This document summarizes recent developments in improving satellite-derived snow depth products from AMSR-E measurements. It outlines issues with radio frequency interference (RFI), lake signals, and forest attenuation that negatively impact the current product. The performance of the current satellite-only product is described, along with development areas to better account for RFI, lakes, and forests through approaches like removing the 10 GHz channel in RFI areas, correcting for lake ice thickness effects, and improved transmissivity corrections. There is potential to implement these developments operationally and to consider moving to a higher resolution grid than the current 25 km given the sensor capabilities.

1. Improving the AMSR-E snow depth product: recent developments Richard Kelly University of Waterloo, Canada.

2. Outline Current product: performance of the satellite only product Development issues RFI Lake behaviour Forest attenuation Observations and Conclusions

3. Current snow depth product: Approach (AMSR-E observation-based) where fd=50% ff=40% r=12.5km fd=10% ff=40% IFOV radius=12.5 km Forest stand

4. Performance (2002-2003)

5. comments Retrievals are conducted at the IFOV level (not at the grid-averaged level) Retrievals are then aggregated to coarser grid (0.25x025 deg) Tb correction (forest only) is built into the retrievals but not perfectly formulated. RFI and water bodies not well accounted for.

6. RFI issues

7. RFI Kidd, C.(2006) 'Radio frequency interference at passive microwave earth observation frequencies’, International Journal of Remote Sensing,27:18,3853 — 3865

8. RFI impacts MODIS-Daily 2 Feb. 2009 3 Feb. 2009 4 Feb. 2009 5 Feb. 2009 6 Feb. 2009 7 Feb. 2009 8 Feb. 2009 9 Feb. 2009 10 Feb. 2009 From sat.dundee.ac.uk

9. RFI impacts UK AMSR-E Daily Snow 2.2.2009 Missing / bad Water 320 – 540 160 - 320 80 - 160 40-80 1 - 40 0 SWE [mm]

10. RFI impacts 10V-36V (current) 10V GHz 5 February 2009

11. Adjusted retrievals without the use of the 10 GHz channel in UK.

12. Lake issues

13. Much of the Arctic and sub-Arctic are dominated by lake cover (fractions of 40% not uncommon). At 25 km grid resolution lakes will play an important role But what is that role and can lake signals be identified? Time series of data for 9 years.

14. Kang et al. (2010) GRSL 7(4)

15. A note on gridding and AMSR-E measurement samples Depending on the proximity threshold (x), may or may not be daily, but it will be for a consistent location 10 km 25 km LOI x 10 km AMSR-E sampling grid

16. MOD44W Water mask & MODIS VCF 25 km diameter circle averaged on 1 km grid 25km Water Fraction 0-10% 11-20% 21-30% 31-50% >50% Forest Fraction 0% 1-10% 11-20% 21-30% 31-50% >50% 0 400 km

17. AMSR snow depth (0.25x0.25 deggridded) Snow depth (cm) Date

18. Nearest WMO snow depth / air temperature 0% FF & 37% WF Mean Temp (C) Snow depth (cm) 0% FF & 35% WF Date

19. AMSR Tbs (36V & 18V): centre within 4 km of locations of interest Tb (K) Date

20. AMSR Tbs (36V & 18V) Lake freeze-up Snow and lake ice melt Snow accumulation on lake

21. Forest fraction

22. MOD44W Water mask & MODIS VCF 25 km diameter circle averaged on 1 km grid Water Fraction 0-10% 11-20% 21-30% 31-50% >50% Forest Fraction 0% 1-10% 11-20% 21-30% 31-50% >50% 0 400 km

23. AMSR snow depth (0.25x0.25 deg gridded) Snow depth (cm) Date

24. AMSR Tbs (36V & 18V): centre within 4 km of locations of interest Tb (K) Date

25. Forest & lakes combined

26. And when you mix forest and lakes…. MOD44W Water mask & MODIS VCF 25 km diameter circle averaged on 1 km grid Water Fraction 0-10% 11-20% 21-30% 31-50% >50% Forest Fraction 0% 1-10% 11-20% 21-30% 31-50% >50% 0 400 km

27. AMSR snow depth (0.25x0.25 deg gridded) Snow depth (cm) Date

28. 4% Water fraction and 55% forest fraction

29. AMSR Tbs (36V & 18V): centre within 4 km of locations of interest Tb (K) Date

30. Areas of development RFI can be accommodated in the current implementation by a of 10 GHz observations with 18 GHz in the affected areas Water fraction changes the nature of a Tb difference or ratio. 18 GHz is sensitive to lake ice thickness so that DTb is not necessarily a function of DSD or SWE. Forest fraction/structure reduces sensitivity (known). But it is likely not a linear forest fraction attenuation effect Forest and water fraction together require correction before SWE inversion is applied. Recent work by Langloiset al. (2011) has demonstrated new approach to transmissivity correction and lake fraction can likely be corrected for (ongoing work) Operational implementation of forest and lake correction is yet to be completed.

31. Is it not time we began looking at grids that are higher resolution – 25 km EASE grid was chosen because the SSM/I 37 GHz approximate this resolution? AMSR-E/GCOM-W are at 10x14 km at 36 GHz. Perhaps a higher spatial resolution (e.g. 12.5km grid)? Thank you