MEaSUREs Global Record of Daily Landscape Freeze/Thaw Status

Summary

Platform:	Defense Meteorological Satellite Program (DMSP) satellite series
Sensor:	Special Sensor Microwave Imager (SSM/I)
Parameters:	Landscape AM Freeze/Thaw (FT) State of Water Landscape PM Freeze/Thaw State of Water Landscape Combined Freeze/Thaw State of Water Landscape Transitional Freeze/Thaw State of Water Landscape Inverse Transitional Freeze/Thaw State of Water Annual Quality Assurance (QA) Metric of FT Classification Accuracy Annual and Daily Accuracy Metrics of FT Classification Results
Spatial Coverage:	Global
Temporal Resolution:	Daily Morning Overpass (AM) Daily Afternoon Overpass (PM) Daily Combined (CO)
Project:	NASA MEaSUREs (Making Earth System Data Records for Use in Research Environments) program
Temporal Coverage:	01 January 1988 to 31 December 2007
Format:	HDF5, PNG, GIF
Version History:	Version 2 was released 7 January 2013. Please see the Version 2 documentation to obtain the most recent data.

Note: These data are considered provisional pending a review by the MEaSUREs program. Once the data have been reviewed, this statement will be removed from this documentation.

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title and version number, dates of the data you used (for example, December 2003 to March 2004), publisher: NSIDC, and digital media.

Kim, Youngwook, John Kimball, and Kyle McDonald. 2010. MEaSUREs Global Record of Daily Landscape Freeze/Thaw Status, Version 01, [list the dates of the data used]. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	HDF5 PNG images GIF animations
Spatial coverage and resolution	Southernmost Latitude: 84.240° S Northernmost Latitude: 86.717° N Westernmost Longitude: 179.999° W Easternmost Longitude: 179.740° E The spatial resolution is 25 km
Temporal coverage and resolution	Temporal Coverage 01 January 1988 to 31 December 2007 Temporal Resolution Daily Morning Overpass (AM) Daily Afternoon Overpass (PM) Daily Combined (CO)
Tools for accessing data	HDF5: HDF5 compatible applications such as HDFView or Panoply PNG and GIF: Web browsers and graphics applications
Grid/projection description	Each FT file is projected in a global EASE-Grid
File naming convention	[Instrument]_[Channel][Polarization]_[OverpassCode]_FT_[Year]_day[DOY].h5 FT_global_1988-2007_[Metric].h5 [Instrument]_[Channel][Polarization]_[OverpassCode]_FT_[Year]_day[DOY].png FT_[OverpassCode]_[Period]_[Year].gif
File size	File sizes range from .19 MB to 12 MB for a total volume of 6.1 GB
Parameter(s)	Landscape AM Freeze/Thaw (FT) State of Water Landscape PM Freeze/Thaw State of Water Landscape Combined Freeze/Thaw State of Water Landscape Transitional Freeze/Thaw State of Water Landscape Inverse Transitional Freeze/Thaw State of Water Annual Quality Assurance (QA) Metric of FT Classification Accuracy Annual and Daily Accuracy Metrics of FT Classification Results
Procedures for obtaining data	Version 2 was released 7 January 2013. Please see the Version 2 documentation to obtain the most recent data.

Table of Contents

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

Dr. John Kimball, PI
Numerical Terradynamic Simulation Group (NTSG)
The University of Montana
Missoula, MT 59812

Dr. Youngwook Kim, Science Lead
Numerical Terradynamic Simulation Group (NTSG)
The University of Montana
Missoula, MT 59812

Joe Glassy, Software and Data Management Lead
Numerical Terradynamic Simulation Group (NTSG)
The University of Montana
Missoula, MT 59812

Dr. Kyle McDonald, Co-PI
Jet Propulsion Laboratory (JPL)
California Institute of Technology
Pasadena, CA 91109

Technical Contact

Acknowledgements

These data were generated through a grant from the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program. Portions of this work were conducted at the University of Montana and Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.

