EASE-Grid 2.0: Incremental but Significant Improvements for Earth-Gridded Data Sets

Abstract

Defined in the early 1990s for use with gridded satellite passive microwave data, the Equal-Area Scalable Earth Grid (EASE-Grid) was quickly adopted and used for distribution of a variety of satellite and in situ data sets. Conceptually easy to understand, EASE-Grid suffers from limitations that make it impossible to format in the widely popular GeoTIFF convention without reprojection. Importing EASE-Grid data into standard mapping software packages is nontrivial and error-prone. This article defines a standard for an improved EASE-Grid 2.0 definition, addressing how the changes rectify issues with the original grid definition. Data distributed using the EASE-Grid 2.0 standard will be easier for users to import into standard software packages and will minimize common reprojection errors that users had encountered with the original EASE-Grid definition.Keywords: EASE-Grid 2.0; EASE-Grid; WGS 84; equal-area projections; Earth-gridded EASE-Grid History and AttributesDefined in the early 1990s as part of the NOAA/NASA Polar Pathfinder Program for gridded, satellite-derived passive microwave brightness temperatures, the Equal-Area SSM/I Earth Grid (EASE-Grid) was simple to use and understand. The original definition [1,2] specified three ISPRS Int. J. Geo-Inf. 2012, 1 33 projections together with the Backus-Gilbert interpolation method used for the SSM/I (Special Sensor Microwave/Imager) Pathfinder data set [3]. The EASE-Grid projection and gridding scheme was quickly adopted and used with different interpolation methods by the SMMR, AVHRR and TOVS Polar Pathfinder projects, and has been used in the production of numerous other data sets since then. Over time, the authors realized that the projection and gridding scheme had become so widely used that the SSM/I in the original name was a misnomer, since there was nothing SSM/I-specific about the projection and grid definitions. By 2002, Brodzik and Knowles [4] decided to retain the acronym but changed the meaning to "Equal-Area Scalable Earth-Grid", to emphasize the versatility of applications it enjoyed. Today, the term EASE-Grid refers to the three original projections and associated gridding scheme, but does not include prescriptions for binning or interpolation methods.The EASE-Grid definition [4] specifies a set of three equal-area projections together with an infinite set of potential grid (spatial resolution and coverage) definitions. The EASE-Grid projections comprise polar aspect Lambert azimuthal equal-area projections (Figure 1) for Northern or Southern Hemisphere, and a cylindrical equal-area projection with standard parallels at ±30• (Figure 2) for applications in midand low-latitude regions. The first EASE-Grids, defined for SSM/I gridded brightness temperatures at 25-km resolution, spanned the full Northern and Southern Hemispheres in the azimuthal aspects and the global projection to a latitude of ±86.72• . This poleward extent was inside the data area near the pole for SSM/I, where no data were collected by the sensor due to orbital inclina...

About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

“…Freeboard was only derived for regions with an SIC above 55 %. Monthly mean freeboard was computed from January to December and was gridded onto a 100 km EASE-Grid 2.0 (Brodzik et al, 2012). The individual processors are described in Sects.…”

Sensitivity of CryoSat-2 Arctic sea-ice freeboard and thickness on radar-waveform interpretation

“…Including radar freeboard, snow depth, sea-ice thickness and all auxiliary data products, data for 1 month are averaged on the EASE-Grid 2.0 (Brodzik et al, 2012) with a resolution of 25 km. For averaging radar freeboard and thickness we use the weighted arithmetic mean, which is calculated from all processed data points within the boundaries of a grid cell.…”

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 1: Product description

“…These characteristics were defined according to the satellite observations, and to ensure consistency with the forthcoming SMAP mission. The EASE2.0 grid (Brodzik et al, 2012) was chosen, and the grid cell spatial resolution set to 36 km × 36 km. These characteristics are appropriate for the Aquarius observations at latitudes higher than 50 • .…”

“…Since the Aquarius' sensors are in a push-broom alignment, weekly gridded product provides the largest spatial coverage. The gridded products were produced on the Equal-Area Scalable Earth version 2.0 (EASE2.0) grid (Brodzik et al, 2012). Each grid cell is 36 km × 36 km.…”