PROGRESS IN ADDRESSING SCIENCE GOALS FOR SNOW MONITORING BY MEANS OF SAR

Transcription

1 Polar Space Task Group PROGRESS IN ADDRESSING SCIENCE GOALS FOR SNOW MONITORING BY MEANS OF SAR Thomas Nagler, Helmut Rott, ENVEO IT GmbH, Innsbruck, Austria

2 SNOW: Observational Requirements and SAR Products Observational requirements for satellite-based snow extent products for operational hydrology and climate research (IGOS Cryosphere Theme Report): Spatial resolution: 100 m Revisit time: 1 day Product type of the current satellite-based C-band SAR Systems: Extent of snow melt area based on backscatter sensitivity to wet snow C-band SAR is not suitable for operational monitoring of dry snow areas very limited sensitivity to dry snow. PSTG 5 th Session, 5-7 Oct Nagler & Rott 2

3 SAR Concept for Retrieval of Snowmelt Area Exploits the contrast of backscatter (σ ) between wet snow and snowfree surfaces (reduced σ of wet snow) Applies the backscatter ratio (σ wet snow / σ snow-free ) to compensate for topographic effects (local incidence angle) Applies a segmentation procedure to separate the two surface types in σ ratio images σ varies with incidence angle θ and polarization: σ (VV) decreases for lower θi Noise floor (NESZ) may be problem for σ (VH) at high θi Solution: Apply weighting function W(θi) for fusion of σ (VV) and σ (VH) Based on in-situ Scat data, Leutasch, Austria PSTG 5 th Session, 5-7 Oct Nagler & Rott 3

4 Retrieval of Snowmelt Area by S1 IW Mode Data Flowline for Retrieval algorithm from Sentinel-1 IW-mode data (SLC) SLC data enable optimal speckle filtering, data fusion, segmentation and geocoding σ ratio in IW mode data, for area in Eastern Alps, 2 June 2015 σ (VV) σ (VH) PSTG 5 th Session, 5-7 Oct Nagler & Rott 4

5 Sentinel-1 Maps of Snow melt Area, April and May April & Track : 20.Apr 088: 21.Apr 095: 22.Apr 117: 23.Apr Track : 14.May 088: 15.May 095: 16 May 117: 17 May PSTG 5 th Session, 5-7 Oct Nagler & Rott 5

6 Comparison MODIS Snow Extent / S1 Snowmelt Area MODIS, May 2015, Map of Fractional Snow Extent (grid size 250 m) Confusion Matrix S1 MODIS S1 Snow Melt Area 2015/05/ m grid Confusion Matrix Probability σ for snow/snowfree areas from MoDIS PSTG 5 th Session, 5-7 Oct Nagler & Rott 6

7 Sentinel-3

8 Prototpye Algorithm for Sentinel-3 Snow Mapping S3 Algorithm developed and tested with AATSR and MERIS of Envisat Fractional Snow Extent applying Multi-spectral Algorithm PSTG 5 th Session, 5-7 Oct Nagler & Rott 8 Thomas Nagler

9 FSC MERIS AATSR + AATSR 1000 m 300 m 15 km 10 April 2003 PSTG 5 th Session, 5-7 Oct Nagler & Rott 9

10 Conclusion The Sentinel-1 satellite formation offers excellent capabilities for operational monitoring of snow melt area at high spatial resolution. The Interferometric Wide swath (IW) mode data provide 4 to 6 day revisit capability at mid-latitudes, improving to 2 to 3 days after deployment of the 2 nd satellite. Daily revisit will be feasible at high latitudes. A prototype algorithm for retrieval of snowmelt area has been developed, applying the fusion of co- and cross-polarized channels to optimize the discrimination of snow vs. snow-free areas over a wide range of incidence angles. SSC-mode data as input for the retrieval provide the full backscatter signal statistics and geometric resolution, enabling optimum exploitation of sensor capabilities for speckle filtering, channel fusion, segmentation, and rectification. Further testing and validation of the snow product and algorithm is recommended, in order to assess the performance in different snow regions. Systematic S1 acquisition of mountain regions especially during melting period needed. PSTG 5 th Session, 5-7 Oct Nagler & Rott 10