GlobSnow Snow Water Equivalent Products

Overview

The GlobSnow project aims to create temporally and spatially extensive snow products with well-known accuracy characteristics. The snow products are based on current state of the art algorithms that can be employed for global scale snow monitoring. Two snow parameters: snow extent (SE) and snow water equivalent (SWE) are produced within GlobSnow. All versions of GlobSnow 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. For all GlobSnow products snow depth solutions are converted to snow water equivalent using a static density parameter. While GlobSnow updates have continued, parallel development of a Snow CCI SWE product has also occurred, hence there are similarities between the two suites of products.

Provider's contact information

General Information about the GlobSnow Project: http://www.globsnow.info/swe/

Key contact is Dr. Kari Luojus (firstname.lastname@fmi.fi)

Licensing

Licence: Public/None

Dataset citable as: 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.

Variable name and units:

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

Spatial coverage and resolution:

Northern Hemisphere
Products provided in Equal-Area Scalable Earth Grid (EASE-Grid) (Lambert equal-area azimuthal - projection).
The nominal resolution of single pixel is 25 km x 25 km; geometry of the pixels varies
The data field has the size of 721 x 721 (rows x columns).
Product is limited between latitudes 35⁰N and 85⁰N for physical reasons.

Temporal coverage and resolution:

1979-01-06 – 2018-05-31 (v3.0).

Three frequencies of output available:

Daily Snow Water Equivalent (Daily L3A SWE), snow water equivalent (mm) for each grid cell for all evaluated land areas of the Northern Hemisphere
Weekly Aggregated Snow Water Equivalent (Weekly L3B SWE), calculated for each day based on a 7-day sliding time window aggregation of the daily SWE product.
Monthly Aggregated Snow Water Equivalent (Monthly L3B SWE) a single product for each calendar month providing the average and maximum SWE, calculated from the weekly aggregated SWE product.
There also exists a bias-corrected monthly product available for Feb-May only. The bias corrected product uses in situ snow transects to correct SWE amounts in the monthly product at the continental scale (Pulliainen et al. 2020). Sub-continental scale biases may still exist. Corrections are considered most appropriate for March. Availability of in situ data may influence other months.

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

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

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

Information about related datasets

GlobSnow version 3.0: most current algorithm version
GlobSnow version 1.0, 1.3, 2.0, 2.1: previous versions of the product (no longer updated, available over shorter periods
GlobSnow NRT: near-real-time version constrained by low-latency selection of synoptic snow depth data
Copernicus NRT: GlobSnow SWE NRT product combined with IMS-mask and regridded to 0.05⁰ lat/lon.

Limitations and strengths for application in North Canada

In situ snow depth 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. All land ice 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

Version 3.0:

Improvements to the GlobSnow algorithm implemented for v3.0 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.

Bias-corrected version:

Pulliainen, J., K. Luojus, C. Derksen, et al. Patterns and trends of Northern Hemisphere snow mass from 1980 to 2018. Nature 581, 294–298 (2020). https://doi.org/10.1038/s41586-020-2258-0

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, B., 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:

GlobSnow Product Versions: http://www.globsnow.info/swe/ (net CDF; some versions available in HDF)

Copernicus NRT version: https://land.copernicus.eu/global/products/swe