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

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

In the case of Metop-A, to minimise the risk of failure to the AHRPT-B unit, while still offering the user community a service, EUMETSAT 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 is activated for all orbits over the North Atlantic and European area, starting at around 60°N. The AHRPT is then switched off before the spacecraft reaches the Southern Atlantic Anomaly region at around 10°N.

AHRPT operations are made in ascending orbits, but with more stringent risk reduction measures than applied for the descending passes given the availability of data via the Fast Dump Extract System (FDES) to cover the North Hemisphere. The same operational restrictions still apply over the polar caps and South Atlantic Anomaly.

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

AHRPT Reception

World map showing Metop-A AHRPT Switch-on Zone

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.

Under nominal operations the Metop 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).

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

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, 60 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 NWP-SAF:

Local processing software details
Software name Description Software Supplier/More information
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. SAF on Numerical Weather Prediction
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. SAF on Numerical Weather Prediction

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

Illustration showing ground station

The CCSDS source packets transmitted via Metop 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 (PDF, 102 KB).
  • 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, under Reception Station Design Documentation.

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 this, 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 website. The formula for computing UTC based on OBT_ISP and the correlation parameters are described in the Metop Space-to-ground Interface Specification, section 5.2.2.1.