Flood Mapping using Sentinel-1 SAR data in Google Earth engine - Recent Assam flood

This video will take you through the entire process of building a script for visualizing and mapping floods using Sentinel-1 dataset in Google Earth Engine for Golpara district of Assam.
Google Earth Engine is a geospatial processing service. With Earth Engine, you can perform geospatial processing at scale, powered by Google Cloud Platform. The purpose of Earth Engine is to:
-Provide an interactive platform for geospatial algorithm development at scale
-Enable high-impact, data-driven science
-Make substantive progress on global challenges that involve large geospatial datasets
Also, In the later part of the video it is shown, how to create earth engine app. Apps published from Earth Engine are accessible from the application-specific URL generated at time of publishing. No Earth Engine account is required to view or interact with a published App.
Resources:
- Earth Engine script used in video - code.earthengine.google.com/c...
- Earth Engine App cretaed in the video: opengeolab4.users.earthengine...
- Earth engine Link - earthengine.google.com/

[@JohnLee-kh2wi]

very good resources about GEE Sentinel-1

[@geykum_shakeshigh]

Thank you for the tutorial

[@supriyakamoji97]

Good Tutorial

[@mafijulislam1684]

nice sir

[@olorunfemiomonigbehin389]

This is amazing work. My question is, how can we add different water levels to the analysis to get the amount of inundation at different water levels. Thank you.

[@anamkhalid8700]

Very good tutorial. Sir, I have a question, what is the decibel value range for water and for vegetation?

[@aravindbobbili194]

sir, how can we use ostu thresholding techniques to determine optimum thresholding technique to determine flood inundation mapping?

[@sarb3470]

I am trying to run this for other area of interest, but not working with message"Cannot read properties of null (reading 'coordinates')", please help.

[@sharminara5862]

This is a great tutorial. I am having an issue with the Flood Area calculation. Can you please help me in this regard?

[@dharanisampath6509]

Hi, I need help, I want to find out the number of water and non-water pixels on the image for satellite data available date-wise for sentinel 1 and sentinel 2, Landsat 8, and MODIS. For example, if I have 200 water bodies, I'm getting the total number of pixels for all 200 water bodies but I need individual water bodies' water and non-water pixels' satellite data available date-wise. help me, how can I do that?

[@hientranthi9973]

Using your code line 35 had an error notification and won't run (dt.geometry is not a function) Hope you can answer Thanks very much!

[@kouameelyasskanga2337]

How can we import sentinel-1 images of our study area? the variable ind_dt what is its purpose?

[@greeshmaranjith6279]

Hi I tried exporting the flood mask to drive and then to arcgis, but image is full black. Is it because band VH

[@bhanupriya9966]

can you provide the link to download the shape that is being used in the video

[@kouameelyasskanga2337]

In the Assets tab, I don't have the same files as you

[@HAMZABUTT-um1wc]

what will be function for export flooded area in polygon shapefile

[@donugift9144]

var before_filtered = ee.Image(toDB(RefinedLee(toNatural(before_image)))). I ran into an error on this line stating "toDB is not defined" try to modify the code to no avail. kindly help to respond what may be wrong?

[@Sathish69]

thank you sir your teaching, sir when i used to export the data like this error showing before run how could i resolve it 'A mapped function's arguments cannot be used in client-side operations'

[@g-sigtimor-leste]

How to classify level of flood such a High, Medium and Low?......

[@MaalavsEnchante]

hi..I understand that if the after_filtered image value is less than -20 db is flood but why before_filtered image is greater than -20 db is considered as flood? Additionally, you said to take before 1 and before 2,but the value you mentioned is less than -20, should not be value be greater than -20 fore before2_filtered image?

[@OpenGeoLab]

We are taking two images one is before event and one is post event...if water is not there in before image...and water comes suddenly after event.. you can change this value ..for before image based upon the area You can also calculate the ratio of the two images and then do the thresholding..

[@AbuZafor-yy5qh]

How could we export it sir?

[@yathestsharma1942]

can you provide shapefiles of all the districts

[@mdmahabubarefinchowdhury7944]

Hi, nice work. I have a question. What is the unit? is that 25m?

[@OpenGeoLab]

10 m

[@mrfaizi2450]

Dear did you used otsu thresholding method?

[@OpenGeoLab]

I have used simple thresholding based on the the backscatter values of SAR data..and for flood detection i have used backscatter values for water..

[@pulaharoy1424]

Very good tutorial. Can I please get in touch with you? I’m a data journalist in a magazine and was wondering if I can do this in QGIS as well? Or how do I export the image in .tiff?

[@OpenGeoLab]

Use this piece of code for exporting the image to your Google drive. Export.image.toDrive({ image: image_name, description: 'Sentinel1', scale: 10, maxPixels: 10000000000000, region: your_region }) Image will be uploaded in Google Drive and from there you can download. Yes you can do the same analysis in qgis using raster calculator, but you have download before and after images.. It is better to do the analysis in the earthengine and export the final output Also qgis has earth engine plugin...that you can also use.

[@pulaharoy1424]

@@OpenGeoLab Hello, thanks for getting back. I just mailed you some queries. Can I please talk to you once? Thank you.

