Surface water masks over the Mekong Delta and Cambodia derived from SAR Sentinel-1

27/07/2017

Introduction

We introduce a regular (twice a month) surface water masks for the Mekong Delta and Cambodia, derived from active microwave SAR Sentinel-1 satellite observations. Surface water masks were built based on a neural network classification trained on Landsat-8 optical data. Surface water masks are projected to the geographical latitude/longitude projection, between latitude: 8.5°N-13.5°N, longitude: 103°E-107°E. Surface water masks have 30-m spatial resolution, available from February 2015. Due to the lack of data, there is only one surface water mask per month between February and September 2015, then we get twice products per month from October 2015 until present time (24 masks per year). Monthly surface water maps for the year 2016 over the Mekong Delta and Cambodia are shown in Figure 1
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Figure 1. Monthly surface water masks over the Vietnam Mekong Delta and Cambodia for 2016. 
 

Methodology

Our algorithm is presented in Figure 2. A Neural Network (NN) is trained to find the relationship between the input (containing 7 parameters derived from SAR Sentinel-1 observations) and the output (reference surface water maps derived from Landsat-8 optical observations). The training is done once for all.  
A predicted surface water map can be produced for each new SAR overpass of the region. The NN method is very fast to apply once new raw SAR Sentinel-1 data are available. Details of the NN structure can be found in the paper1.
 
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Figure 2. The block diagram of the Neural Network algorithm

Evaluation

SAR Sentinel-1 surface water masks over the Mekong Delta and Cambodia have been are compared to:
  • Surface water maps derived from Landsat-8 optical observations
  • Surface water maps derived from MODIS optical observations
  • Topography-based flood-ability index
These comparisons showed good agreements between the SAR estimates and the other products.

Applications

This product can be used to monitor and quantify surface water under all weather conditions within the Mekong Delta and Cambodia. It can also be an input for regional hydrological models.

Data download

Data files are stored in the Google Driver. Data Folder
http://drive.google.com/drive/folders/0B_KOtu1oX8p2alR5UmdoY1Z0SFk?usp=sharing

The size of a data file is ~ 134 MB.
A data file contains 3 states: 0 for non-water pixels, 1 for water pixels, and -1 for non-analyzed pixels (including pixels located over ocean).

Citation

  1. Binh Pham-Duc, Catherine Prigent, Filipe Aires: Surface water monitoring within Cambodia and the Vietnamese Mekong Delta over a year, with Sentinel-1 SAR observations. Water 05/2017. DOI:10.3390/w9060366

Questions can be sent to PHAM Duc Binh ([email protected])