1. Introduction

1.1. Overview

Polar2Grid is a set of command line tools for extracting data from earth-observing satellite instrument files, remapping it to uniform grids if needed, and writing that gridded data to a new file format. It provides an easy way to create high quality projected images. Polar2Grid was created by scientists and software developers at the SSEC. It is distributed as part of the CSPP LEO project for processing of data received via direct broadcast antennas. Although Polar2Grid was created to serve the direct broadcast community, it can be used on most archived data files.

The features provided by Polar2Grid are accessible via bash scripts and binary command line tools. This is meant to give scientists an easy way to use and access features that typically involve complicated programming interfaces. Linux terminal commands included in these instructions assume the bash shell is used.

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1.2. Software Design

Polar2Grid has a modular design operating on the idea of satellite “products” or “datasets”; data observed by a satellite instrument. These products can be any type of raster data, such as temperatures, reflectances, radiances, or any other value that may be recorded by or calculated from an instrument. There are 4 main steps or components involved when working with these products in Polar2Grid: reading, writing, compositing, and remapping. Polar2Grid makes it possible to access and configure these steps with a simple bash script called polar2grid.sh and other helper scripts. More information on accessing Polar2Grid’s features and running its scripts can be found in the Polar2Grid Basics section or the examples following each reader section. Note that although an example may be written for a specific reader the same operations can be applied to all readers unless mentioned otherwise.

For more low-level information on the design and responsibility of each component see the Software Design Overview Appendix.

In Polar2Grid a majority of the functionality is provided by the open source SatPy library created by the Pytroll group. More information on SatPy and the capabilities it provides to python users can be found in the SatPy documentation.

1.3. What’s New?

Polar2Grid Version 3.1 is now available. This is a minor update that includes support for more VIIRS Science Products.

Included in this release:

• Support for additional VIIRS EDRs, including

  • Aerosol Optical Depth (AOD)

  • Cloud Top Height and Cloud Top Temperature

  • Surface Reflectances, including True Color

  • Vegetation Indices (NDVI, EVI)

• Support added for FY-3E MERSI-LL instrument

• Re-organization of software directories

• Optimizations

• Bug fixes

For more details on what’s new in this version and past versions see the Polar2Grid Release Notes in the github repository.

1.4. System Requirements

System requirements for the Polar2Grid software are as follows:

• Intel or AMD CPU with 64-bit instruction support (2+ cores - 2.4GHz)

• 16 GB RAM (minimum)

• Rocky 8 or Rocky 9 64-bit Linux (or other compatible 64-bit Linux distribution)

• 5 GB disk space (minimum)

1. Improved Execution Times

We continue to work to improve the efficiencies of Polar2grid. The table below presents a comparison of the unix real time required to create VIIRS and MODIS imager GeoTIFF files for the given segments of data in the default WGS84 projection. In these examples, the default 4 computer threads were used in the Version 3.1 executions. Execution times decrease when fewer bands and smaller data segments are processed. The table compares the execution times using Polar2Grid Version 3.1 with with those of Version 2.3.

Table of Execution Times for Creating GeoTIFF Default Projection Images

Instrument Input	Polar2Grid V2.3 True and False Color	Polar2grid V3.1 True and False Color	Polar2Grid2 V2.3 All Bands plus True and False Color	Polar2Grid V3.1 All Bands plus True and False Color
VIIRS SDR 10 - 86 second granules	4m52s	1m35s	12m54s	4m23s
MODIS Level 1B 3 - 5 minute granules	4m11s	2m34s	9m08s	2m32s

1.5. License and Disclaimer

Original scripts and automation included as part of this package are distributed under the GNU GENERAL PUBLIC LICENSE agreement version 3. Software included as part of this software package are copyrighted and licensed by their respective organizations, and distributed consistent with their licensing terms.

The University of Wisconsin-Madison Space Science and Engineering Center (SSEC) makes no warranty of any kind with regard to the CSPP LEO software or any accompanying documentation, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. SSEC does not indemnify any infringement of copyright, patent, or trademark through the use or modification of this software.

There is no expressed or implied warranty made to anyone as to the suitability of this software for any purpose. All risk of use is assumed by the user. Users agree not to hold SSEC, the University of Wisconsin-Madison, or any of its employees or assigns liable for any consequences resulting from the use of the CSPP LEO software.