European Space Agency (ESA) Snow Climate Change Initiative (Snow CCI)

Overview

Snow CCI data is one component of an European Space Agency (ESA) initiative to generate historical records of essential climate variables that meet the requirements of the Global Climate Observing System (GCOS). The Snow CCI project has developed both snow cover fraction products and snow water equivalent (SWE) products. SWE products are derived from multiple sensors/instruments housed on a variety of satellites (SMMR, SSM/I, and SSMIS from a sequence of DMSP F-series satellites starting in 1978 until present day); various efforts are used to ensure long-term consistency in the records. The Snow CCI SWE product algorithm advanced upon the GlobSnow SWE algorithm and hence shares similarities with GlobSnow product versions. All versions of these snow water equivalent products represent snow depth solutions optimized to fit three sources of data: observed microwave brightness temperatures, observed synoptic weather station snow depths, and modelled microwave emission characteristics related to snow grain size. Snow depth solutions are converted to snow water equivalent using either a static density parameter (Snow CCI v1.0) or a spatially and temporally varying parameter interpolated from in situ snow density data (Snow CCI v2.0). For more information please see the Snow CCI product user guide.

Provider's contact information

ESA Snow CCI Project Page: https://climate.esa.int/en/projects/snow/

ESA Snow CCI Development Team Contact: http://snow-cci.enveo.at/contact.html

Licensing

Licence: described here.

Dataset citable as: Luojus, K., M. Moisander, J. Pulliainen, M. Takala, J. Lemmetyinen, C. Derksen, C. Mortimer, G. Schwaizer, T. Nagler, 2020: ESA Snow Climate Change Initiative (Snow CCI): Snow Water Equivalent (SWE) level 3C daily global climate research data package (CRDP) (1979 – 2018), version 1.0. Centre for Environmental Data Analysis, 20 April 2020. doi:10.5285/fa20aaa2060e40cabf5fedce7a9716d0.

Variable name and units:

Snow water equivalent, snw [mm] (1 mm = 1 kg m-2)

Spatial coverage and resolution:

Northern Hemisphere
Products provided on regular lon-lat grid: 0.25⁰ x 0.25⁰ (v1.0) and 0.10⁰ x 0.10⁰ (v2.0)
Product is limited between latitudes 35⁰N and 85⁰N for physical reasons.

Temporal coverage and resolution:

1979-01-06 -- 2020-05-31. (v2.0)

1979-01-06 -- 2018-05-31. (v1.0)

For the period from 1979 to May 1987, the products are available every second day.

From October 1987 until May 2018, the products are available daily.

Products are only generated for the Northern Hemisphere winter seasons, usually from beginning of October until the middle of May.

Information about related datasets

Internal Snow CCI versions (1.1, 1.2, 1.3, 1.4, 1.5): development versions not officially released but publically available for research purposes.

GlobSnow versions 1.0, 1.3, 2.0, 2.1, 3.0, nrt: see GlobSnow document

Limitations and strengths for application in North Canada

In situ snow depth observations (and for v2.0 in situ snow density observations) are used to constrain the satellite snow depth retrievals. This information is sparser in Northern Canada such that the resulting retrievals are based on data interpolated/extrapolated from further away. The effect of this process on product uncertainty is not completely understood.

Because of known limitations in alpine terrain, a complex-terrain mask is applied based on the sub-grid variability in elevation determined from a high-resolution digital elevation model. Permanent land ice (glaciers, ice sheets) and large lakes are also masked.

Products have been shown to be less accurate in deep snow (SWE >200 mm)

References to documents describing the methodology or/and the dataset

Snow CCI:

Improvements to the GlobSnow algorithm implemented for Snow CCI version 1.0 include the utilization of an advanced emission model with an improved forest transmissivity module and treatment of sub-grid lake ice. Because of the importance of the weather station snow-depth observations on the SWE retrieval, there is improved screening for consistency through the time series. Snow CCI v2.0 will include a spatially and temporally varying snow density (Venäläinen et al., 2021) to convert snow depth to SWE and will use an updated satellite data time series.

Venäläinen, P., K. Luojus, J. Lemmetyinen, J. Pulliainen, M. Moisander, and M. Takala, 2021: Impact of dynamic snow density on GlobSnow snow water equivalent retrieval accuracy, The Cryosphere, 15(6), https://doi.org/10.5194/tc-15-2969-2021

Original GlobSnow algorithm:

General description at: https://www.globsnow.info/index.php?page=Snow_Water_Equivalent

Pulliainen, J., J. Grandell, and M. T. Hallikainen, 1999: HUT Snow Emission Model and its Applicability to Snow Water Equivalent Retrieval. IEEE Transactions on Geoscience and Remote Sensing. 37: 1378-1390.

Pulliainen, J., 2006: Mapping of snow water equivalent and snow depth in boreal and sub-arctic zones by assimilating space-borne microwave radiometer data and ground-based observations. Remote Sensing of Environment. 101: 257-269. DOI: 10.1016/j.rse.2006.01.002.

Takala, O. M., J. Pulliainen, S. Metsämäki, and J. Koskinen, 2009: Detection of snowmelt using spaceborne microwave radiometer data in Eurasia From 1979 to 2007. IEEE Transactions on Geoscience and Remote Sensing, 47, 2996-3007.

Takala, M., K. Luojus, J. Pulliainen, C. Derksen, J. Lemmetyinen, J.-P. Kärnä, J. Koskinen, B. Bojkov, 2011: Estimating northern hemisphere snow water equivalent for climate research through assimilation of spaceborne radiometer data and ground-based measurements, Remote Sensing of Environment, Vol. 115, Issue 12, 15 December 2011, doi: 10.1016/j.rse.2011.08.014.

Link to download the data and format of data:

https://climate.esa.int/en/odp/#/project/snow (multiple snow variables available)

http://dx.doi.org/10.5285/fa20aaa2060e40cabf5fedce7a9716d0 (SWE v1.0, netcdf)

http://dx.doi.org/10.5285/4647cc9ad3c044439d6c643208d3c494 (SWE v2.0)