2. Detailed Data Description

Format

HDF5

This data set consists of the following three types of data stored in HDF5 v1.8.4 format:

• The daily freeze/thaw (FT) classification status
• Quality assurance (QA) data characterizing the quality of the primary FT data on an annual basis
• Accuracy metrics defined from daily FT validations against in situ daily surface air temperature observations from the World Meteorological Organization (WMO) weather stations and expressed as annual (percent) accuracy images

The cell_lat and cell_lon fields appearing in the HDF5 files are included for CF v1.4 compliance allowing users of common free software packages, such as HDFView and Panoply, to immediately view the data sets projected in a global geographic grid.

FT Classification

Each HDF5 v1.8.4 file contains the following data fields:

Field	Description	Dimension	Data Type
FT_SSMI	FT status derived from SSM/I	1383 columns; 586 rows	8-bit unsigned integer
cell_lat	Latitude	1383 columns; 586 rows	32-bit floating point
cell_lon	Longitude	1383 columns; 586 rows	32-bit floating point

The metadata for the AM and PM HDF5 files includes an aggregate daily accuracy metric (Accuracy_Daily_Metric).

FT Quality Assurance

Annual QA maps are stored in a single HDF5 v1.8.4 file, with one data field per year, for years 1988 through 2007. The QA data values are stored as single precision real (32 bit) variables, in a qualitative and dimensionless value range {0.0 <= QA <= 1.0} indicating estimated poor (0) to best (1) data quality on a grid cell-wise basis. The QA data do not vary by AM, PM, or CO (AM & PM) overpass retrievals and represent a relative index of data quality derived from ancillary terrain and land cover heterogeneity information, satellite data gaps, and daily FT accuracy assessments (see Kim et al. 2011 for details).

The QA HDF5 file (FT_global_1988-2007_QA.h5) contains the following data fields:

Field	Description	Dimension	Data Type
QA_FT_ [Year]	QA	1383 columns; 586 rows	32-bit floating point
cell_lat	Latitude	1383 columns; 586 rows	32-bit floating point
cell_lon	Longitude	1383 columns; 586 rows	32-bit floating point

FT Accuracy

Freeze/Thaw accuracy data are also stored in a single HDF5 file, one data field per year, for years 1988 through 2007. The FT product accuracy is assessed on a daily basis through grid cell-to-point comparisons with daily maximum (Tmx) and minimum (Tmn) air temperature measurements from ca 3700 global WMO weather stations (see Kim et al. 2011 for details), and is distinguished on the basis of the origin data's overpass (AM or PM). Accuracy data for years 1988 through 2007 is further distinguished by overpass (AM or PM) and is included in image form in a single accuracy HDF5 file. The FT classification accuracy is defined at each in situ weather station location and expressed as a proportion (percent) of daily FT retrievals per year that are consistent with in situ air temperature measurements of FT conditions. Accuracy (percent) values are stored as single precision real (32 bit) variables, in the range {0.0 <= a <= 100.0}.

The accuracy HDF5 file (FT_global_1988-2007_accuracy.h5) contains the following data fields:

Field	Description	Dimension	Data Type
Accuracy_FT_[OverpassCode]_[Year]	FT accuracy values	1383 columns; 586 rows	32-bit floating point
cell_lat	Latitude	1383 columns; 586 rows	32-bit floating point
cell_lon	Longitude	1383 columns; 586 rows	32-bit floating point

PNG

Daily browse images of combined (CO) measurements are provided as PNGs. This is a 20-year record of global daily images that can be used for quick visual evaluation.

GIF

Animations are provided as full size (1383x586x24 bit) animated GIF streams, playable within any common Web browser such as FireFox or Microsoft IE. The images come with continental and country boundaries overlaid for easier referencing while viewing. Each animation frame contains a metadata panel at the top and a frame-sequence index along the bottom of the frame, allowing the viewer to see what day throughout the year a given frame corresponds to. The animations are structured to provide seven-day temporal resolutions throughout a given year and provide a quick temporal visualization of the FT Earth System Data Record (FT-ESDR). (Kim et al. 2011)

File and Directory Structure

Table 1 contains the descriptions of the main FTP directories. Refer to Software and Tools for more information on how to view the data.