[@godwinsolomon9108]

​@OpenGeoLab sir where can i get the indian district sorted data sets

[@coolsamuel4354]

Using your code line 15 had an error notification and won't run

[@HBR2727]

I have problem on this line can you help>>>>>>>var before = collection.filter(ee.Filter.date('2022-05-01','2022-05-10')).filterBounds(dt)

[@godwinsolomon9108]

sir where can i get the indian diatrict sorted data file

[@ayeshamunasinghe742]

Thanks for the resource. I have a question. There are many thresholding methods to detect flood and permanent water bodies. is there any specific name for this thresholding method?

[@OpenGeoLab]

No, it is simple thresholding...you can use ratio also for mapping the change in the backscatter...

[@ayeshamunasinghe742]

@@OpenGeoLab Thank you

[@vinod9991]

Sir how to implement the concept of region growing here.. To enhance the accuracy

[@OpenGeoLab]

You use the classification algothim I.e random forest, SVM etc in GEE just you have to generate some training samples to train the ML algorithm . I have uploaded a video for classification of rice crop using SAR data in GEE you follow that for classification..

[@mayurichetia3890]

Sir, I a imported a district shapefile which I have extracted in arcgis softwere from the districts shapefile of assam. But after importing and applying the script no result is shown there and I found that in the columns there are only 6 properties instead of 7 and on the result section of image collection the values are missing. Sir can you tell me how I will get the correct shapefile to get the result.

[@OpenGeoLab]

Please make sure....projection of the shapefile...is in EPSG:4326

[@mayurichetia3890]

Thank you so much sir, Sir can I get the code to export the map to drive?

[@OpenGeoLab]

Use this piece of code for exporting the image to your Google drive. Export.image.toDrive({ image: image_name, description: 'Sentinel1', scale: 10, maxPixels: 10000000000000, region: your_region }) Image will be uploaded in Google Drive and from there you can download.

[@mayurichetia3890]

I'm grateful, sir. The tutorial is indeed very useful. You're doing a great work and I appreciate your kind words and help. 😊😇

[@marcorivera4020]

@OpenGeo Lab I'm sorry I'm very new to GEE, I just replicate the code on the video but I'm still struggling to find what's the variable name we should replace instead of image_name to get the flooded area and the water body area exported?

[@kamalkushwah7512]

How to export flood before and after image

[@OpenGeoLab]

Use this piece of code for exporting the image to your Google drive. Export.image.toDrive({ image: image_name, description: 'Sentinel1', scale: 10, maxPixels: 10000000000000, region: your_region }) Image will be uploaded in Google Drive and from there you can download.

[@phornnayelin8429]

Can you show me how to export flood inundation and water body in Raster and vector data please

[@OpenGeoLab]

Use this piece of code for exporting the image to your Google drive. Export.image.toDrive({ image: image_name, description: 'Sentinel1', scale: 10, maxPixels: 10000000000000, region: your_region }) Image will be uploaded in Google Drive and from there you can download as raster file..then you can convert raster to vector in any open source gis software I.e QGIS

[@AshwinShiraskar]

can u send me the full code

[@somsaybiosoulikhan5721]

can I have your code that was edited? thank

[@OpenGeoLab]

Link for the code is in the description of the video...... Also you can check..this www.linkedin.com/posts/karanknit_assamfloodmap1-activity-6934938885693026304-6TuW?

[@somsaybiosoulikhan5721]

@@OpenGeoLab thanks so much

[@user-kk4ni4rg7v]

Hello Sir Can you share to me this script ? that is important for me Thanks

[@OpenGeoLab]

Script link is in the description of he video

[@user-kk4ni4rg7v]

@@OpenGeoLab thank you so much Sir

[@user-kk4ni4rg7v]

can you share to me export scrip for this

[@soirleumas]

volver a mirar, dont understand

[@mohammadshujanabeel]

// Detect flood and water using the provided logic var flood = before_filtered.gt(-20).and(after_filtered.lt(-20)); @OpenGeo Lab Why we are using 20? Also explain the line

[@aimenfatima6537]

The link to your app is not working, it shows the USA map and even if i drag towards Assam , there is nothing there. This also happened when i followed the tutorial and made my own project. The code runs but the app shows nothing. Could you help? @opengeo lab

[@OpenGeoLab]

You have to replace the shapefile as per your area ...check this updated code code.earthengine.google.com/1fb758f0267e39565409cb08dc5416aa

[@aimenfatima6537]

@@OpenGeoLab i do have my own shapfile. Its working in the API. When i run the code, it centers around my region amd shows all the data. But when i upload as an app, it shows nothing

[@OpenGeoLab]

@@aimenfatima6537 ok when you publish as app..it will take few minutes after publishing..try to access the app after few minutes..

[@aimenfatima6537]

@@OpenGeoLab its been more than a day, its still the same

[@aimenfatima6537]

@@OpenGeoLab can i email/contact you?

[@sarb3470]

after adding the area of interest this message is showing = ImageCollection COPERNICUS/S1_GRD (0 elements), please help. Why 0 element is showing?

[@OpenGeoLab]

there was a problem in the district boundary shapefile attributes, i have updated the link in the description of the video it will work now. code.earthengine.google.com/c150dffea355475b543a96ac9cdfffb0

[@sarb3470]

@@OpenGeoLab yes, now it is working, thak you for your response

[@ankitchandelia1603]

@@OpenGeoLab Sir, it isn't working. Kindly tell what problem was there in shapefile attributes.