Apt » History » Version 5
Version 4 (PASCHOS, Alexandros, 03/02/2016 11:43 PM) → Version 5/19 (PASCHOS, Alexandros, 03/10/2016 11:36 PM)
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h1. *2.2 Automatic Picture Transmission*
APT means Automatic Picture Transmission. It is a system, developed in the 1960s, made to transmit low-resolution analog image for weather satellites. A complete APT image takes around 12 minutes to be built up at a rate of 2 lines per second. The data is broadcasted by the satellite. The stream is obtained by the AVHRR/3 instrument. Two channels with a low resolution are emitting all the time using VHF signals at reduced rates (around 120 lines/minutes).
The two channels are composed of :
* Channel A: A visible frequency range channel providing APT imagery during the day.
* Channel B: An IR channel providing APT imagery at any time of the day and the night.
h2. *2.2.1 Technical characteristics of APT*
- frequencies : 137-138 MHz (audible frequencies)- Bandwith : 34 kHz
- mode : NFM (NarrowBand Frequency Modulation)
- Modulation : 2.4 kHz AM (Amplitude Modulation) subcarrier on FM carrier
- a circularly polarized antenna is needed (RHCP)
- data resolution : 4 km/pixel at a line rate of 120 lines/minute or 2 lines/second
- transmitted power : 5W (37 dBm)
NOAA 19 : 137.100 MHz
NOAA 18 : 137.9125 MHz
NOAA 15 : 137.620 MHz
In following years, digital signals produced by Low Rate Picture Transmission (LRPT) systems will replace APT.
h1. *2.2 Automatic Picture Transmission*
APT means Automatic Picture Transmission. It is a system, developed in the 1960s, made to transmit low-resolution analog image for weather satellites. A complete APT image takes around 12 minutes to be built up at a rate of 2 lines per second. The data is broadcasted by the satellite. The stream is obtained by the AVHRR/3 instrument. Two channels with a low resolution are emitting all the time using VHF signals at reduced rates (around 120 lines/minutes).
The two channels are composed of :
* Channel A: A visible frequency range channel providing APT imagery during the day.
* Channel B: An IR channel providing APT imagery at any time of the day and the night.
h2. *2.2.1 Technical characteristics of APT*
- frequencies : 137-138 MHz (audible frequencies)- Bandwith : 34 kHz
- mode : NFM (NarrowBand Frequency Modulation)
- Modulation : 2.4 kHz AM (Amplitude Modulation) subcarrier on FM carrier
- a circularly polarized antenna is needed (RHCP)
- data resolution : 4 km/pixel at a line rate of 120 lines/minute or 2 lines/second
- transmitted power : 5W (37 dBm)
NOAA 19 : 137.100 MHz
NOAA 18 : 137.9125 MHz
NOAA 15 : 137.620 MHz
In following years, digital signals produced by Low Rate Picture Transmission (LRPT) systems will replace APT.