EDOS Initiatives to Decrease Latency of NRT Data for LANCE

The EOS Data and Operations System (EDOS) is the primary supplier of NRT (near real-time) data to the NASA NRT user community known as the Land, Atmosphere NRT Capability for EOS (LANCE). EDOS provides NRT data for various instruments on the EOS missions Terra, Aqua, Aura, as well as for the NOAA missions Suomi NPP and NOAA-20. In this paper, the authors describe an overview of the EDOS multi-mission system with emphasis on the NRT products distributed for LANCE elements. Remote EDOS high-rate data capture systems are deployed at NASA ground stations which provide data-driven capture of high-rate science for EOS missions. The remote EDOS components transfer the science data via closed and open high-rate WANs to the centralized EDOS Level-zero processing systems located at Goddard Space Flight Center. EDOS produces session-based data sets especially for LANCE NRT use from a single ground station contact; this data is sent to dual LANCE destinations as part of the standard redundancy requirement for LANCE elements. EDOS-provided Level 0 data is processed into higher-level products by the LANCE elements, where these higher-level products are then made available to the wider NRT user community.

EDOS has implemented various latency improvements with the ultimate goal to have EDOS processing of NRT data keep up with the spacecraft data downlink, and begin transfer the NRT data to the LANCE elements within minutes of the end of the contact session. EDOS uses both closed and open IP networks. The open networks typically have higher bandwidth than the closed network connections. Historically, EDOS has used TCP transport on all of its closed network connections. With the architecture expansion to use open networks, the limitations of TCP were quickly realized with long round trip delays, so a cost-effective delay-tolerant solution which overcame the TCP round-trip delay was chosen: the UDP-based Data Transfer (UDT) protocol.

EDOS has streamlined its systems and infrastructure to minimize latency for NRT data delivery for LANCE, with an average packet latency from instrument observation to delivery to each LANCE element of just over one hour.