Low Rate Picture Transmission
Encyclopedia
The Low Rate Picture Transmission (LRPT) is a digital transmission system, intended to deliver images and data from an orbital weather satellite
directly to end users via a VHF radio signal. It is used aboard polar-orbiting, near-Earth weather satellite programs such as MetOp
and NPOESS
.
The system is an update and replacement of the existing analog system called Automatic Picture Transmission
(APT), which has been used since the 1960s aboard NOAA's TIROS
polar-orbiting satellites. The APT system provided only two image channels, which were at a reduced accuracy and resolution (8-bit, 4 km/pixel, two lines/second). Compared to the APT system, LRPT images are four times more accurate and contain twelve times the resolution. Further, the additional data from other sensors increases the applications of the satellites and the users who receive the signal.
(AVHRR) imaging sensor is provided approximately 40 kbit/s to transmit its three image channels, and the High Resolution Infrared Radiation Sounder (HIRS) is provided approximately 2900 bit/s. The packetized application system provides the flexibility to transmit and receive new types of data in the future using the same hardware.
The datastream is processed using a Reed-Solomon error correction, then convolution
encoded, interleaved, and padded with unique synchronization words. The resulting binary stream is approximately 160 kbit/s.
It is transmitted as an 80 kiloBaud
quadrature phase-shift keyed (QPSK) signal on an RF carrier in the 137 MHz-band, with an equivalent isotropically radiated power
level that varies between 3.2 dBW (2 watt
s) and 8.0 dBW (6.3 watts).
To ensure the low-complexity ground stations that previously received the APT signal would be able to access the LRPT signal, a design study was included with the LRPT specification. Labeled Annex A, it shows the calculations which approximate the worst-case link budget
for fixed, omnidirectional antenna
reception will be 4.9 dB when the satellite is 13° above the horizon, and improve to 8.6 dB at 30° or higher elevations.
The imager data is gathered into image "strips" of 2048 pixels wide and 8 rows tall before being compressed. Each packet contains three of these image strips, one for each image channel. To reconstruct a 2048x2048 image requires 256 consecutive AVHRR image packets.
, NOAA's final TIROS
-series satellite, NOAA has indicated it will move to a new system, such as LRPT, on future vehicles.
Receive NOAA satellites hand scanner http://pandatron.cz/?232&prijem_noaa_satelitu_rucnim_skenerem
Weather satellite
The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...
directly to end users via a VHF radio signal. It is used aboard polar-orbiting, near-Earth weather satellite programs such as MetOp
MetOp
MetOp is a series of polar orbiting meteorological satellites operated by the European Organisation for the Exploitation of Meteorological Satellites. The satellites are all part af the EUMETSAT Polar System. It is intended to replace the soon to be retired TIROS network...
and NPOESS
NPOESS
The National Polar-orbiting Operational Environmental Satellite System was to be the United States' next-generation satellite system that would monitor the Earth's weather, atmosphere, oceans, land and near-space environment. NPOESS satellites were to host proven technologies and operational...
.
Purpose
LRPT provides three image channels at full sensor resolution (10-bit, 1 km/pixel, six lines/second) in addition to data from other sensors, such as atmospheric sounders and GPS positioning information.The system is an update and replacement of the existing analog system called Automatic Picture Transmission
Automatic Picture Transmission
The Automatic Picture Transmission system is an analog image transmission system developed for use on weather satellites. It was introduced in the 1960s and over four decades has provided image data to relatively low-cost user stations at locations in most countries of the world...
(APT), which has been used since the 1960s aboard NOAA's TIROS
TIROS
TIROS, or Television Infrared Observation Satellite, is a series of early weather satellites launched by NASA, beginning with TIROS-1 in 1960. TIROS was the first satellite that was capable of remote sensing of the Earth. This initial remote-sensing effort was significant because it enabled Earth...
polar-orbiting satellites. The APT system provided only two image channels, which were at a reduced accuracy and resolution (8-bit, 4 km/pixel, two lines/second). Compared to the APT system, LRPT images are four times more accurate and contain twelve times the resolution. Further, the additional data from other sensors increases the applications of the satellites and the users who receive the signal.
