Towards Global Monitoring of Soil Moisture at 1 km Spatial Resolution using Sentinel-1: Initial Results

Transcription

1 Towards Global Monitoring of Soil Moisture at 1 km Spatial Resolution using Sentinel-1: Initial Results W. Wagner, V. Naeimi, B. Bauer-Marschallinger, S. Cao, A. Dostalova, C. Notarnicola, F. Greifeneder, S. Paloscia, E. Santi, C. Rüdiger, M. Aspetsberger, S. Amberger, M. Täubler, C. Briese, R. Kidd

2 Motivation Coarse resolution active and passive microwave sensors operating in the frequency range from 1 to 10 GHz provide comparable and useful soil moisture data at km ASCAT, SMOS, AMSR-2, SMAP,... Overpass times at about 1:30, 6:00, 9:30, 13:30, 18:00, and 21:30 Merging and/or joint use of data sets has been shown to be favourably in applications An increasing number of applications demands soil moisture measurements at a spatial resolution of 1 km or finer Downscaling of coarse resolution microwave data with models and/or higher resolution remote sensing data Direct retrievals from high-resolution active microwave measurements Synthetic Aperture Radar (SAR) Loss of SMAP radar is very unfortunate

3 Maize field in Upper Austria end of August 2015

4 ENVISAT ASAR: Test Bed for Sentinel-1 Based on ASAR Images Sabel, D., Z. Bartalis, W. Wagner, M. Doubkova, J.-P. Klein (2012) Development of a Global Backscatter Model in support to the Sentinel-1 mission design, Remote Sensing of Environment, 120,

5 ASAR Soil Moisture ( ) ENVISAT ASAR Global Monitoring (GM) mode served as test bed for demonstrating soil moisture monitoring capabilities Full continents (Australia, Africa) have been processed NRT capabilities demonstrated Weaknesses Poor temporal coverage High radiometric noise Strengths High consistence with ASCAT and other global soil moisture products Spatial details not contained in ASCAT and passive sensors First continental-scale 1km soil moisture product produced by TU Wien in the ESA funded SHARE project

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7 ASAR versus ASCAT Soil Moisture Validation study over Denmark In-situ data from HOBE network ( ASAR GM data in HH polarisation at 1 km ASAR WS data in VV polarisation averaged to 1 km Soil moisture images over Northern Denmark from October 9th, 2007 Gruber et al. (2013) Potential of Sentinel-1 for high-resolution soil moisture monitoring, IGARSS 2013, July 2013, Melbourne, Australia,

8 ASAR and ASAR versus HOBE in situ Soil Moisture!! Limited number of temporal matches!!

9 Sentinel-1 A Game Changer C-band SAR satellite in continuation of ERS-1/2 and ENVISAT High spatio-temporal coverage Spatial resolution m Temporal resolution < 3 days over Europe and Canada with 2 satellites Excellent data quality Highly dynamic land surface processes can be captured Impact on water management, health and other applications could be high if the challenges in the ground segment can be overcome Solar panel and SAR antenna of Sentinel-1 launched 3 April Image was acquired by the satellite's onboard camera. ESA

10 From 150 km ASAR WS to 20 m Sentinel 1

11 Sentinel-1 Cross-Pol (VH) Images Red June Green July Blue August False-colour image of Sentinel-1 VH monthly image mosaics

12 Sentinel-1 Data Volume

13 EODC Infrastructure in Vienna Virtual Machines (VMs) Supercomputer VSC-3 Rank 85 of the World s most powerful computers (11/2014) 24/7 Operations & Rolling Archive Petabyte-Scale Disk Storage 20 Petabyte until 2018 Tape Storage

14 Sentinel-1 Data EODC Sentinel-1 data are currently available ~2,5 hours after its processing time and 6,25 hours after acquisition time (median value for August 2015) Already more than 40 TB (>1,5 times our 10-year ENVISAT ASAR archive) Ramp-up of Sentinel-1 acquisition scenario to full operational status Up-to-date coverage maps available from

15 SAR Geophysical Retrieval Toolbox (SGRT)

16 Equi7 Grid Optimised for global scale time series processing of Sentinel-1 data 7 planar, orthogonal grids for continental zones [in m] 1 python software for handling class Equi7Grid(), Equi7Tile() Bauer-Marschallinger et al (2014) Optimisation of global grids for high-resolution remote sensing data, Computers & Geosciences, 72,

17 Supercomputing Experiment Vienna Scientific Cluster 3 High-performance computing (HPC) system with 2020 nodes Each node has 2 processors Intel Xeon E5-2650v2, 2.6 GHz, and 64 Gbytes of RAM Simple Linux Utility for Resource Management (SLURM) Experiment Geocoding of 624 Sentinel-1 images from Austria, Sudan and Zambia with Sentinel-1 toolbox Each image is about 1 Gbyte in size Serial processing with one processor would take about two weeks Approach Parallel processing on 312 nodes whereas 2 images were simultaneously launched on a single computing node Results Processing was completed within 45 min (without queuing)

18 Soil Moisture Retrieval for Sentinel-1 Baseline algorithm Change detection approach as developed for ERS SCAT and METOP ASCAT and later adopted to ENVISAR ASAR Science questions Impact of VV polarisation for Sentinel-1 versus HH for ENVISAT ASAR? Value of VH polarisation for improving soil moisture retrieval? How to improve the vegetation parameterisation? Benefit from alternative modelling/retrieval approaches Theoretical backscatter models Semi-empirical models Statistical approaches Artificial Neural Networks Support Vector Regression Bayesian models

19 First 1 km Sentinel-1 Soil Moisture Images 0 % Relative Surface Soil Moisture Content 100 % Monthly SSM image mosaic for June 2015 over Austria

20 Conclusions Coarse-resolution microwave soil moisture data services are increasingly becoming mature Many users want to move to 1 km and finer Due to the loss of the SMAP radar, Sentinel-1 is currently the only microwave sensor with a suitable spatio-temporal resolution/coverage Petabyte storage and supercomputing capabilities needed Operational Sentinel-1 data processing capabilities established by EODC and its cooperation partners Validation and scientific activities are just starting major scientific advances can be expected Acknowledgements Austrian Space Application Programme: Projects Prepare4EODC and WetMon European Community's 7th Framework Programme: Grant agreement no AdvancedSAR European Commission Joint Research Centre: Framework contract Copernicus Global Land European Space Agency: Contract No /12/I-NB TIGER NET