Merge pull request #320 from willrayeo/sen-1-flood-vis

Sentinel-1 flood visualisation script to add

data-fusion/data-fusion.md

@@ -23,3 +23,4 @@ The combination of multiple remote sensing data sources can provide invaluable i
  - [Sand-Oriented Land Cover Classification with Sentinel-1 and Sentinel-2](/data-fusion/sand-oriented_land_cover_classification_s1_s2)
  - [Thermal visualization and water in wetlands with Landsat 8 L1 & L2](/data-fusion/thermal_visualization_and_water_in_wetlands)
  - [Land Surface Temperature with S3 SLSTR and OLCI](/sentinel-3/land_surface_temperature)
+ - [Visualising floods using Sentinel-1 overlaid on Sentinel-2 imagery](/data-fusion/s1_flooding_visualisation/)

data-fusion/s1_flooding_visualisation/README.md

@@ -0,0 +1,25 @@
+---
+title: Visualising floods using Sentinel-1 overlaid on Sentinel-2 imagery
+parent: Data Fusion
+layout: script
+permalink: /data-fusion/s1_flooding_visualisation/
+nav_exclude: true
+---
+
+
+## Authors
+
+**Author of the datafusion script:**
+- William Ray & Maxim Lamare
+
+## Evaluate and visualize  
+ - [EO Browser](https://sentinelshare.page.link/i2yk)
+
+## General description of the script  
+
+This script can be used to visualise flood events using Sentinel-1 GRD imagery. This is especially useful for areas of interest that are affected by cloud cover (common during flood events caused by excessive rainfall). The script uses a threshold of -15 decibels to classify flooded pixels. This value can be adjusted to suit your area of interest. In addition, to help the viewer orientate themselves, a clear Sentinel-2 image is used as the basemap for this visualisation so that it can be easily interpreted where the flood extent reaches for those unfamiliar with interpreting SAR images. 
+
+## Description of representative images  
+
+**Flooding in the UK 28th January 2021**
+![flooding](fig/fig1.jpg) 

data-fusion/s1_flooding_visualisation/script.js

@@ -0,0 +1,31 @@
+//VERSION=3
+function setup() {
+  return {
+    input: [{
+        datasource: "S2L2A",
+        bands: ["B08", "B03", "B04", "CLM", "CLP"]
+      },
+      {
+        datasource: "S1GRD",
+        bands: ["VV", "VH", "dataMask"]
+      }
+    ],
+    output: { bands: 4 },
+    mosaicking: "SIMPLE"
+  };
+}
+
+function toDB(input){
+  return 10 * Math.log(input)/Math.LN10;
+}
+
+function evaluatePixel(sample) {
+  var S1 = sample.S1GRD[0];
+  var S2 = sample.S2L2A[0];
+  if (toDB(S1.VV) <= -15){
+    return [S1.VV * 10, S1.VV * 10 , S1.VV * 50, 1];
+  } else {
+    const f = 2.5;
+    return [f*S2.B08,f*S2.B08, f*S2.B08,1]
+  }
+}