Updated December 1998
by T. Negre, G. Grepin
56 pp, 30 figures, 6 tables
RSC Series No. 73, FAO, Rome 1997
Light Aerial Remote Sensing (LARS) systems are useful instruments for technicians and planners involved in local rural development. Still less well-known and widespread than photogrammetric or satellite-based techniques, LARS systems are however developing fast and do respond to specific requirements for local rural development operations.
The more common LARS systems are reviewed in this publication. They consist in photographic or video cameras operated from light planes and helicopters, hot air balloons, microlight airplanes, unmanned airplanes, kites and captive balloons or telescopic masts. The great variety of vectors offers various capabilities and possible applications.
Major applications were identified through a user requirement survey carried out with the FAO/Investment Centre and the International Fund for Agricultural Development (IFAD). They are listed hereafter and described in the first section of the publication.
Other important applications related to agriculture and food security are:
The publication also provides guidelines for the selection of the proper technical solution for meeting user requirements. Selection of the more adequate remote sensing system requires a detailed technical analysis. When compared to high resolution satellite techniques, LARS systems are to be preferred when finer resolution is required (under 2 m) or when the area of interest is reduced (roughly under 1,000 km2).
Among the various light aerial systems, light planes and microlights are the most adapted for operations covering several hundred to several thousand square kilometres (most applications), while the other systems are geared towards smaller-scale operations.
Captive systems such as kite and balloons are adapted to 1 to 50 km2 surveys, at village level or for small-scale agricultural or fishery schemes identification or planning. Mobile mast systems are low height devices mounted on vehicle. They are adapted to transect observation for rangeland, crops, young forest plantations and control for roads, dams, power lines, etc.
Other systems such as helicopters, hot air balloons and unmanned planes are still costly and may be recommended only for very specialised applications, requiring capabilities such as vertical take-off and still-motion flight (helicopters), very low height and silent flight (balloons) or absence of pilot for security reasons (unmanned airplanes).
Other important constraints and operational aspects to take into account are the local availability of vector and technician/pilot, flying and photographing authorisations, climatic conditions, operation timeframe.
Processing the photographs/videos recorded by the LARS system is another important and delicate step. There are two possible ways: analogue or digital. Analogue (film and paper-based) processing and analysis is recommended for projects where the computer component is small and no geographical database/Geographic Information System (GIS) is available. Analogue processing is relatively easy to learn for non-specialists and requires only basic processing equipment. Digital processing is to be preferred when the photographic/video information is to be included in a geographical database or GIS in order to be archived and digitally analysed.
Satellite positioning systems, such as the US Global Positioning System (GPS), are not properly LARS systems, but are covered in this document as they are complementary to LARS systems and increasingly used by agricultural development projects. Positioning systems give the exact geographical position of the observer at the moment of the measurement. They can be installed on-board boats and planes or hand-carried by ground teams. It is possible to directly couple positioning system and camera through a portable computer in order to automatically record the geographical location of the photograph. The navigation GPS offers a 100 m measurement accuracy in its basic configuration. Cost of more precise systems, such as Differential GPS or coupled GLONASS/GPS systems (up to 10 meters precision), should decrease in the coming months/years.
In order to provide more technical information to potential LARS users, the second part of the publication gives technical summaries of main LARS in which main technical and operational characteristics of these tools are reviewed with appropriate illustrations.
In the last part of the report, three case studies are proposed. They intend toshow practical results obtained with light aerial remote sensing for several applications in developing countries.
For a copy of the above publication, contact:
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00100 Rome, Italy