Design
LRPT uses a packetized datastream transmitted at an approximately 62 kilobits per second (kbit/s) rate. Each sensor using the LRPT is considered an application and provided a percentage of the transmission bandwidth in the form of a virtual channel. For example, the Advanced Very High Resolution RadiometerAdvanced Very High Resolution Radiometer
The Advanced Very High Resolution Radiometer is a space-borne sensor embarked on the National Oceanic and Atmospheric Administration family of polar orbiting platforms . AVHRR instruments measure the reflectance of the Earth in 5 relatively wide spectral bands...
(AVHRR) imaging sensor is provided approximately 40 kbit/s to transmit its three image channels, and the High Resolution Infrared Radiation Sounder (HIRS) is provided approximately 2900 bit/s. The packetized application system provides the flexibility to transmit and receive new types of data in the future using the same hardware.
The datastream is processed using a Reed-Solomon error correction, then convolution
Convolution
In mathematics and, in particular, functional analysis, convolution is a mathematical operation on two functions f and g, producing a third function that is typically viewed as a modified version of one of the original functions. Convolution is similar to cross-correlation...
encoded, interleaved, and padded with unique synchronization words. The resulting binary stream is approximately 160 kbit/s.
It is transmitted as an 80 kiloBaud
Baud
In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
quadrature phase-shift keyed (QPSK) signal on an RF carrier in the 137 MHz-band, with an equivalent isotropically radiated power
Equivalent isotropically radiated power
In radio communication systems, Equivalent isotropically radiated power or, alternatively, Effective isotropically radiated power is the amount of power that a theoretical isotropic antenna would emit to produce the peak power density observed in the direction of maximum antenna gain...
level that varies between 3.2 dBW (2 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s) and 8.0 dBW (6.3 watts).
To ensure the low-complexity ground stations that previously received the APT signal would be able to access the LRPT signal, a design study was included with the LRPT specification. Labeled Annex A, it shows the calculations which approximate the worst-case link budget
Link budget
A link budget is the accounting of all of the gains and losses from the transmitter, through the medium to the receiver in a telecommunication system. It accounts for the attenuation of...
for fixed, omnidirectional antenna
Omnidirectional antenna
In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...
reception will be 4.9 dB when the satellite is 13° above the horizon, and improve to 8.6 dB at 30° or higher elevations.
Image data
The AVHRR image data, in its raw form, consists of three images, each composed of six lines per second, at 2048 pixels per line, using 10-bits per pixel. This yields a raw datarate of 368,640 bit/s; approximately ten times greater than the allocated bandwidth. Therefore, the data is compressed using the JPEG extended DCT compression, adapted to a fixed compression ratio with continuous operation (no header or trailer), to fit the virtual channel size.The imager data is gathered into image "strips" of 2048 pixels wide and 8 rows tall before being compressed. Each packet contains three of these image strips, one for each image channel. To reconstruct a 2048x2048 image requires 256 consecutive AVHRR image packets.
Current status
Although it is currently being flown on MetOp-A, LRPT has been permanently deactivated on that vehicle after causing interference with the High Resolution Infrared Radiation Sounder (HIRS) sensor.- "The initial investigations regarding the interference on MetOp-A HIRS have been completed, and the conclusion is that no scenario exists where LRPT on MetOp-A can be turned on without causing heavy interference on HIRS. Due to the operational importance of HIRS and the lack of an established LRPT user community, it is clear that LRPT will not be turned on again operationally on MetOp-A." - Announcement to NOAA from EUMETSAT on 5 February 2007
Future
The previously mentioned MetOp program intends to launch satellites every five years and maintain service through 2020. With While APT will continue to be transmitted on existing satellites, and will be used on NOAA-N'NOAA-N'
NOAA-19, designated NOAA-N prior to launch, is the last of the United States National Oceanic and Atmospheric Administration's POES series of weather satellites...
, NOAA's final TIROS
TIROS
TIROS, or Television Infrared Observation Satellite, is a series of early weather satellites launched by NASA, beginning with TIROS-1 in 1960. TIROS was the first satellite that was capable of remote sensing of the Earth. This initial remote-sensing effort was significant because it enabled Earth...
-series satellite, NOAA has indicated it will move to a new system, such as LRPT, on future vehicles.
External links
LRPT Meteor M N1,receivers and software (LrptRx.exe ,LrptProcessor.exe and DeJPEGger.exe) http://web.aanet.com.au/~ospiropo/index.phpReceive NOAA satellites hand scanner http://pandatron.cz/?232&prijem_noaa_satelitu_rucnim_skenerem