Topic: IMS Product Adjustments

Date/Time Issued: November 23, 2021 2112Z

Product(s) or Data Impacted:  IMS ASCII, GRIB2, and GeoTIFF Products

Date/Time of Initial Impact: December 15, 2021 1700Z

Date/Time of Expected End: Permanent change

Length of Outage: No outage, permanent change going forward

Details/Specifics of Change:

Several inconsistencies in the products of the U.S. National Ice Center’s Interactive Multisensor Snow and Ice Mapping System (USNIC’s IMS) are to be addressed no earlier than December 15, 2021. Users of the current IMS products will not see any interruptions to data delivery, but the resultant product files will change to reflect the updates described below.  Users should carefully read the scheduled change descriptions, and ensure their ingest process is compatible. 

Affected Products and Scheduled Changes:

1. ASCII Header

As the NOAA component of the USNIC has transferred from NESDIS to the NWS, the ASCII header will be updated to reflect this change. The number of characters within the ASCII header will change, but the number of lines will remain the same.

2. ASCII, GRIB2, and GeoTIFF Internal Filename

Currently, the filename of the .gz file and the internal file it contains do not match within the distributed ASCII, GRIB2, and GeoTIFF products. The internal filename will be renamed to match the compressed filename (without the .gz), whereas the compressed filename will not change. Common Linux command-line tools ignore the internal filename by default, and would be unaffected by this change.

3. GRIB2 Header

The datetime in the header of the Northern Hemisphere GRIB2 products is inconsistent, one day behind the reality of IMS product’s 00 UTC valid time. The date for the 00 UTC GRIB2 products will be adjusted one day ahead, representing the correct datetime. 

Additionally, the originating center and sub-center will be changed from NESDIS to NWS/OPC. 

4. GRIB2 Projection Change #1

The included projection metadata in the header of Northern Hemisphere GRIB2 products lists projection information for an oblate spheroid rather than the actual IMS projection. This change will correct the projection metadata to match the true IMS projection. 

5. GRIB2 Projection Change #2

The initial pixel lat/lon is indicated to be the upper right corner of the lower left pixel for the 1km GRIB2 products. It will be changed to be the centroid of the lower left pixel, matching the 4km GRIB2 products. Additionally, very slight adjustments to the initial pixel lat/lon for the 4km GRIB2 products will be made to improve precision. 

Sample data may be accessed at the following location: https://satepsanone.nesdis.noaa.gov/pub/30day/nic_ims/sample_data/

Please note: This upgrade will not be performed during Critical Weather Day (CWD).

Also, the contents of this release are subject to change based on user readiness, customer feedback, and management approval.

User feedback and questions should be directed to Walt Clark, U.S. National Ice Center/NWS OPC walter.clark@noaa.gov

Contact Information for Further Information: ESPC Operations at ESPCOperations@noaa.gov at (301)817-3880.

Web Site(s) for applicable information: See http://www.ssd.noaa.gov/PS/SATS/messages.html for this and other satellite related messages.

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