EASE-Grid: A Versatile Set of Equal-Area Projections and Grids

Mary Jo Brodzik and Ken Knowles

National Snow and Ice Data Center
Cooperative Institute for Research in Environmental Sciences
University of Colorado
Campus Box 449
Boulder, CO, 80309-0449

Email: brodzik@zamboni.Colorado.EDU

Link to full paper

The National Snow and Ice Data Center's (NSIDC) Equal-Area Scalable Earth Grid (EASE-Grid) comprises three equal-area projections, combined with an infinite number of possible grid definitions. The EASE-Grid is based on a philosophy of digital mapping and gridding definitions developed at the University of Colorado at Boulder.

The original, 25 kilometer grids were defined for data products generated by the NOAA/NASA Level 3 Passive Microwave Pathfinder Projects, which include gridded Passive Microwave Brightness Temperatures and related geophysical products derived from the Brightness Temperatures. However, the grids have been adopted by a number of other projects, including the TIROS Operational Vertical Sounder (TOVS) and Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinders, the Arctic and Antarctic Research Institute, St. Petersburg, Russia (AARI) Sea Ice data, and NSIDC's EASE-Grid versions of the Global Land Cover Classification (GLCC) data and the International Permafrost Association Permafrost and Ground Ice Map.

The gridding philosophy used to implement a library of software routines is based on the assumption that a gridded data set is completely defined by two abstractions, the map projection and an overlaid lattice of grid points, often referred to as "cells." The software may be used to define 10 projections, and convert gridded data between them. However, this presentation will be restricted to an overview of the family of specific projections and grids that we have called the NSIDC EASE-Grid, or simply EASE-Grid. The discussion will include how to define a map projection and grid definition in general, and our reasons for choosing equal-area projections and a spherical Earth model for our target applications in particular. It will include some examples of applications and an intercomparison between EASE-Grid data sets.

The EASE-Grid is intended to be a versatile tool for users of global-scale gridded data, specifically remotely sensed data, although it is gaining popularity as a common gridding scheme for data from other sources as well. Data from diverse sources can be expressed as digital arrays of varying grid resolutions, which are defined in relation to one of three possible projections. Storage as a simple digital array facilitates portability and ability to be imported into a user's favorite analysis package. Users find that visualization and intercomparison operations are then greatly simplified, and that the tasks of analysis and intercomparison can be more readily accomplished.

References

Armstrong, R. L. and M. J. Brodzik. 1995. An Earth-Gridded SSM/I Data Set for Cryospheric Studies and Global Change Monitoring. Adv. Space Res. 16(10):155-163.

Armstrong, Richard, M. J. Brodzik, A. Varani, 1997. "The NSIDC EASE-Grid: Addressing the need for a common, flexible, mapping and gridding scheme." Earth System Monitor, Vol. 7, No. 4, 3 pp.

Knowles, Kenneth W. 1993. Points, pixels, grids, and cells -- a mapping and gridding primer. http://www-nsidc.colorado.edu/NASA/GUIDE/docs/reference_documents/ppgc.html