Disaster Risk Reduction, Imagery, Mapping

Satellite Imagery is A Powerful Visual Aid in GIS and Disaster Response

The earthquake events of August 21, 2018 which shook Venezuela, Trinidad and other neighbouring countries (https://www.usgs.gov/news/magnitude-73-earthquake-venezuela) reminded me that not all disasters can be predicted or come with a warning. Videos which showed the impact of the earthquake quickly filled my social media timeline, causing me to reflect on the training I had undergone as project manager for the International Charter Space and Natural Disasters (https://disasterscharter.org). This organization, once registered with, provides a series of support through the use of satellite imagery to assist in the aftermath of a disaster.

Satellite imagery is a form of remotely sensed data with proves useful in the occurrence of an unforeseen event and provides a powerful visual aid when utilized with a geographic information system (GIS). Disaster risk managers are better able to assess their region’s risk when they are able to compare pre and post disaster images.  This type of analysis enables relief workers to identify changes in the landscape, such as buildings which are no longer standing and roads which are obstructed. It is an efficient way to identify damage and conduct rapid impact and needs assesments. GIS supports the use of satellite imagery to locate damaged facilities, identify the type and amount of damage and begin to establish priorities for action.

As satellite sensors improve, satellite imagery is becoming more useful. One of my favourite places to explore satellite data is the USGS Earth Explorer Portal (https://earthexplorer.usgs.gov/). It provides an interface where one can search the available sensors to see the data that is available for a particular area of interest. The advantage of the USGS Earth Explorer is that it houses data from the Landsat Programme which has a 40+ year track record of image acquisition. It allows for free downloading of data over chronological timelines while providing a long list of satellites to choose from.

Additionally, capturing my interest for hours on end is the USGS Earth Now Viewer (https://earthnow.usgs.gov/observer). This viewer is truly remarkable as it shows the position of the Landsat sensor in real-time. It also gives a visual of the satellite images being collected when the sensor scans the earth.

The Landsat Program began with Landsat-1 in 1972 and Landsat- 9 is planned for 2023. Over the years, Landsat has enhanced the number of spectral bands, spatial resolution and spectral resolution. Landsat 1-3 sensors collected data in only 4 bands and at 60 meter resolution. Over time, this has improved, as Landsat 8 now collects in 11 spectral bands varying from 15 meter to 100 meter.

The Sentinel Satellites of the Copernicus Programme also provide free satellite imagery which can be downloaded at the Copernicus Open Access Hub (https://scihub.copernicus.eu/dhus/#/home). The Sentinel-2 provides some improvement to the Landsat data with sharper imagery of up to 10 meters. Sentinel-2 monitors more frequently with a revisit time of 5 days and captures land changes in 12 spectral bands, each ranging from 10 – 60 meters pixel size. The USGS Sentinel2Look Viewer (https://landsatlook.usgs.gov/sentinel2/viewer.html) allowed me to browse through some sentinel-2 imagery. I found relatively cloud free imagery of Montserrat (shown below) which was acquired on 12th April 2018. This is a plus as cloud-free imagery is not always available due to our location and climate.

With the assistance of a skilled technician, satellite imagery can be utilized effectively in disaster management especially during the response stages. By combining spectral bands and performing image classification techniques the capabilities of remotely sensed data can be fully utilized in disaster management.

 

Lavern Rogers-Ryan is a geospatial consultant specialising in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.

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