Table 1. Directory Description

Directory	Description
ANIMATIONS	Contains daily, monthly, and weekly GIF animations of the daily FT record
DAILY_BROWSE	Contains daily browse PNG images of CO measurements
DAILY_FT	Contains AM, PM, and CO FT measurements in individual HDF5 files, as well as a tab-delimited text file containing corresponding md5 checksums
QA_ACCURACY	Contains annual QA maps and accuracy metrics in separate HDF5 files

File Naming Convention

FT data files follow these file naming conventions:

File Type	File Naming Convention
Animations	FT_[OverpassCode]_[Period]_[Year].gif Example: FT_CO_Daily_1989.gif
Daily Browse Images	[Instrument]_[Channel][Polarization]_[OverpassCode]_FT_[Year]_day[DOY].png Example: SSMI_37V_CO_FT_1988_day001.png
Daily FT	[Instrument]_[Channel][Polarization]_[OverpassCode]_FT_[Year]_day[DOY].h5 Example: SSMI_37V_AM_FT_1988_day001.h5
QA and Accuracy	FT_global_1988-2007_[Metric].h5 Example: FT_global_1988-2007_QA.h5

File Size

File sizes range from .19 MB to 12 MB for a total volume of 6.1 GB

Spatial Coverage

The spatial coverage is global:

Southernmost Latitude: -84.240° S
Northernmost Latitude: 86.717° N
Westernmost Longitude: -179.999° W
Easternmost Longitude: 179.740° E

Spatial Resolution

The spatial resolution is 25 km.

Projection and Grid Description

Each FT file is projected in a global EASE-Grid.

Temporal Coverage

The temporal coverage of this data set is from 01 January 1988 to 31 December 2007.

Temporal Resolution

Each daily FT record consists of three separate files that represent the morning overpass (AM), the afternoon overpass (PM), and a combined file (CO) that includes morning and afternoon passes.

Parameter or Variable

Parameter Description

This data set presents the predominant daily frozen and non-frozen states of the landscape for AM and PM conditions and combined (CO) daily (AM and PM) conditions. The CO daily classification results include additional discrimination of transitional (AM frozen, PM thawed), and inverse transitional (AM thawed, PM frozen) conditions. The landscape is defined as the predominant (frozen or thawed) conditions within the satellite field-of-view (FOV) and does not distinguish between surface soil, snow or vegetation elements within the FOV (see Kim et al. 2011 for details).

Landscape AM Freeze/Thaw

The AM FT variable is the predominant freeze/thaw state (solid or liquid) of water within the landscape for the satellite morning overpass.

Landscape PM Freeze/Thaw

The PM FT variable is the predominant freeze/thaw state (solid or liquid) of water within the landscape for the satellite afternoon overpass.

Landscape Combined Freeze/Thaw

The combined FT variable is the predominant frozen or thawed status of the morning (AM) and afternoon (PM) overpasses.

Landscape Transitional Freeze/Thaw

The transitional FT variable represents AM frozen and PM thawed states of the landscape as defined from respective satellite AM and PM overpasses.

Landscape Inverse Transitional Freeze/Thaw

The inverse transitional FT variable represents AM thawed and PM frozen states of the landscape as defined from respective satellite AM and PM overpasses.

Annual QA Metric of FT Classification Accuracy

Quality assurance data characterizing the quality of the primary FT data on an annual basis.

Annual and Daily Accuracy Metrics of FT Classification Results

Accuracy metrics defined from daily FT validations against in situ daily surface air temperature observations from World Meteorological Organization (WMO) weather stations and expressed as annual (percent) accuracy images.

