Merge pull request #301 from dipankar05/patch-1

Update script.js

Author: chorng

sentinel-1/radar_vegetation_index/README.md

@@ -22,7 +22,7 @@ examples:
   platform:
   - CDSE
   - EOB
-  evalscript: 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
+  evalscripturl: https://custom-scripts.sentinel-hub.com/sentinel-1/radar_vegetation_index/eob.js
 ---
 
 ## General description of the script

sentinel-1/radar_vegetation_index/eob.js

@@ -23,15 +23,27 @@ const ramp = [
 const visualizer = new ColorRampVisualizer(ramp);
 
 function evaluatePixel(samples) {
-    let dop = (samples.VV / (samples.VV + samples.VH));
-    let m = 1 - dop;
+    //equivalent to complement of the degree of polarization
+    // Ratio parameter
+    let q =  (samples.VH / samples.VV);
+
+    // co-pol purity parameter m
+    // m = (1-q)/(1+q)
+    // normalized co-pol intensity parameter beta
+    // beta = 1/(1+q)
+    // Dual-pol radar vegetation indec DpRVIc = 1-(m*beta)
+    // It can be also written directly in terms of q as follows
+    let N = q*(q+3);
+    let D = (q+1)*(q+1);
+
     //depolarization within the vegetation
-    let val = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+    //let val = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+    let val = N/D;
+
     // The library for tiffs works well only if there is only one channel returned.
     // So we encode the "no data" as NaN here and ignore NaNs on frontend.
     const indexVal = samples.dataMask === 1 ? val : NaN;
     const imgVals = visualizer.process(val);
-
     return {
         default: imgVals.concat(samples.dataMask),
         index: [indexVal],

sentinel-1/radar_vegetation_index/raw.js

@@ -10,9 +10,20 @@ function setup() {
 
 function evaluatePixel(samples) {
     //equivalent to complement of the degree of polarization
-    let dop = (samples.VV / (samples.VV + samples.VH));
-    let m = 1 - dop;
+    // Ratio parameter
+    let q =  (samples.VH / samples.VV);
+
+    // co-pol purity parameter m
+    // m = (1-q)/(1+q)
+    // normalized co-pol intensity parameter beta
+    // beta = 1/(1+q)
+    // Dual-pol radar vegetation indec DpRVIc = 1-(m*beta)
+    // It can be also written directly in terms of q as follows
+    let N = q*(q+3);
+    let D = (q+1)*(q+1);
+
     //depolarization within the vegetation
-    let value = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+    //let value = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+    let value = N/D;
     return [value]
 }

sentinel-1/radar_vegetation_index/script.js

@@ -1,6 +1,7 @@
 // Radar vegetation index for Sentinel-1 (RVI4S1) SAR data
 // Institute: MRSLab, Indian Institute of Technology Bombay, India
 // Data requirements: Sentinel-1 GRD data
+// Reference: Bhogapurapu, N., Dey, S., Mandal, D., Bhattacharya, A., Karthikeyan, L., McNairn, H. and Rao, Y.S., 2022. Soil moisture retrieval over croplands using dual-pol L-band GRD SAR data. Remote Sensing of Environment, 271, p.112900.
 function setup() {
    return {
       input: ["VV", "VH", "dataMask"],
@@ -20,10 +21,21 @@ const visualizer = new ColorRampVisualizer(ramp);
 
 function evaluatePixel(samples) {
    //equivalent to complement of the degree of polarization
-   let dop = (samples.VV / (samples.VV + samples.VH));
-   let m = 1 - dop;
+   // Ratio parameter
+   let q =  (samples.VH / samples.VV);
+
+   // co-pol purity parameter m
+   // m = (1-q)/(1+q)
+   // normalized co-pol intensity parameter beta
+   // beta = 1/(1+q)
+   // Dual-pol radar vegetation indec DpRVIc = 1-(m*beta)
+   // It can be also written directly in terms of q as follows
+   let N = q*(q+3);
+   let D = (q+1)*(q+1);
+
    //depolarization within the vegetation
-   let value = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+   //let value = (Math.sqrt(dop)) * ((4 * (samples.VH)) / (samples.VV + samples.VH));
+   let value = N/D;
    let imgVals = visualizer.process(value);
    return imgVals.concat(samples.dataMask)
 }