Arctic Soil Freeze/Thaw Status from SMMR and SSM/I, Version 2

Summary

This data set contains near-surface (< 5 cm) soil freeze/thaw status on snow-free and snow-covered land surfaces over the Arctic terrestrial drainage basin. The near-surface soil freeze/thaw status is determined by using passive-microwave remote sensing data over snow-free land and a numerical model over snow-covered land. Data are projected to a 25 km x 25 km Northern Hemisphere EASE-Grid. Version 2 of this data set greatly extends the temporal coverage and makes use of data from SMMR as well as SSM/I. Data are from October 1978 to June 2004. Data are in ASCII text format and are available via FTP.

Citing These Data:

Zhang, T. and R. Armstrong. 2003 updated 2005. Arctic Soil Freeze/Thaw Status from SMMR and SSM/I, Version 2. Boulder, CO: National Snow and Ice Data Center. Digital Media.

Overview Table

Category	Description
Data format	Data are in ASCII text format, compressed with gzip.
Spatial coverage and resolution	This data set covers the Arctic terrestrial drainage basin at 25-km resolution.
Temporal coverage and resolution	Data are grouped by month from October 1978 through June 2004. Each file contains daily data values.
Grid type and size	Data are gridded to the Northern Hemisphere EASE-Grid projection.
File naming convention	ggd641_freezethaw_arctic.yyyy.mm.txt
File size	One 148.3 MB tarred and compressed file contains 309 individual 10.3 MB files.
Parameter(s)	Data contain latitude, longitude, and near-surface freeze/thaw status.
Procedures for obtaining data	Data are available via FTP.

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments:

Investigator(s) Name and Title:

Tingjun Zhang and Richard Armstrong
National Snow and Ice Data Center

Technical Contact:

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

2. Detailed Data Description:

Format:

Data are in ASCII text format, compressed with gzip. Three hundred nine files contain data from October 1998 through June 2004. Each file contains columns for latitude, longitude, and surface type for each day of the month. A two line header indicates the column headers, the year and month, and a key to the values for the surface types. Surface type values are as follows:

1: Snow-free, unfrozen ground
2: Snow-free, frozen ground
3: Snow-covered, unfrozen ground
4: Snow-covered, frozen ground
5: Desert (south of 50°N)
6: Mixed land and ocean
7: Lake or ocean

File Naming Convention:

The file-naming convention is "ggd641_freezethaw_arctic.yyyy.mm.txt."

File Size:

One 148.3 MB tarred and compressed file contains 309 individual 10.3 MB files.

Spatial Coverage:

This data set covers the entire Arctic terrestrial drainage basin. This area includes land with ice or water that empty into the Arctic Ocean, Hudson Bay, James Bay, Hudson Strait, and the Bering Sea. The Arctic drainage basin spans overs regions of seasonally-frozen ground in the south, to permafrost regions in the north. Continuous permafrost underlies nearly half of the Arctic drainage basin (Brown et al. 1998, Zhang et al. 2000).

Spatial Coverage Map:

The following image from 02 January 1999 was created from "Arctic Soil Freeze/Thaw Status from SMMR and SSM/I, Version 2" data. It shows the spatial extent of the Arctic terrestrial drainage basin. Click on the thumbnail to see a larger image.

Spatial Resolution:

Spatial resolution is 25 km.

Grid Description:

Input data are interpolated to a spatial subset of the Northern Hemisphere EASE-Grid projection that represents the Arctic drainage basin. (See All About EASE-Grid for further details.) Data are output to ASCII text format.

Temporal Coverage:

Data are grouped by month from October 1978 through June 2004. Each file contains daily data values.

Sample Data Record:

Each data file consists of a two-line header followed by columns for latitude, longitude, and surface type for each day of the month. Missing data, or when days 29, 30 and 31 do not exist, are indicated by values of "-9999.0." Following are the first two data records in a sample file called "ggd641_freezethaw_arctic.1998.08.txt":


1998 08 SSM/I Freeze/Thaw  1: unfrozen bare ground  2: frozen bare ground  3: unfrozen snow-covered ground  4: frozen snow_covered ground  5: desert (south of 50N)  6: mixed land/ocean  7: lake/ocean
"CellID"  "Lat"   "Long"   "01"    "02"    "03"    "04"    "05"    "06"    "07"    "08"    "09"    "10"    "11"    "12"    "13"    "14"    "15"    "16"    "17"    "18"    "19"    "20"    "21"    "22"    "23"    "24"    "25"    "26"    "27"    "28"    "29"    "30"    "31"  
     1  56.5398 201.6560       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6
     2  56.6259 201.2912       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6       6

3. Data Access

Data Access:

Data are available via FTP.

Related Data Collections:

Please visit the Frozen Ground Data Center site at NSIDC for a complete listing of data sets.

4. Data Acquisition and Processing:

Data Source:

Zhang and Armstrong obtained input data from the following sources:

Passive-microwave T_Bs
This study uses 18-Ghz and 37-Ghz T_Bs from the Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures and the 19-GHz and 37-GHz T_Bs from the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures data set, available from NSIDC.

Air Temperature
The National Water and Climate Center (NWCC), Natural Resources Conservation Center (NRCC) of the U.S. Department of Agrictulture provided mean daily and monthly air temperature data. The University of Delaware's Center for Climate Research provided gridded mean monthly air temperatures over the study area. The 0.5° x 0.5° gridded latitude/longitude data were gridded into the 25-km EASE-Grid. Mean daily air temperature was derived from the mean annual air temperature and annual amplitude, which were derived from mean monthly air temperature.

Snow Cover
Zhang and Armstrong calculated snow water equivalent from the Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures and DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures data sets, available from NSIDC. The Chang (1987) algorithm, originally used for calculating snow water equivalent from Scanning Multichannel Microwave Radiometer (SMMR) passive-microwave data from 1978 to 1987, was modified for the SSM/I data.

