Multi-Sensor Geospatial Integration of WSF, WSF3D, and WPE satellite imagery for 3D Urban Growth and Population Estimation in Kolkata, India

Rapid and unplanned urbanization has transformed the spatial and structural configuration of cities worldwide, particularly across the Global South, where high-resolution, multi-dimensional urban data remain scarce. Recent advancements in the World Settlement Footprint (WSF) and WorldPop Estimation (WPE) datasets have enabled detailed global assessments of dynamic urban growth, morphological evolution, and population estimation. However, the prime objective of the research is to integrate these multidimensional datasets to examine the coupled evolution of built-up area, volume, height, fraction, and population density in the fast-growing South Asian megacity of Kolkata, India.

This study bridges that gap by employing WSF2015 and WSF2019 derived through Landsat and Sentinel-1 image fusion using the Symbolic Machine Learning (SML) approach to quantify horizontal impervious expansion, alongside WSF3D 2023 produced using TanDEM-X, Sentinel-1, and Copernicus DEM to assess vertical urban growth in terms of building area, height, fraction, and volume at 90 m resolution. The WorldPop Estimation (WPE, 2000-2020) dataset, developed using a Random Forest-based dasymetric mapping algorithm and machine learning approach, provided 100 m population grids for demographic interpretation. All datasets were harmonized, processed, and spatially andstatistically analyzed in Google Earth Engine (GEE) and ArcGIS to generate spatiotemporal 3D urban growth dynamics.

Findings reveal a significant rise in mean building height (16.3 m) and built-up volume (696 m³ per pixel) up to 2023, coupled with an increase in mean population density from 321 to 447 persons per 100 m pixel (2000-2020). These results illustrate a strong linkage between vertical and horizontal densification and demographic intensification. The integrated WSF-WSF3D-WPE framework offers a scalable, open-data-driven methodology for 3D urban mapping, population–infrastructure coupling, and sustainability assessment, providing actionable insights for urban geo-environmental and socioeconomic planning in Kolkata and comparable megacities of the Global South for sustainable city development.