very-high resolution imagery is suited for the precise detection, recognition and identification of objects.
PAZ
The PAZ satellite (owned and operated by Hisdesat) will be the 3rd SAR satellite available within the Airbus Defence and Space constellation. It is almost a replica of the TerraSAR-X and TandDEM-X satellite series. The launching schedule for PAZ is set for early 2015. This additional system will increase the monitoring frequency: global mean revisit time is predicted to at least increase from 56 h today to ~28 h in 2014. This increase in data availability is ideal for maritime monitoring. PAZ’s true innovation is the AIS (Automatic Identification System) receiver on board the satellite, which enables the reception of AIS signals at the same time as the SAR image acquisition – a leap forward for the maritime surveillance ability from satellites.
Fig. 3: Open surface mine examples (A) Péiades (B) SPOT 6.
Elevation models
Additional technology offered by the company includes its diverse GEO Elevation offerings, which rely on its satellite constellation to offer high quality digital surface models (DSM) and digital terrain models (DTM). From off the shelf elevation models such as Elevation30 to tri-stereo/stereo collections for creating DSM/DTM over any area in the world.
Geo-applications for land administration
Land administration not only refers to a system to manage cadastre or its integration to a property taxation solution. Land administration, in this article, refers to the efficient and effective management and control over a country’s resources. The ability to identify suitable land capability for commercial agriculture as well as the managing of the fine balance between environmental protection and mining activities are some examples.
Mining investment into Africa during 2012 by foreign investors was estimated at US$50-billion, creating more than 106 000 sustainable job opportunities. The challenge is to manage these resources effectively and to ensure good governance to fight corruption as the rational for the establishment of the “Extractive Industries Transparency Initiative (EITI)”.
Agriculture
The African continent is blessed with high agricultural potential in terms of land availability, soil and water, particularly in the central regions of Africa. The demand for food and food security solutions at country, regional and global levels is growing. If Africa can manage to commercialise its agricultural potential fully, it could become one for the largest producers for a rich variety of food products. Fundamental pillars to achieve the latter are education, infrastructure, establishment funding and political stability. The contribution of remote sensing to agriculture is its ability to assist with spatial planning, land suitability indices, crop yield calculations, monitoring and precision farming. Applying a multi-sensor approach to analysis from macro (national) to micro level (small field) provides for a rich platform for spatial information for agronomic applications (see Fig. 2).
Mining
The geological diversity on the Africa continent provides for rich mineral fields that include gold, diamonds, coal, copper, platinum, titanium, and so on. The existence of many oil and gas fields further increases the interest of developed nations in the African continent.
Mine exploration activities are distributed all over the African continent. Open surface mines, in particular, have resulted in long term devastation to the environment. Years of sub-surface mining, such as deep gold mines, have created acid water which, when it surfaces, becomes a serious environmental threat, for example on the East Rand region of Johannesburg. It is critically important therefore to balance the economic value of mining versus the impact it has on the environment. This can be achieved through good spatial monitoring and management principles.
Fig. 4: (A) (B) (C) (D)Pléiades time series analysis over a construction site, Arena Corinthians Soccer Stadium, Brazil.
The TerraSAR-X satellite is the ideal technology to monitor any change in slope stability (subsidence, stability and uplift) (see Fig. 1). Various mines make use of “tailing dams”, which contain highly polluted mine water. If a tailing dam breaks or the water filters through to non-toxic ground water tables or natural rivers, disaster is imminent. Optical satellites such as SPOT 6 and Pléiades are ideal for monitoring any contamination in the surrounding vegetation around mine activities (see Fig. 3). The NDVI indice is a well-known remote sensing algorithm that can monitor vegetation health over a period of time, especially when using the near-infrared (NIR) multispectral band of the satellite.
Infrastructure
Large capital investments in infrastructure such as roads, power plants, bridges, industrial and housing developments require extensive management and control. Continuous monitoring of projects during the project lifecycle is critical to ensure that these projects are on schedule and that payments are done according to measurable achievements. The constellation of satellites offered by Airbus Defence and Space provides exactly this service. The frequent monitoring and reporting on any changes that occur during a project provides for factual spatial information. Spatial information contributes to the visual interpretation of an area, the measurement of physical changes, area measurement, linear measurements, and so on (see Fig. 4).
Land administration
Land administration in the sense of managing cadastre, deeds and property information is a domain that also needs to be highlighted. A country that manages and controls its property information correctly can ensure consistent property tax income and good governance.
The Land Administration, Valuation and Information Management System (LAVIMS) project was an initiative by the Government of Mauritius designed to modernise land administration by greatly improving access to information between different departments and creating a complete and up-to-date national valuation roll. Implemented by Airbus Defence and Space, LAVIMS is really four sub-projects in one, including: development of the cadastre; implementation of a digital deeds management system; valuation of properties; and information management. At the highest and strategic level, it is the objective of the authorities to establish a beneficial LAVIMS that will lead to improved urban planning and infrastructure development, enhanced environmental management, and improved production of national statistical data.
Conclusion
Satellite observation systems can contribute to change detection, identify structures or measure surface substance changes during a frequent monitoring schedule. The constellation of satellites available from Airbus can collect geospatial information over very large geographical areas or specific targets. The availability of optical as well as radar satellites enables the collection of information even in challenging weather conditions. The orbital positions of the constellation of satellites allow for various monitoring options. Applying this earth observation technology effectively can contribute to the management of various land administration activities in Africa. It is a technology that can objectively and factually provide information for the public and private sector to monitor progress, improve resource management and ensure sustainable implementation of socio-economic projects.
Acknowledgement
This paper was presented at AfricaGEO 2014 and is republished here with permission.
Reference
[1] Airbus Defence and Space 2014, Airbus Defence andSpace, Geo-Intelligence, Toulouse, France, viewed 20 March 2014, www.astrium-geo.com/en/176-mauritius-case-study.
[2] BDFM Publishers2013: BDLive, Johannesburg, South Africa, viewed 3 March 2014, www.bdlive.co.za/national/science/2014/03/14/acid-mine-drainage-project-opens-on-east-rand.
[3] E Tempelhoff: Satelliet soek minerale bronne in Afrika. Beeld, 13 February 2014. Wikimedia Foundation 2001, Wikipedia, viewed 11 March 2014, <http://en.wikipedia.org/wiki/Normalized_Difference_Vegetation_Index>.
Contact Corné Eloff, Airbus Defence & Space, Tel 012 686-8904, corne.eloff@eads.co.za
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