Remote Sensing Techniques Applied to Landslide Studies

by Eileen M. Brennan
 



 

Table of Contents

Introduction
Stage One:  Detection and Classification of Landslides
Stage Two: Monitoring Landslide Movement
Stage Three:  Analysis and Prediction of Slope Failures
Conclusions
Landslide Links
Bibliography

Introduction


Landslide studies can be organized into three phases

1) detection and classification of landslides
2) monitoring activity of existing landslides
3) analysis and prediction of slope failures in space (spatial distribution) and time (temporal distribution).

Remote sensing techniques can be and are often used in all three stages of a landslide investigation.
 
 

Examples of some remote sensing tools (not all of these will be discussed in this page):
 

Stage One:  Detection and Classification of Landslides


In order to study a landslide, you need to be able to view the size and contrast of the landslide features and the morphological expression of the topography within and around the landslide.  Parameters you might be interested in determining are the type of movement that has occurred, the degree of present activity of the landslide, and the depth to which movement has occurred.

The most common remote sensing tools used for the detection and classification of landslides are aerial photographs.  Aerial photography has become a standard tool aiding in the study of landslides.

Other types of remote sensing techniques used in the detection and classification:

Stage Two: Monitoring Landslide Movement
The second stage in a landslide study is typically monitoring the movement of a landslide.  This involves the comparison of landslide conditions over time, including the aerial extent of the landslide, the speed of movement, and the change in the surface topography.  There are several remote sensing techniques that are commonly used in this stage of a landslide investigation.
 

Remote sensing techniques:


Global Positioning System (GPS)
GPS is a useful tool for detecting first stage disaster and further mitigation.  It can detect movement of cm/yr, and aid in determining the boundary of the landslide area.  Monitors can be placed anywhere you can access, and they are relatively easy to operate.  There are some significant disadvantages involved in using GPS, however.  Several of these disadvantages are precision is affected by the number of observable satellites present, the obstruction of the observation point, and the monitoring of installed GPS receivers which have been placed out in the field.

Example:
Click here for an example of using GPS to monitor unstable slopes along I-70 in Colorado
 
 

Satellite imagery/RADAR imagery
There are many types of visible band satellite imagery that can help detect where slides have occurred or where they are about to occur.  Change detection images can be taken before and after movement occurred.  From these images you can often see surface disruption.  Radiometric and geometric calibration is required of the before and after images to make images that have changed stand out from those that have not.
 

Stereophotogrammetry
In the method of stereophotogrammetry,  a satellite acquires two images of the same ground scene within a relatively short period of time, so that it can view surface features have not significantly changed.  These images can be processed to get topography from the stereo pair of images. The series of stereo pairs offers a 3 dimensional evolution of the landslide over time.
 

Another example…
Click here for an example of using photogrammetry on the Slumgullion Landslide in Hinsdale County, Colorado
 
 

Stage 3:  Analysis and Prediction of Slope Failures


This image is one example of why it is so important to try to predict landslide occurrences and slope failures.  This is a picture of a debris flow from Rudd Canyon into Farmington, Utah, in Spring of 1983. (Photo: S. Ellen, USGS).
 
 


Debris flow hazard map of  a portion of the San Francisco Bay Region
 Click on the map for a larger image.





Landslide hazard analysis

Hazard – The probability of occurrence of a potential phenomenon within a specified period of time and within a given area (Varnes, 1984).

Zonation – The division of land into homogeneous areas or domains and their ranking according to degrees of actual/potential hazard caused by mass movements (Varnes, 1984).

Landslide hazard is typically depicted on maps which show spatial distribution of hazard classes, or “landslide hazard zonations.”  The development of these zonations requires knowledge of the processes active in the area being analyzed, and factors (geologic and triggering) leading to the occurrence of landslides.

Landslide hazard map of the Conterminous U. S.
Click on the map for a larger image.







Landslide hazard maps typically aim to predict where failures are likely to occur without any clear indication of when they are likely to occur.  They are useful for providing landslide hazard information needed for planning and protection purposes.  An ideal map of slope instability hazard should reflect information concerning at least the following variables:


 

Temporal probability requires the analysis of potential triggering factors (earthquakes, threshold precipitation, etc.) in relation to the landslides and the application of complex prediction models.  Triggering factors, however, cannot be predicted.  For this reason, most landslide hazard models typically show spatial probability without regard for temporal probability.
 

Input data required in physically-based prediction models often varies from location to location, which causes problems when trying to develop a model for a large area.  Some alternatives to landslide hazard maps are listed below, but it is in no way a comprehensive list of the numerous methods available for predicting landslide occurrence.

Landslide Inventory Map
A typical landslide inventory map is based on aerial photograph interpretation, ground survey, and/or a database of historical movements within the area.  The product of a landslide inventory map is a spatial distribution of landslides as points or to scale.  Landslide inventory maps can and often are used as a basis for other landslide hazard zonation techniques or an elementary form of a hazard map.  These maps, however, only provide information for a short period of time, and they provide not insight into temporal changes in landslide distribution.


Landslide overview map of the Conterminous United States.
Click on the map for a larger image.

Landslide Activity Map
A landslide activity map is a refinement of the landslide inventory map.  It is based almost solely on multitemporal aerial photograph interpretation.
 

Geomorphological Method Map
A Geomorphological method map is produced by mapping  movements in their geomorphological setting.  This can be done from aerial photos, satellite/RADAR images, etc.  A degree of hazard is allocated at each site in the terrain, but the rules of decision change from place to place (and from person to person), which often leads to a map which is very subjective.
 

Statistical Techniques
Statistical techniques aim at a higher degree of objectivity and better reproducibility of hazard zonation.  There are many statistical methods used in this field.
 
 

GIS in analysis and prediction of landslides
A large database is necessary for the analysis and prediction of slope failures.  It needs to be able to store, manipulate, and apply the data collected in first two stages (recognition and monitoring).  A Geographical Information System is ideal for this stage in a landslide investigation because it is capable of handling large amounts of past, present and future data and integrating this data with predictions.  It is capable of data storage and visualization, it is cheaper and easier to use than a manual map production and overlay, it can have regional databases, and therefor perform both local and regional modeling.  There are many types of GIS packages which differ in terms of hardware requirements, potential of spatial functions, efficiency of the data-base, and internal data structure.
 
 
 

Conclusions

Remote sensing techniques greatly aid in the investigations of landslides, on both a local and regional scale.  Although they do not replace fieldwork, interdisciplinary research strategies, and testing  the reliability of landslide prediction models, remote sensing techniques do offer an additional tool from which we can extract information about landslide causes and occurrences.  Most importantly, they greatly aid in the prediction of future landslide occurrences, which is very important to those who reside in areas surrounded by unstable slopes.
 

Landslide and Geomorphology Links:
 U.S. Geological Survey Geologic Hazards Landslide Page
 Landslide Publications and Reports
The Virtual Geomorphology
Landslide Images
Landslide Publications and Reports
San Francisco Bay Area Landslide Maps
State Information for Landslides in Your Area
 
 



Questions? Comments? E-mail me at:   sloper1@hotmail.com


Click here for a bibliography related to this topic
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