Parameter Range

FT Classification

Table 2 describes the data classification values for the FT HDF5 files and images.

Table 2. Classification Data Values

Classification		Browse Image Color Table
	Value	R	G	B
Frozen (AM/PM frozen)	0	000	000	255
Thawed (AM/PM thawed)	1	255	000	000
Transitional (AM frozen and PM thawed)	2	168	168	000
Inverse Transitional (PM frozen and AM thawed)	3	076	230	000
Masked (permanent ice, non-vegetated, and urban area)	254	255	255	255
100 percent open water	255	255	255	255

FT Quality Assurance

The QA data values are stored in a qualitative and dimensionless value range {0.0 <= QA <= 1.0} indicating estimated poor (0) to best (1) data quality on a grid cell-wise basis. Missing values are indicated by -9999.

FT Accuracy

Accuracy (percent) values are stored in the range {0.0 <= a <= 100.0}. Missing values are indicated by -9999.

Sample Image

Figure 1. Daily Combined SSM/I FT Classification Results for 9 April 2004 Where Areas in White are Outside of the FT-ESDR Domain.

3. Data Access and Tools

Data Access

Data are available via FTP. Version 2 of this data set was released 7 January 2013. Please see the Version 2 documentation to obtain the most recent data.

Volume

The entire data set is approximately 6.1 GB.

Software and Tools

To view FT HDF5 data files use HDF5-compatible applications such as HDFView or Panoply. To view the PNG browse images or the GIF animations use Web browsers or graphics applications.

4. Data Acquisition and Processing

Theory of Measurements

This data set contains a global data record of daily landscape FT status derived from satellite microwave remote sensing. The FT state parameter derived from satellite microwave remote sensing quantifies the predominant frozen or non-frozen state of the landscape and is closely linked to surface energy budget and hydrologic activity, seasonal dynamics of vegetation growth, terrestrial carbon budgets, and land-atmosphere trace gas exchange. Satellite microwave remote sensing is well suited for global FT monitoring due to its relative insensitivity to atmospheric contamination, its independence from solar illumination, and its strong sensitivity to changes in landscape dielectric properties between frozen and thawed conditions. This Freeze/Thaw - Earth System Data Record (FT-ESDR) is derived using daily radiometric brightness temperature measurement time series at 37 GHz (V-pol) frequency from the Special Sensor Microwave Imager (SSM/I) on board the DMSP polar orbiting satellite series. The resulting FT-ESDR represents a consistent, daily FT global record that extends from 1988 to 2007 and is intended for quantifying FT state dynamics over vegetated land areas within a global domain where seasonally frozen temperatures are a major constraint to ecological processes. A detailed description of the FT-ESDR product, methods development, and validation scheme is provided by Kim et al. 2011.

Data Source

Daily, vertically polarized brightness temperatures at 37 GHz from the Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures were used as input to derive the FT-ESDR.

Derivation Techniques and Algorithms

The FT classification algorithm involves a seasonal threshold approach with radiometric brightness temperature time-series that identify FT transition sequences by exploiting the dynamic temporal response of radiometric brightness to differences in the aggregate landscape dielectric constant that occur as the landscape transitions between predominantly frozen and non-frozen conditions. These techniques are well suited for resolving daily FT state dynamics rather than single events or seasonally dominant transitions. (Kim et al. 2011)

The FT-ESDR is intended to have sufficient accuracy, resolution, and coverage to resolve physical processes linking Earth's water, energy, and carbon cycles. The product is designed to determine the FT status of the composite landscape vegetation-snow-soil medium to a sufficient level to characterize low-temperature constraints to surface water mobility, vegetation productivity, ecosystem respiration, and land-atmosphere CO2 fluxes. The FT-ESDR involves a daily binary FT state classification on a grid cell-by-cell basis, posted to a regular Earth grid. The FT classification algorithm uses a temporal change detection of radiometric brightness temperature time-series that identify FT transition sequences by exploiting the dynamic temporal brightness temperature response to differences in the aggregate landscape dielectric constant that occur as the landscape transitions between predominantly frozen and non-frozen conditions (McDonald and Kimball 2005).

