Monitoring land use, forestry and agriculture

Context

Illustration: Forest clearing using fires

Globally, forest resources now attract unprecedented attention. The concern extends both to their value and to the environmental effects of their destruction. There are approximately 3400 million ha of forest globally, representing nearly 25% of the world's land area. Pressures on forests to provide economic resources are increasing rapidly. The rate of tropical forest destruction is not known with any accuracy, but is estimated by the Food and Agriculture Organisation (FAO) of the United Nations as around 15.4 million ha per year. Their destruction has many serious long term environmental implications.

Security of food supply is a concern throughout the world. Public and private-sector organisations from local to global scales have been established to monitor food supply, with a responsibility to forecast local harvests and assess import or export requirements to control prices and meet the needs of the population. The European Union, for example, not only has a requirement to collect statistics on crop yield and production, but also to monitor the implementation of the Common Agricultural Policy. Large scale monitoring of agricultural land is costly with ground-based methods, and as a consequence there have been applications in agriculture for optical satellite data some years. Additionally, land monitoring can be cost-effective and efficient using radar data especially in areas covered by clouds for much of the year.

Contents

Monitoring of land cover is discussed here:

• Agricultural monitoring
• Tropical forest monitoring

A more general precis of the applications of ERS relevant to cartographic applications, whether simply deriving the topography (Digital Elevation Modelling) or on a thematic 'land-use' basis are covered in Cartography and Topography

The contribution of data from the ERS series

Illustration: A multitemporal SAR image from ERS-1

In the original mission objectives, observing the land surface was viewed as an experimental application for ERS-1 data. However, the ability to monitor crop development and forestry changes independent of weather conditions, offers a major potential application area for ERS data.

An important technique which has been developed for terrestrial applications is multitemporal SAR analysis. Three input SAR datasets, acquired at different times, are assigned the colours red, green or blue. Changes between acquisitions can then be detected by observing the colours that appear in the imag which reflect the change in the state of land cover. Crops planted at varying times and developing at varying rates can be identified, increasing the accuracy with which crop areas can be mapped and acreage estimated. Multitemporal analysis is also being applied to monitor logging in forested areas.

The ability to choose the time of observation is also important in agricultural applications, and particularly for deriving suitable information to support crop yield prediction. The microwave capability offered by the ERS series means that observation is not limited by weather or light conditions as are optical data.

Agricultural monitoring

Illustration: Rice terraces

Monitoring of the Common Agricultural Policy of the European Union, in particular the implementation of the so-called 'set-aside' agreement in which farmers are paid subsidies to limit their production, is now undertaken partly with Earth Observation data. Earth Observation data also provides a common data source and standardised methodology for the collection of agricultural statistics. The use of ERS SAR data is gradually being introduced as part of this effort. Monitoring the scale of global crop production and trade has been identified as an area in which ERS SAR data may be able to assist. In particular in South East Asia, several governments are now looking into the use of ERS data for monitoring their rice crops.

Tropical forest monitoring

Illustration: Forest clearing in the tropics

The requirements for information on the world's forests are varied. Some established mapping and monitoring systems are introducing ERS SAR data, and other organisations are starting projects as a result of having access to this new source of data. ERS provides information for maps of forest extent and type in tropical areas which have not previously been mapped due to almost continuous cloud cover.

SAR data are being used as the unique data source, and in conjunction with other remotely sensed data, to map forest damage, the encroachment of agriculture onto forested areas unsuitable for development, and in general to provide inventories of timber areas.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry