Spatial Changes of Pre- and Post-war City : Mariupol (Using Supervized Classification - GEE and ArcGIS Pro mixed method)
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Spatial Changes of Pre- and Post-war City: Mariupol (arcgis.com)
Introduction:
The Russian invasion in Ukraine started around February 2022. Kyiv city was the first city invaded, followed by Mariupol, Sumy, Kharkiv, and Kherson cities as of March 2022. Three major periods and areas affected by the Russian invasion are represented in the map: [1-1] Stage 1: as of Feb. 2022; [1-2] Stage 2: as of October 2022; and [1-3] Stage 3: as of March 2023 (Source: BBC News, 2023).
In this story, the city of Mariupol is selected to identify the spatial changes between two distinct periods: [2-1] pre-war (July, 01-30th, 2021); and [2-2] post-war (July, 01-30th, 2022) periods. The classification of spatial changes includes seven categories, namely, urban, industrial, undeveloped lands, green/forest area, war-affected zones, agricultural fields (see the "methodology" section for details).
Methodology:
Satellite imagery data used is an API format provided by Google Earth Engine Platform. The satellite imageries provided are taken by the COPERNICUS satellite, and its surface reflectance data (level-2 data) is named as "Harmonized Sentinel-2 MSI: Multispectral Instrument, Level-2A" (the data provided are 10-30m resolution).
The supervised classification tool embedded in the GEE platform trains the classifier (using extracted sample) using classifier.train(). It classifies an Image or a "FeatureCollection" using "classify()" function. The algorithm embedded uses the "Classification and Regression Trees (CART) classifier" method (Breiman et al. 1984) to predict simple classes and areas identified under the "same" class (or category). The details of the methodology is represented in the next page.
Conclusion:
The result of GEE classification enabled the identification of war-affected zones in Mariupol city, with an overall accuracy of 83%. However, due to limitation such as spatial resolution, subtle images such as war-affected single-detached housings are not identifiable from the provided (open) data, the Harmonized Sentinel-2 MSI: Multispectral Instrument, Level-2A data.