Monitoring weather and climate from space Compression of Data for Regional Dissemination

EUMETSAT provided VIIRS Regional Service Kangerlussuaq Svalbard Athens Lannion Moscow Maspalomas VIIRS onboard Suomi-NPP 16 M-Band Channels (750m) Geolocated and Calibrated (SDR) Network of Direct Broadcast reception stations 15 min timeliness via EUMETCast During the implementation of the service a need was indentified to develop a Compact VIIRS SDR Product Format (Level 1) to achieve a cost efficient distribution of the VIIRS data via EUMETCast, EUMETSAT’s satellite based data distribution system.

CVIIRS EUMETSAT provided Conversion Tool Main Use Case The main use case is expected to be that VIIRS data distributed via EUMETCast in the Compact SDR format is converted back to the original VIIRS SDR format, as defined by NOAA, for further processing and visualisation by the service users. Compact VIIRS SDR Original VIIRS SDR Visualisation Applications From EUMETCast CVIIRS EUMETSAT provided Conversion Tool

Alternative Use Case Tools are currently under development by third parties for visualising and utilising the data directly from the Compact VIIRS SDR format without first reconstructing the Original VIIRS SDR format. Compact VIIRS SDR Visualisation Applications From EUMETCast

Product Content Original VIIRS SDR HDF5 Compact VIIRS SDR HDF5 Radiances Brightness Temperatures Reflectances Geolocation and Angles for each Pixel Meta Data Compact VIIRS SDR HDF5 Radiances Coefficients for converting to Brightness Temperatures and Reflectances Geolocation and Angles on Tiepoint Grid Meta Data – Full original set maintained

Representation of Observations – Radiances Only

Geolocation and Angles – At Tie Points Only Original VIIRS SDR For each Pixel Compact VIIRS SDR At Tie Points

Results The size of the resulting Compact VIIRS SDR product is a third of the original VIIRS SDR product; Operationally, an additional size reduction of approximately a factor 2 is achieved through applying the common bzip2 compression on the Compact VIIRS SDR product, altogether making the real-time dissemination via EUMETCast affordable; The Accuracy of the reconstructed Original VIIRS SDR is: Better than 10m in Geolocation; Better and 0.01 degree in Angles; Within the instrument noise for the Radiances, Brightness Temperatures and Reflectances.

Tool and Documentation Bidirectional conversion tool CVIIRS made available by EUMETSAT: A Compact VIIRS SDR Product Format User Guide (EUM/TSS/DOC/13/70802) is available from EUMETSAT and serves as a product format specification and as guide for users and developers of tools for handling, visualising and processing the Compact VIIRS SDR. Compact VIIRS SDR Original VIIRS SDR CVIIRS

Generalisation of the Product Format It is believed that the product format - with additional effort - could be generalised to serve as a compact format for all advanced imagers of the current and planned polar orbiting satellites; The main focus would be the geolocation data, angular data, time representation and the representation and conversion of the observations. Meta data within the product is more programme specific (processing software version numbers, file names, etc). Suggested to be kept as is within a programme specific section of the format.

Conclusion In addition to savings in communication cost, a standardised compact format has the advantage of giving users a more homogeneous experience of the image data from the Regional Service, which typically provides data from several families of polar orbiting satellites. Action/Recommendation proposed: Based on the work done in the context of the EUMETSAT provided VIIRS Regional Service, it is recommended that work is initiated to define a standardised compact product format, generalised to cover the advanced imagers of the current and planned polar orbiting satellites.