NOAA Satellite Information System

About LRIT

Introduction

The digital Low Rate Information Transmission (LRIT) is an international standard for data transmission that was developed by the Coordination Group for Meteorological Satellites (CGMS) in response to a recommendation on digital meteorological satellite broadcasts. NOAA designed its LRIT system based on the CGMS standard. The LRIT/HRIT Global Specification can be located at http://www.wmo.ch/pages/prog/sat/documents/CGMS-03_HRIT-LRIT_v2-6.pdf (260 K). The NOAA LRIT system provides digital data, via a broadcast service, through its GOES East and GOES West geostationary satellites including both the GOES I-M and N-P Series. On the GOES-R series of satellites, the broadcast will be merged with the Emergency Managers Weather Information Network (EMWIN) service with a combined data rate of 400 Kilobits per Second. NOAA uses its LRIT broadcast system to disseminate Geostationary Operational Environmental Satellite (GOES) data, GOES Data Collection System (DCS), the National Weather Service’s Emergency Managers Weather Information Network (EMWIN) and other meteorological products to users using the 1691 Megahertz GOES L band down-link frequency. The NOAA LRIT product lists are shown below in tables 1 and 2.

 

Product Name Format Source Schedule Reference
GOES East Imagery:
1. Visible
2. Infrared.
3. Water Vapor.
LRIT System GOES Schedule http://www.ospo.noaa.gov/Operations/GOES/schedules.html
GOES West Imagery:
1. Infrared.
LRIT System GOES Schedule http://www.ospo.noaa.gov/Operations/GOES/schedules.html
Tropical Storm Products Graphic NOAA/NWS Hurricane Center Hourly http://www.nhc.noaa.gov/tafb_latest/
EMWIN Text National Weather Service As Received http://www.weather.gov/emwin/index.htm
DCS Text NOAA/NESDIS/OSO As Received http://www.noaasis.noaa.gov/DCS/
Meteosat (MSG) Graphic NOAA/NESDIS/OSDPD Hourly http://www.osdpd.noaa.gov/ml/info/index.html
Administrative Text Message Text LRIT System Administrators Hourly or As Needed N/A

Table 1: NOAA GOES East LRIT Content Table (Updated 092109)


 

Product Name Format Source Schedule Reference
GOES West Imagery:
1. Visible
2. Infrared.
3. Water Vapor.
LRIT System GOES Schedule http://www.ospo.noaa.gov/Operations/GOES/schedules.html
GOES East Imagery: Infrared LRIT System GOES Schedule http://www.ospo.noaa.gov/Operations/GOES/schedules.html
Tropical Storm Products Graphic NOAA/NWS Hurricane Center Hourly http://www.nhc.noaa.gov/tafb_latest/
EMWIN Text National Weather Service As Received http://www.weather.gov/emwin/index.htm
DCS Text NOAA/NESDIS/OSO As Received http://www.noaasis.noaa.gov/DCS/
Meteosat (MSG) Graphic NOAA/NESDIS/OSDPD Hourly http://www.osdpd.noaa.gov/ml/info/index.html
MTSAT Graphic NOAA/NESDIS/OSDPD Hourly http://www.osdpd.noaa.gov/ml/info/index.html
Imagery: Infrared Japan Meteorological Agency and NOAA/NESDIS/OSDPD Hourly N/A
Administrative Text Message Text LRIT System Administrators Hourly or As Needed N/A

Table 2: NOAA GOES West LRIT Content Table (Updated 092109)

 


GOES Imagery Processing

LRIT GOES imagery products are derived from the imager instrument on board the GOES spacecrafts.  The raw data stream is transmitted to the Command and Data Acquisition (CDA) station at Wallops, Virginia, where the is data received, processed, earth located, and formatted in the GOES Variable (GVAR) format. The data (Level 1A data stream) is then retransmitted to the GOES spacecraft from which the raw data stream was generated. This part of GOES processing system which is common for all GOES data processing systems is not presented on the NOAA LRIT System High Level Function Flow Chart (Figure 1).  Figure 1 begins with the reception of GVAR data at the NSOF and ends with the uplink of LRIT files from the CDA Wallops Island uplink processor.

LRIT function domains 1 through 5 diagram

Figure 1 High Level Functional Flows for LRIT Domains 1 through 5.


 

LRIT Domain 1: AFEP Level 1A ingestor

The LRIT Domain 1 (Advanced Front End Processor - AFEP) receives the GOES Variable format (GVAR) data and clock data through an antennae system from the Command and Data Acquisition (CDA) Station at Wallops, Virginia.  The AFEP parses the data and delivers the relevant visible and infrared images to the main processor.  The LRIT Domain 1 processor within the AFEP creates the Level 1A meteorological imagery products in a McIDAS area file format for distribution.  The LRIT Domain 1 system architecture consists of a primary and back-up server.