Satellite ascending and descending orbital data time series are processed separately to produce information on AM, PM, and composite daily FT conditions. Additional variables distinguished by the FT-ESDR include transitional (AM frozen and PM thawed) or inverse transitional (AM thawed and PM frozen) conditions. Related variables produced from the baseline daily FT time series include the timing (Day of Year) of primary seasonal thaw and freeze events and duration (days) of frozen and non-frozen periods on an annual basis. The global FT-ESDR domain encompasses unmasked vegetated land areas where low temperatures are a significant constraint to annual vegetation productivity as defined from climatological reanalysis data. Masked areas include permanent ice and snow, barren land, open water, and regions unconstrained by freezing temperatures. The FT-ESDR map projection is defined in terms of a global cylindrical Equal-Area Scalable Earth (EASE) grid (Armstrong and Brodzik 1995).

Quality Assessment

The FT-ESDR product accuracy was assessed in relation to daily maximum (Tmx) and minimum (Tmn) air temperature measurements from the global weather station network (approximately 3700 individual stations). Mean annual FT spatial classification accuracies were 92.2 ±0.8 percent (standard deviation) and 85.0 ±0.7 percent (standard deviation) for respective SSM/I PM and AM orbital nodes over the global domain and initial 20-year (1988-2007) record. The FT classification accuracy shows strong seasonal and annual variability and is reduced during active FT transition periods when spatial heterogeneity in landscape FT processes is maximized in relation to the relatively coarse (approximately 25 km) satellite footprint. Additional data quality control (QC) metrics were developed and provide more spatially explicit accuracy information, including potential negative impacts of temporal gaps in sensor data time series, open water, terrain, and land cover heterogeneity effects. The resulting database provides a consistent and continuous, multi-year record (1988 onward) of daily (AM and PM) FT dynamics for the global biosphere (Kim et al. 2011).

Surface air temperature records from global model reanalysis and in situ weather station networks were used for FT algorithm calibration and verification of FT-ESDR accuracy. Global meteorological reanalysis data were used to define the threshold levels and the global FT-ESDR domain (Figure 2) as all vegetated land areas where seasonally frozen air temperatures are a major constraint to ecological processes (Kim et al. 2011).

Figure 2. The global FT-ESDR domain defined from a Cold Temperature Constraints Index (CCI, days yr-1) and GMAO model reanalysis based daily Tmn over a 7-year (2000-2006) period. The FT-ESDR domain includes all vegetated land areas where the CCI ≥ 5 days yr-1.

The QC metrics employed provide an indicator of FT product quality for each grid cell within the FT-ESDR domain (Figure 3). The dynamic QC information includes the number of days per year with SSM/I radiometric brightness temperature data gaps and flagged precipitation events (Ferraro et al. 1996). The static QC information includes the potential effects of fractional open water cover (MODIS 17-class IGBP Global Land Cover Product, Friedl et al. 2002), complex topography (GLOBE, 1999) and heterogeneous land cover conditions defined from the 1 km resolution global land cover classification and Digital Elevation Model (DEM), and the average number of days (first year) with global model reanalysis air temperatures within ± 3 Celcius degrees of 0.0 Celcius degrees (Kim et al. 2011).

Figure 3. A FT-ESDR quality assessment was developed to identify regions of relative high to low quality of FT classification results in relation to general climate and landscape features. The QC map ranges from low (estimated accuracy < 70 percent) to best (estimated accuracy > 90 percent) quality categories. Areas in white are outside the FT-ESDR domain.

