The monitoring of land cover changes from remotely sensed aerial or satellite observations, used in conjunction with ground based observations, forms the basis of many operational monitoring systems used in regional natural resource management (NRM) programs. Consistent and comparable observations are fundamental to monitoring, though ideal data are often challenging to acquire when considering large spatial extents over extended time periods. During the course of such acquisitions, some (non-land cover related) parameters associated with the observations may have changed, which from a spatial and temporal perspective, must be taken into account if one wishes to compare land cover observations over large geographic areas revisited at regular intervals. Parameters that change may include: the relative position between ground, sensor, and sun; atmospheric conditions, which vary with wavelength; and the sensor response. This talk presents examples drawn from operational monitoring systems which the authors have developed over the passed 2 decades, and some of the issues and solution strategies adopted. These include methods for normalisation for geometric, radiometric and viewing geometry effects in images, as well as methodologies adopted for the interpretation of “similar” sensors.
Keywords: Monitoring; Remote sensing