The EARS-AVHRR collects AVHRR instrument data from the Primary Morning Orbit and Primary Afternoon Orbit satellites via a network of AHRPT/HRPT stations and retransmits it via EUMETCast. The current satellites providing AVHRR data are Metop-A and NOAA 19.
The Advanced Very High Resolution Radiometer (AVHRR) is a multi-purpose imaging instrument used for the global monitoring of cloud cover, sea surface temperature, ice, snow and vegetation characteristics.
To ensure the efficient and timely delivery of data the received HRPT data is handled in small chunks, or segments. This means that a more continuous flow of information can be passed through the communications network, and EUMETCast dissemination system, without significantly delaying it. The use of segments allows the system to monitor the data provided from the various stations and select which data is to be disseminated on the basis of quality. Segments also reduce unnecessary duplication of data that may have been acquired for the regions where more that one station has visibility of a spacecraft.
The stations acquire data as station segments of three-minute duration, from the satellite as it passes over the station locations. These segments are sent to the EUMETSAT computers, located at the organisation's site, which create user segments of one-minute duration. For each segment a message is sent reporting the availability of the segment and its completeness and quality to the central ‘decision-maker’ computer at EUMETSAT. The decision-maker will wait a short time to receive messages about available segments at the various remote computers and identify if there are any duplicate segments for the same time slot (duplicates arise due to station coverage overlaps). Finally, a decision is made as to which station has the best segment and this decision is sent to the particular remote computer instructing it to send the segment to the EUMETCast uplink server and on to users. This means that overlaps between stations are removed and end users should get a continuous set of ‘best quality’ segments for the regional pass. The one-minute segments that are disseminated to users via EUMETCast can be concatenated together by users to construct a regional pass.
AHRPT/HRPT Station Details
The subset of HRPT stations responsible for the collection of the satellite data and the resulting geographical coverage are provided in the figure below.
EARS-AVHRR geographical coverage
Data Processing and Delivery
Unlike EARS-ATOVS the EARS-AVHRR data remains unprocessed when retransmitted. The format and delivery mechanism is as follows:
For the NOAA service, the product file naming convention of files distributed by EUMETCast is as follows:
INSTNAME is the instrument name: avhrr
INSTNAME is the instrument name: AVHR
The EUMETSAT Advanced Retransmission Service (TD14) (PDF, 1 MB) — a technical description.
NOAA KLM User's Guide with NOAA-NN' Supplement