- Amadou IBRAHIM
Satellite imagery in a humanitarian context??? Here is a practical application in conflict zones
Updated: Dec 5, 2020
Man has always sought to locate himself in time and space, to discover his territory in order to better know and understand his environment. He began by drawing maps of the earth and its universe until today, harnessing new technologies for a more detailed representation of the earth.
1. The basics of satellite imagery
A satellite image can be defined as a photograph of a portion or all of the earth taken by a satellite in orbit.
With the multiplication of satellites in orbit, the offer of satellite images is becoming large and accessible. You can find two categories of satellite images:
1. Low and medium resolution images: the resolution of which varies from kilometers to a few meters. They are used, for example, to assess the level of vegetation (NDVI), for weather forecasts or the identification of burnt areas.
Source: Biomass anomaly (NDVI) 2020, pixel size spatial resolution 1 Km
2. The high and very high resolution images offer much more details with a resolution that varies from meter to centimeter. They are used in studies on the urban environment, for example, or in the agricultural sector.
Source: Satellite image showing a locality in the vicinity of Bamako Google Earth, image resolution, 50 cm, February 2020
Low, medium and high resolution satellite images are free and accessible on the most popular Google Earth Engine (GEE) platform. On the other hand, very high resolution satellite images are generally chargeable (some are nevertheless available free of charge on GEE) and with a high cost, up to around $ 20 per km2: they can be acquired from image suppliers and private companies.
Depending on the objective of your analysis and your program, you will first make the choice of:
1.the level of resolution of the satellite images you need
2.Check the availability of satellite images on your preferred platform
3. and you can finally then assess the associated cost (if you don’t find free satellite image).
We have tested and used high-resolution satellite imagery in the Sahel region, in Mali, to try to assess the impact of conflict on (household) livelihoods in areas where physical access (by humanitarian and state actors) was severely restricted due to insecurity. We looked at the agricultural areas cultivated over several years : this is what we called an "analysis of agricultural dynamics ”.
2. What does the analysis of a satellite image look like to assess agricultural dynamics?
We have detected the physical impacts of the conflict and the reduction or abandonment of crops lands, thanks to a global view over large geographical areas.
The two satellite images below are those of villages X and Y in the Koro circle, Mopti region (Country: Mali). This is the result of processing satellite imagery for the period from June to October for the years 2017 and 2019.
The black “spots” visible in the center of the satellite images correspond to the two villages.
On the first satellite image of 2017, cultivated fields are visible all around the villages within a radius of 5 km and even beyond: it is the dark blue or cyan rectangles that stand out from the surrounding natural vegetation, of a clearer color.
Source of satellite images: ESA / COPERNICUS, Sentinel-2. Composite products derived from 20 images acquired between June and October 2017
On the second satellite image of 2019, you can observe a considerable decrease in cultivated areas: they are more concentrated around the villages, within a radius of 1 to 2 km. Natural vegetation has grown back beyond this borderline.
Source of satellite images: ESA / COPERNICUS, Sentinel-2. Composite products derived from 20 images acquired between June and October 2019
The analysis of villages and agricultural areas made it possible to establish a classification of decreases or increases in agricultural area by locality according to their importance according to a qualitative assessment
1. How to enhance the analyzes of satellite imagery: mapping for appropriate communication to the general public
A map, beyond the aesthetic aspect, constitutes a simple means of visualizing spatial information and allows better accessibility, readability, understanding and use of information by all (see the post on the use of GIS).
The map below shows the results of the satellite analysis of the agricultural dynamics in the Mopti region (Mali) between 2017 and 2019.
Source: Mapping of agricultural dynamics between 2017 and 2019, WFP
The dots in yellow correspond to the localities for which a slight decrease in cultivated areas has been detected. The dots in orange and red correspond to villages with average and significant decreases in cultivated areas in 2019 compared to those in the years preceding the conflict (2016, 2017). The gray dots represent the villages where there was no visible change detected, while the green dots show the localities where increases in agricultural areas were observed.
The advantage of maps is that you can add other elements or factors that allow you to draw trends .
This analysis was combined with other food security indicators and the number of security events. The following results were found:
1. Results of analyzes by satellite imagery were confirmed and they highlighted the link between agricultural dynamics and impact on food security
2. The link between agricultural dynamics and conflicts was confirmed, depending on the typology or dynamics of the conflict
2. What next? Using mapping for decision making and other uses
Source: Refugee camp, Darfur, Google Earth
These analyzes were used for pre-targeting in conflict-affected areas for an emergency response and longer-term interventions and to support advocacy efforts.
Satellite imagery analyzes can be used in different contexts, such as:
• Detection of the potential impact of population movements - especially in areas of concentration of displaced populations or refugees: urbanization phenomenon or exploitation of natural resources
• Destruction (due to conflict or natural shocks) or creation of infrastructures (impact of population movements, impact of a program)
• The location of areas affected by floods (associated with rising rivers) or droughts
• the impact of fires or large-scale logging on natural and forest resources' availability
5. Basic but E-SSEN-TIAL reminders
TRIANGULATE the results of this type of analysis with other data sources: CROSSCHECK, COMBINE, CHECK AGAIN: you can use reports, (telephone) interviews with people who know well the area etc. A single source of data is usually not enough to assess a situation.
Check the SENSITIVITY of your data, your results and your maps before sharing your results widely (we are preparing an article on this). Are there any RISKS in sharing this information? Could these results harm and to whom?
6. Practically, where to start if you are interested in carrying out analysis by satellite imagery?
The use and exploitation of satellite images on GEE requires the creation and / or possession of a Gmail account, a technical expertise in computer coding (knowledge of the Java language) as well as an expertise in interpretation and analysis of images. satellite (remote sensing).
If you want to know more, CONTACT US!
This post was inspired by the document " WFP Mali - satellite imagery"
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Author : Amadou IBRAHIM, Geomaticien - Information Manager