Sensor or Instrument Description

The SSM/I instruments are part of the the Defense Meteorological Satellite Program (DMSP) F-8, F-11, and F-13 satellites. The SSM/I instrument is a seven-channel, four-frequency, orthogonally polarized, passive microwave radiometric system. The instrument measures combined atmosphere and surface radiances at 19.3 GHz, 22.2 GHz, 37.0 GHz and 85.5 GHz. Please see the SSM/I Instrument Description Web page for more details.

5. References and Related Publications

Armstrong, R. L., and M. J. Brodzik. 1995. An Earth-Gridded SSM/I Data Set for Cryospheric Studies and Global Change Monitoring. Advances in Space Research 16: 155-63.

Brodzik, M. J. and R. L. Armstrong. 2008. updated daily. Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures, 1988-2007. Boulder, Colorado USA: National Snow and Ice Data Center.

Ferraro, R. R., F. Weng, N. C. Grody, and A. Basist. 1996. An eight-year (1987-1994) time series of rainfall, clouds, water vapor, snow cover, and sea ice derived from SSM/I measurements. Bulletin of the American Meteorological Society, 77(5), 891-905.

Friedl, M. A., D. K. McIver, J. C. F. Hodges, X. Y. Zhang, D. Muchoney, A. H. Strahler, C. E. Woodcock, S. Gopal, A. Schneider, A. Cooper, A. Baccini, F. Gao, and C. Schaaf. 2002. Global land cover mapping from MODIS: algorithms and early results. Remote Sensing of Environment, 83, 287-302

GLOBE Task Team and others (Hasting, D. A., P. K. Dunbar, G. M. Elphingstone et al.). 1999. The global land one-kilometer base elevation (GLOBE) digital elevation model, version 1.0. National Oceanic and Atmospheric Administration, National Geophysical Data Center, 325 Broadway, Boulder, Colorado 80305-3328, U.S.A. Digital data base at http://www.ngdc.noaa.gov/mgg/toto/globe.html and CD-ROMs.

Kim, Y., J. S. Kimball, K. C. McDonald, and J. Glassy. 2011. Developing a Global Data Record of Daily Landscape Freeze/Thaw Status using Satellite Microwave Remote Sensing. IEEE Transactions on Geoscience and Remote Sensing.

McDonald, K.C, and J.S. Kimball, 2005. Hydrological application of remote sensing: Freeze/Thaw states using both active and passive microwave sensors. Encyclopedia of Hydrological Sciences. Part 5. Remote Sensing. M.G. Anderson and J.J. McDonnell (Eds.), John Wiley & Sons Ltd. DOI: 10.1002/0470848944.hsa059a.

Related Data Collections

• Seasonal frost depths, midwestern USA
  
• Global Annual Freezing and Thawing Indices
  
• Arctic EASE-Grid Freeze and Thaw Depths, 1901 - 2002
  
• Modeled Daily Thaw Depth and Frozen Ground Depth
  
• Arctic Soil Freeze/Thaw Status from SMMR and SSM/I, Version 2
  
• Circumpolar Active-Layer Permafrost System (CAPS)
• Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures

Related Web Sites

• Freeze/Thaw Earth System Data Record
  

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 3.

Table 3. Acronyms and Abbreviations

Acronym	Description
DEM	Digital Elevation Model
DMSP	Defense Meteorological Satellite Program
ESRI	Environmental Systems Research Institute
EASE-Grid	Equal-Area Scalable Earth Grid
ENVI	Environment for Visualizing Images
FT-ESDR	Freeze/Thaw - Earth System Data Record
FTP	File Transfer Protocol
GIF	Graphic Interchange Format
HDF5	Hierarchical Data Format - Version 5
IDL	Interactive Data Language
PNG	Portable Network Graphics
JPL	Jet Propulsion Laboratory
MEaSUREs	Making Earth System Data Records for Use in Research Environments
NASA	National Aeronautics and Space Administration
QA	Quality Assurance
QC	Quality Control
SSM/I	Special Sensor Microwave/Imager

Document Creation Date

October 2010

Document URL

http://nsidc.org/data/docs/measures/nsidc0477_freeze_thaw/