2
SCALE ISSUES IN MULTISENSOR
IMAGE FUSION
MANFRED EHLERS AND SASCHA KLONUS
2.1 SCALE IN REMOTE SENSING
Scale is a term that is used in many scientific applications and communities. Typical
well-known measurement scales are, for example, the Richter scale for the magnitude
of earthquakes and the Beaufort scale for wind speed. We speak of large-scale
operations if they involve large regions or many people. Cartographers use the term
scale for the description of the geometric relationship between a map and real-world
coordinates. In remote sensing, scale is usually associated with the latter meaning the
map scale for typical applications of remote sensors. To a large degree, scale is
dependent on the geometric resolution of the sensor which can be measured in ground
sampling distance (GSD). The GSD is usually the same or similar to the final pixel
size of the remote sensing data set. In addition to the GSD, scale is also associated with
the level and quality of information that can be extracted from remotely sensed data.
Especially with the launch of the first SPOT satellite with independent panchromatic
and multispectral sensors, it became evident that a combined analysis of the highresolution panchromatic sensor and the lower resolution multispectral images would
yield better results than any single image alone. Subsequently, most Earth observation
satellites, such as the SPOT and Landsat series, or the very high resolution (VHR)
sensors such as IKONOS, QuickBird, or GeoEye acquire image data in two different
modes, a low-resolution multispectral and a high-resolution panchromatic mode. The
GSD or scale ratio between the panchromatic and the multispectral image can vary
between 1 : 2 and 1 : 8 with 1 : 4 the most common value. This ratio can even become
smaller when data from different sensors are used, which is, for example, necessary if
13
Scale Issues in Remote Sensing, First Edition. Edited by Qihao Weng.
2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.
SCALE ISSUES IN MULTISENSOR
IMAGE FUSION
MANFRED EHLERS AND SASCHA KLONUS
2.1 SCALE IN REMOTE SENSING
Scale is a term that is used in many scientific applications and communities. Typical
well-known measurement scales are, for example, the Richter scale for the magnitude
of earthquakes and the Beaufort scale for wind speed. We speak of large-scale
operations if they involve large regions or many people. Cartographers use the term
scale for the description of the geometric relationship between a map and real-world
coordinates. In remote sensing, scale is usually associated with the latter meaning the
map scale for typical applications of remote sensors. To a large degree, scale is
dependent on the geometric resolution of the sensor which can be measured in ground
sampling distance (GSD). The GSD is usually the same or similar to the final pixel
size of the remote sensing data set. In addition to the GSD, scale is also associated with
the level and quality of information that can be extracted from remotely sensed data.
Especially with the launch of the first SPOT satellite with independent panchromatic
and multispectral sensors, it became evident that a combined analysis of the highresolution panchromatic sensor and the lower resolution multispectral images would
yield better results than any single image alone. Subsequently, most Earth observation
satellites, such as the SPOT and Landsat series, or the very high resolution (VHR)
sensors such as IKONOS, QuickBird, or GeoEye acquire image data in two different
modes, a low-resolution multispectral and a high-resolution panchromatic mode. The
GSD or scale ratio between the panchromatic and the multispectral image can vary
between 1 : 2 and 1 : 8 with 1 : 4 the most common value. This ratio can even become
smaller when data from different sensors are used, which is, for example, necessary if
13
Scale Issues in Remote Sensing, First Edition. Edited by Qihao Weng.
2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.