Global geospatial data from Earth observation: status and issues

ABSTRACT

Data covering the whole of the surface of the Earth in a homogeneous and reliable manner has been accumulating over many years. This type of data became available from meteorological satellites from the 1960s and from Earth-observing satellites at a small scale from the early 1970s but has gradually accumulated at larger scales up to the present day when we now have data covering many environmental themes at large scales. These data have been used to generate information which is presented in the form of global data sets. This paper will give a brief introduction to the development of Earth observation and to the organisations and sensors which collect data and produce global geospatial data sets. Means of accessing global data sets will set out the types of data available that will be covered. Digital elevation models are discussed in a separate section because of their importance in georeferencing image data as well as their application to analysis of thematic data. The paper will also examine issues of availability, accuracy, validation and reliability and will look at future challenges.     

A WORKING METHOD FOR THE CALIBRATION OF PLOTTING INSTRUMENTS USING COMPUTERS

Methods of testing and adjusting photogrammetric plotting instruments are reviewed and the precision of traditional simple methods is investigated. Practical tests confirm the theoretical results and suggest the most efficient methods for determining the co-ordinates of the perspective centre, the principal distance and the adjustments necessary to the interior orientation. These methods are incorporated in a procedure for testing instruments using either a large computer or a desk top computer. It is concluded that an improvement in accuracy and efficiency can be obtained by using redundant observations and a computer to handle the mathematical adjustment.     

IMAGES FROM SPACE: THE FUTURE FOR SATELLITE PHOTOGRAMMETRY

The requirements for 1:50 000 scale mapping are reviewed and the potential of satellite data for topographic mapping is considered in that context. Ground control and alternatives in the form of sensors on the satellite are discussed. The application of data from photographic and push broom sensors is considered in terms of information content, geometry and available plotting equipment. The paper concludes with a brief consideration of the possibility of using digital compilation.     

Comparison of two physical sensor models for satellite images: Position–Rotation model and Orbit–Attitude model

The main objective of this paper is to compare two types of physical sensor models of linear pushbroom satellite images: one that uses position and rotation angles as model parameters and one that uses orbit and attitude angles as model parameters. Comparison is carried out by two accuracy measures: the accuracy of bundle adjustments and the accuracy of estimating exterior orientation parameters. The first measure has been used widely to indicate the mapping accuracy of sensor models. It is argued that the second measure is also important for certain applications. The two types were implemented with different sets of unknown parameters and tested with two KOMPSAT-1 Earth Observing Camera (EOC) scenes and GPS-derived control points. In terms of the first measure the two models produced similar results whereas in terms of the second measure the one based on orbit and attitude outperformed the other. It seems better to use this model if one wishes to retrieve satellite orbit or attitude through bundle adjustments.