Direct Dissemination

Direct Dissemination is the delivery of data, products and services to a user reception station, transmitted directly from Meteosat and Metop satellites.

Metop Direct Readout Overview - Small

Metop Direct Dissemination

The Metop Direct Readout Service provides local user stations with real-time transmission of data, limited to the instantaneous sub-satellite observation.

The data source is the satellite as it passes over the user's field of view, as illustrated in Figure 1 (right). Readout of all instrument data can be achieved via Advanced High Resolution Picture Transmission (AHRPT).

The NOAA direct readout HRPT system provides data from all NOAA-K,L,M,N spacecraft instruments. For further information on this service contact NOAA.

Service Description

Due to an earlier failure of the Metop-A AHRPT side A, the Metop Direct Readout Service no longer supports full global coverage.

Investigations into the failure of the Metop-A AHRPT side A have concluded that the root cause was heavy ion radiation, causing the failure of a component of the AHRPT Solid State Power Amplifier (SSPA). The investigations additionally concluded that the redundant Metop-A AHRPT-B sub-system is likely to suffer a similar problem. A retrofit of the failed SSPA component on board the future Metop-B and Metop-C spacecraft is underway.

Partial AHRPT Coverage — To minimise the risk of failure to the AHRPT-B unit, while still offering the user community a service, EUMETSAT has implemented a 'partial' AHRPT service in those areas where the risk of damage from heavy ion radiation is reduced. For southbound passes, AHRPT side B will be activated for all orbits over the North Atlantic and European area, starting at around 60°N. The AHRPT will then be switched off before the spacecraft reaches the Southern Atlantic Anomaly region at around 10°N. Figure 2 indicates the zone of activation of the AHRPT.

World map showing Metop-A AHRPT Switch-on Zone

Users wishing to know the daily switch-on and off times of AHRPT should consult the Metop Admin Message.

The switch-on of the AHRPT service for the descending passes over Europe, the North Atlantic and east Indian Ocean regions, will allow regional ASCAT, ATOVS, AVHRR and IASI data to be available from the EARS station network.

In a separate development, EUMETSAT will implement a Fast Dump Extract service, comprising the most recent part of the X-band global dump from the ascending passes of the ASCAT, AMSU, MHS, HIRS, AVHRR, and IASI data streams, thereby providing highly timely regional data for these instruments. This data will be made available via the EUMETCast-Europe service.

AHRPT Reception — AHRPT data is disseminated in L-Band, with a data rate of 3.5 Mbps. Local data coverage is of a radius of up to 1500 km.

Users operating existing HRPT stations will have to modify their stations in order to receive the "Advanced" Metop data. The adaptations, whose feasibility and scope depend upon the design of the existing station, will mainly require a modification of the receiver and the processing software. For further information on station equipment consult a manufacturer.

Diagram of an AHRPT Station

Under nominal operations the Metop-A Direct Readout data are openly available to all users within the service footprint. For information on access during periods of Data Denial users should consult the Data Denial User Guide (PDF, 110 KB).

Key Dissemination System — The Metop Direct Readout Key Dissemination System (KDS) is designed to provide registered users, in possession of Metop Station Key Units (SKU), with access to their Public Keys. Valid Public Keys are necessary for the operation of the SKU during periods of Metop data encryption. Access the Key Dissemination System

For help with using the KDS, please see the User Guide for the EPS EEIS Key Dissemination System (PDF, 88 KB).

Local Processing Software and Tools

Data received by the Direct Readout station can be processed further. The following local processing software is available under licence from the SAF on Numerical Weather Prediction

  • AAPP — ATOVS and AVHRR Pre-processing Package (AAPP) performs the end-to-end processing of Sounding and Imager data from the AHRPT/HRPT direct readout data stream.
  • RTTOVS — Radiative Transfer for TOVS (RTTOVS) is a very fast radiative transfer model for nadir viewing passive infrared and microwave satellite radiometers, spectrometers and interferometers.

Recommendation regarding use of time stamp

 

Meteosat Direct Dissemination

Meteosat satellites that offer direct dissemination

Meteosat-10 0° — services available via Direct Dissemination

  • Low Rate Information Transmission (LRIT)
    • Low Rate SEVIRI image data
    • Selection of meteorological products
    • Data Collection Platform messages
    • Meteorological Data Dissemination
    • Other Geostationary Satellite Data

Direct dissemination scheme (PDF, 17.8 KB)

TD 08 — MSG LRIT Direct Dissemination Service (PDF, 2 MB)

Meteosat-7 57°E — IODC services available via Direct Dissemination

  • High Resolution Image (HRI) data
    (Note that ITOT WEFAX formats also appear on the schedule — these are for EUMETSAT internal use only)

Dissemination schedule (PDF, 20.1 KB)

For the reception of the full set of Meteosat services, including the High Rate SEVIRI image data, users require access to EUMETCAST.

Direct Dissemination Reception

To receive the second generation Meteosat LRIT services (from the Meteosat-9 satellite onwards), users require a Low Rate User Station (LRUS). To decrypt any encrypted data received from the satellite, it is necessary to install a Station Key Unit (SKU) in the LRUS. SKUs are available from EUMETSAT at a cost of EUR 400.

To receive the first generation Meteosat data delivered via Direct Dissemination users require a Primary Data User Station (PDUS). To decrypt any encrypted data received from the satellite, it is necessary to install a Meteosat Key Unit (MKU) in the PDUS. MKUs are available from EUMETSAT at a cost of EUR 700.

For information on purchasing Direct Dissemination reception station equipment, contact a manufacturer.

To access services available via Direct Dissemination, users must register on the Earth Observation Portal (EOP).

Time stamp

The CCSDS source packets transmitted via Metop-A AHRPT contain the following time-stamp information:

  • UTC time-stamp in the secondary header (aka TMUTC), please see Metop Space-to-Ground Interface Specification, section 5.2.1.2.2, under EPS Technical Notes
  • Satellite Binary Time, abbreviated SBT (aka On-Board Time, OBT_ISP) in the ancillary data field, please see DJD Appendix A7-3 OBT-to-UTC correlation.

The EPS mission control centre maintains the on-board TMUTC source by uploading OBT-to-UTC correlation coefficients at regular intervals. Typically, the resulting accuracy of the TMUTC time stamp is in the order of +/- 0.007 second relative to UTC. However, this typical performance is not guaranteed and reliance on this parameter is not recommended. In light of the above, it is recommended that users strictly use the OBT_ISP time stamp and perform the translation to UTC in their ground processing via the OBT-to-UTC correlation parameters. These parameters will be sent via the ADMIN message and published on the EUMETSAT web pages.