This document describes a concept for detecting water bodies from TanDEM-X radar data. The goal is to produce a global water indication mask to help process the TanDEM-X digital elevation model. The method uses amplitude and coherence images with filtering and thresholding to identify water pixels while excluding other areas like desert or steep terrain. An evaluation on a test site of the River Elbe showed the method could correctly identify over 80% of water bodies larger than 1 hectare when combining amplitude and coherence data. Future work will assess the method in different climate zones and produce a mosaicked global water mask product to help further process the TanDEM-X DEM.

1. Water Body Detection from TanDEM-X Data: concept & first evaluation of an accurate water indication mask A. Wendleder 1) , M. Breunig 1) , K. Martin 2) , B. Wessel 1) , A. Roth 1) 1) German Aerospace Center DLR | 2) Company for Remote Sensing and Environmental Research SLU IGARSS 2011 / Vancouver / 2011-07-28 IGARSS’11, Vancouver

2. Outline Introduction Definition of the TanDEM-X water indication mask Challenges for TanDEM-X water body detection Concept & methodology of water body detection Test site demonstration Evaluation of classification results Outlook Slide

3. Definition of the TanDEM-X water indication mask Global mission – global DEM – global water body mask Water body mask primarily extracted for post-processing DEM editing ongoing work in flattening of outpoking water bodies correct orthorectification of remote sensing data No production of a complete global water body inventory Slide Kurnool Kadapa Channel / India frozen Lake Taimyr / Russia

4. Challenges for TanDEM-X water body detection TanDEM-X mission with 2 global acquisition data sets in 2011 & 2012 The water body detection runs completely data-driven Processing at Raw DEM level (30*50 km ≈ 8.000*10.000 pixels) 400 up to 800 Raw DEM per day to be processed Therefore maximum computing time of 3 minutes per product Applicable for different appearances of water bodies worldwide (coastline, inland lake, river, tropical, arctic, arid or humide climates etc.) Slide tropical river & coastline in Indonesia small inland water bodies in Minnesota / USA

5. Concept & Methodology (I) Input images are amplitude & coherence image Exclusion of desert & polar regions SRTM WAM MODIS/Terra Land Cover Types Exclusion of steep terrain SRTM DEM Slide

6. Concept & Methodology (II) Slide Median filter separately applied both to amplitude & coherence image Threshold method with fix threshold values Two different thresholds to handle complexity of water appearance 1. threshold: reliable classification 2. threshold: potential classification Calculation of water body areas via Chain Code and elimination of water bodies < 1 hectare Fusion of three intermediate water body layers

7. Test site demonstration River Elbe, Hamburg, Germany acquired on January 27, 2011 Incidence angle 43.4° to 45.7° Slide

8. Evaluation of classification results (I) Slide Calculation of completeness and correctness reference vector layer data of digital landscape models from the Authoritative Topographic Cartographic Information System (ATKIS)

9. Evaluation of classification results (II) Slide ATKIS: Authoritative Topographic Cartographic Information System Reference Completeness Correctness Amplitude ATKIS 86.9 % 92.6 % ATKIS water bodies > 1hectare 88.1 % 92.5 % Coherence ATKIS 79.8 % 98.7 % ATKIS water bodies > 1hectare 80.9 % 98.7 %

10. Evaluation of classification results (III) Water body mask derived of amplitude image rich in detail susceptible to misclassifications Water body mask derived of coherence image significant and robust results loss of details of small scale water bodies Maximum of a correct & complete water mask with combination of both Slide

11. Outlook Accuracy assessment of the water body detection for different climate zones robustness & global transferability of our approach Mosaicking of different water bodies (neighboring acquisitions resp. first & second year acquisition) to an intermediate & final TanDEM-X water body mask product TanDEM-X DEM editing using TanDEM-X water body mask flattening of outpoking water bodies Slide

12. Slide River Elbe, Hamburg, Germany SAR image Water indication mask DEM edited DEM

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14. Slide Thank you for your attention! Anna Wendleder | Markus Breunig German Remote Sensing Data Center Team SAR Topography Phone: +49 8153 28 3439 Email: Anna.Wendleder@dlr.de | Markus.Breunig@dlr.de