The Domain 1 processor builds partial image files or segments from a fixed number of scan lines in each image.  This subdivision of the full image reduces the size of transmitted files, reduces latency, and provides a means for a Domain 6 ground receiver workstation user to build an image even if some data are corrupted during transmission.



LRIT Domain 2/3: LRIT products processor.

The LRIT product processor (Domain 2/3) creates the files that will be broadcast over the GOES East and West broadcasts.  The Domain 2 and 3 reside on a single server and are referred to as LRIT Domain 2/3.  There is also a redundant, back-up server.  Currently, products processed within the LRIT Domain 2/3 include GOES imagery segments received from Domain 1; GOES DCS files received over the internet from the Wallops CDA; environmental products pulled from NOAA locations including tropical storm information from NOAA web sites; and text administrative messages inserted by NOAA personnel into the Domain 2/3.  Header records, metadata and images data are converted into LRIT format and transmission priority is set LRIT products processor and sent to Domain 4 for further processing and delivery to the Domain 5 at the Wallops CDA.

The metadata describes the file size and structure, image structure and navigation, creation time, product classification, and various other attributes of the data, where applicable. Packaged into LRIT header records, the metadata, when combined with the raw data, forms the LRIT file.



LRIT Domain 4: LRIT Communication processor.

The LRIT Domain 4 Communication Processor is an Intel-based, high-reliability server running the Linux operating system.  The Communication Processor receives files from Domain 2/3 and generates a compressed LRIT data stream of virtual channel data units (VCDUs).  Also added to the stream is an EMWIN stream.  EMWIN information is a bit-stream that is then converted to a simple file encapsulation.  The LCP uses the RICE lossless compression to condense LRIT data.  Domain 4 consists of 4 Linux box computers; a primary GOES-East, primary GOES-West and a backup server for each primary.  The entire LRIT data stream is then sent by the Domain 4 to the LRIT Domain 5 at the Wallops CDA.  Figure 2, on page 5, presents high level functional flow for Domain 4 and 5.

High level functional flows for Domain 1 through 5 diagram

Figure 2 High level functional flows for Domain 1 through 5.



LRIT Domain 5: LRIT Uplink processor

The Domain 5 is a Commercial Off-The-Shelf AVTEC Programmable Telemetry Processor.  Domain 5 maintains a constant uplink rate (IOC=146.942 kbps, FOC=293.884 kbps) to supply the transmitter with LRIT data stream.  The Domain 5 servers provide the physical layer processing and adds Reed-Solomon coding, interleaving, randomization and convolutional coding of the serialized data stream.  LRIT Domain 5 also buffers the data stream and maintains a constant data rate through the use of added fill data bits.  Domain 5 also adds a clock signal to the transmit modulators.



LRIT Domain 6: LRIT User station.

The LRIT User station is depicted on Figure 3 on page 6.  NOAA has two LRIT user stations at the NOAA Satellite Operations Facility (NSOF), Suitland, Maryland and another set at the Wallops Virginia CDA.  These receive stations serve as monitoring and quality control tools for the NOAA LRIT system. Two small antennas (1.6 m) for reception of GOES-East and GOES-West LRIT broadcasting are installed on NSOF building roof with a redundant antenna for each broadcast.  The NSOF LRIT user stations are equipped with standard software for LRIT data stream processing. Special software for monitoring and control LRIT transmission quality was additionally installed on these stations. The Help Desk Operators monitor the LRIT system availability on a 24/7 basis.

The LRIT Domain 6 user terminal is implemented using the lowest risk approach, while maintaining the NOAA low cost goal.  A typical user station consists of four main components as illustrated in Figure 3 below. The1.8-meter antenna is a parabolic dish antenna with no auto tracking. The downlink signal is received at 1691 Megahertz (MHz). The signal may be filtered to reduce adjacent channel interference and/or amplified by a low-noise amplifier. Then, it is down-converted to the Radio receiver IF frequency. The IF amplifiers have an IF bandwidth capable of receiving a 293 kbps symbol stream. The IF signal is then demodulated in the Receiving processor demodulator and the base band output to the Receiving processor is a serial bit stream. Domain 6 Work station receives this data stream, groups file segments, extracts and concatenates them and finally displays or stores the outputs.


LRIT User Station System diagram
Figure 3 LRIT User Station System.

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Satellite Products and Services Division
Direct Services Branch
Phone: 301-817-4521/4523
Fax: 301-817-3904
Mailing Address:
NSOF (E/SPO53)
1315 East-West Hwy
Silver Spring, MD 20910-3282     USA