Metop direct dissemination

Metop Direct Readout

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. Readout of all instrument data can be achieved via Advanced High Resolution Picture Transmission (AHRPT).

Service description

Metop-B and Metop-C provide a full, global Direct Readout service.

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 Northern Hemisphere. The same operational restrictions still apply over the polar caps and South Atlantic Anomaly.

TD 18 — Metop Direct Readout AHRPT Technical Description

HRPT LRPT Direct Broadcast Services Specification

Multi-Mission Administrative Message (MMAM)

Users wishing to know the daily switch-on and off times of AHRPT and other spacecraft status information should consult the Metop Multi-MIssion Administrative Message in the UNS (click on relevant tab). For help read the Multi-Mission Administrative Message user guide.

AHRPT reception

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

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.

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.

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:

Recommendation regarding use of time stamp

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.
• 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 onboard 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.