abeylicious/Maiduguri-flood-sar-2024-changes
Domaine:
geospatialenvironment and energyType de record:
project
Créateur:
abe
Hôte:
Cloud-proof Synthetic Aperture Radar (SAR) flood mapping pipeline in Google Earth Engine using Sentinel-1 C-band (VV polarization) to quantify urban inundation from the September 2024 Alau Dam collapse in Maiduguri, Nigeria
# Satellite Radar (SAR) Flood Extent Mapping: Maiduguri 2024
> 📖 **Read the full step-by-step case study on Medium:** Cloud-Proof Flood Extent Mapping with Sentinel-1 SAR in Google Earth Engine
## Overview
This repository contains a cloud-proof Synthetic Aperture Radar (SAR) change-detection pipeline implemented in **Google Earth Engine (GEE)** to quantify the flood inundation caused by the **Alau Dam collapse in Maiduguri, Borno State, Nigeria (September 2024)**.
Because standard optical sensors (e.g., Sentinel-2, Landsat) were obstructed by heavy monsoonal cloud cover during the event, **Sentinel-1 C-band Synthetic Aperture Radar (GRD, VV Polarization)** was utilized to penetrate clouds and map open surface water extent.
---
## Key Results & Metrics
* **Pre-Flood Baseline:** July 1 – August 25, 2024
* **Post-Flood Assessment Window:** September 5 – September 25, 2024
* **Optimal Backscatter Threshold:** `-16 dB` (VV Polarization)
* **Calculated Surface Inundation Area:** **~20 km²** within the metropolitan ROI
---
## Methodology & Workflow
1. **ROI Definition:** Maiduguri Metropolis, Alau Dam reservoir, Ngadda River channel, and the downstream Jere Bowl.
2. **SAR Filtering:** Sentinel-1 IW (Interferometric Wide Swath) mode in `VV` polarization.
3. **Temporal Compositing:** Median reductions for baseline and immediate post-breach periods to minimize radar speckle.
4. **Thresholding & Masking:** Backscatter threshold applied at `-16 dB` to segment calm surface water.
5. **Change Detection:** Spatial logic isolating newly inundated pixels while excluding permanent water bodies:
$$\text{Flood Extent} = \text{Water}_{\text{Sept}} \land \neg \text{Water}_{\text{August}}$$
6. **Area Reduction:** Spatial aggregation using `ee.Reducer.sum()` at 10 m native pixel resolution.
---
## Threshold Calibration & Sensitivity Analysis
A sensitivity comparison was conducted to eliminate dry soil/sand false positives in semi-arid terrain:
| Threshold | Calculated Inund …