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Worksheet Introduction - Change Detection and Hazard Assessment
When monitoring changes in a volcano, we observe the dynamic processes and changes over time (multitemporal). This is enabled by satellites that fly in defined orbits and have the possibility of observing the same spot on Earth at regular intervals. The existence of large satellite archives also allow us to look at past observations (e.g. the Landsat programme exists since 1972, aerial images from even earlier).

Satellite sensors acquire information at different wavelengths of the electromagnetic spectrum (multispectral) and can therefore detect features which cannot be identified in the visible part of the spectrum. Satellite images also cover large areas which can be used to monitor large regions, or regions which cannot be observed from Earth (e.g. hostile terrain), or to get an overview of a region which cannot be observed from the ground. Moreover, less logistical effort is required, and satellite images can be an alternative to field survey.

All the above mentioned points play a key role in the following exercise, which also aims to extract information for hazard assessment. We will see how satellite data can be used for:

  • Analysing and inspecting a volcano
  • Monitoring changes of a volcano over time
  • Detecting lava in infrared bands
  • Assessing possible threats to humans by creating a hazard map
In this exercise we will use data from Landsat 7 and Landsat 5, GIS data, and terrestrial photos. The ETM+ (Enhanced Thematic Mapper) instrument onboard the Landsat 7 satellite is a multispectral sensor that acquires images in eight spectral bands, plus one panchromatic band. The spectral bands range from 0.45μm (visible) to 12.5μm (thermal infra-red), as summarised in the table. The Panchromatic band has a higher resolution due to the much broader spectral bandwidth. The Thematic Mapper (TM) instrument onboard Landsat 5 does not have a panchromatic channel.
Landsat 7 ETM+
Spectral Resolution (μm)BandSpatial Res. (m)
Band 1: 0.450 – 0.515Blue30
Band 2: 0.525 – 0.605Green30
Band 3: 0.630 – 0.690Red30
Band 4: 0.760 – 0.900Near IR30
Band 5: 1.550 – 1.750Mid IR30
Band 6: 10.40 – 12.5Thermal60
Band 7: 2.080 – 2.35Mid IR30
Band 8: 0.52 – 0.92Pan15
Landsat data
Download the file on the right.

Change Detection and Hazard Assessment
Exercise 1: Exploring the volcanoExercise 2 : Visual interpretation using terrestrial photographsExercise 3: Lava detection: crisis images and mapsExercise 4: Hazard assessment: GIS can help!
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