Soil Temperature
The National Water and Climate Center (NWCC), Natural Resources Conservation Center (NRCC) of the U.S. Department of Agrictulture provided hourly soil temperature data at depths of 0 cm, 5 cm, 10 cm, 20 cm, 40 cm, 80 cm, 100 cm, and 150 cm. Ground surface temperature is measured only at a few selected sites. This study uses soil temperature data at 5-cm depth from all sites.

Derivation Techniques and Algorithms:

This data set is derived from a frozen-soil algorithm that combines passive-microwave remote sensing and numerical modeling methods. The first step is to compile the input data described in the Data Source section of this document. Using available ground-based and satellite data, Zhang and Armstrong determine where snow exists over the study area. Over snow-free land, they use a frozen-soil algorithm using SMMR and SSM/I data to detect near-surface freeze/thaw status. Over snow-covered land areas, they use a one-dimensional heat transfer numerical model with phase change to detect soil freeze/thaw status.

Passive-microwave algorithm
SSM/I 19-GHz and 37-GHz vertically-polarized T_Bs discriminate frozen ground from unfrozen ground over prairie soils, using the following equation:

(T_B(37V) - T_B(19V))/18 < 0

and

T_B(37V) < 258.2 K

A similar approach is used with the SMMR data using the 18-Ghz and 37-Ghz channels.

Mixed land and water pixels provide misleading information on the land surface freeze and thaw status; therefore, areas up to approximately 50 km from the coasts of large water bodies are masked out.

Numerical model
This study uses a numerical model for one-dimensional heat transfer with phase change to simulate the soil freezing and thawing processes with or without snow cover. This model has shown excellent previous results for active-layer depth and soil temperatures when driven by well-known boundary conditions and forcing parameters at specific locations (Zhang, Osterkamp, and Stamnes 1996).

5. References and Related Publications:

Armstrong , R.L., and M.J. Brodzik. 2002. Northern Hemisphere EASE-Grid weekly snow cover and sea ice extent, Version 2. Boulder, CO: National Snow and Ice Data Center. CD-ROM.

Brodzik, M.J. 1997. EASE-Grid: A versatile set of equal-area projections and grids. Boulder, CO, USA: National Snow and Ice Data Center.

Brown, J., O.J. Ferrians, Jr., J.A. Heginbottom, and E.S. Melnikov. 1998. Digital Circum-Arctic map of permafrost and ground-ice conditions. In International Permafrost Association, Data and Information Working Group, comp. Circumpolar Active-Layer Permafrost System (CAPS), version 1.0. Boulder, CO: National Snow and Ice Data Center. CD-ROM.

Chang, A.T.C., J.L. Foster, and D.K. Hall. 1987. Nimbus-7 SMMR derived global snow cover parameters. Annals of Glaciology 9:39-44.

Global Soil Data Task. 2000. Global gridded surfaces of selected soil characteristics. International Geosphere-Biosphere Programme - Data and Information Services (IGBP-DIS). Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center. Available online at http://www.daac.ornl.gov.

Goodrich, L.E. 1982. Efficient numerical technique for one-dimensional thermal problems with phase change. International Journal of Heat and Mass Transfer 21:615-621.

Holden, J.B., C.J. Vörösmarty, S. Frolking, and R. Lammers. 2001. A large-scale water balance model for permafrost terrain. Arctic and Alpine Research. In press.

Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J. Woolen, Y. Zhu, M. Chelliah, W. Ebisuzaki, W. Higgens, J. Janowiak, K.C. Mo, C. Ropelewski, J. Wang, A. Leetma, R. Reynolds, R. Jenne, and D. Joseph. 1996. The NCEP/NCAR 40-year reanalysis project. Bulletin of the American Meteorological Society 77:437-471.

Meteorological Service of Canada (MSC). 2000. Canadian Snow Data CD-ROM. Downsview, Ontario, Canada: Meteorological Service of Canada, CRYSYS Project, Climate Processes and Earth Observation Division.

Oelke, C., T. Zhang, M. Serreze, and R. Armstrong. 2003. Regional-scale modeling of soil freeze/thaw over the Arctic Drainage Basin. Journal of Geophysical Research-Atmospheres 108(D10) (May).

Sturm, M., J. Holmgren, and G.E. Liston. 1995. A seasonal snow cover classification system for local to global applications. Journal of Climate 8:1261-1283.

Zhang, T., and R.L. Armstrong. 2001. Soil freeze/thaw cycles over snow-free land detected by passive microwave remote sensing. Geophysical Research Letters 28(5): 763-766.

Zhang, T., J.A. Heginbottom, R.G. Barry, and J. Brown. 2000. Further statistics on the distribution of permafrost and ground-ice in the Northern Hemisphere. Polar Geography 24(2):126-131.

Zhang, T., R.G. Barry, K. Knowles, J.A. Heginbottom, and J. Brown. 1999. Statistics and characteristics of permafrost and ground ice distribution in the Northern Hemisphere. Polar Geography 23(2):147-169.

Zhang, T., T.E. Osterkamp, and K. Stamnes. 1996. Influence of the depth hoar layer of the seasonal snow cover on the ground thermal regime. Water Resources Research 32(7):2075-2086.

6. Document Information:

List of Acronyms

The following acronyms are used in this document:

ASCII: American Standard Code for Information Interchange
EASE-Grid: Equal-Area Scalable Earth Grid
FTP: file transfer protocol
NRCC: National Resources Conservation Center
NWCC: National Water and Climate Center
SMMR: Scanning Multichannel Microwave Radiometer
SSM/I: Special Sensor Microwave/Imager

Service Interruption

National Snow and Ice Data Center